dictionary of

by Herbert c. hanson

Dictionary of

Ecology
by

HERBERT

C.

HANSON

This practical dictionary

ecology and related

in

range

management,

for the use

is

and investigators

of students, teachers,

fields

forestry,

such as
wildlife,

conservation, agronomy, and limnology.

It is also

designed for use by the general

public for the better understanding of

widely used ecological terms. The Dictionary includes not only strictly ecological terms

but also those that have been

adopted from related

fields.

The aim

is

not to define words with final fixity but

rather to give clear, concise statements

indicating present-day usage.

nitions will

tating the

The

be useful, not only in

defi-

facili-

comprehension of ecological

concepts, but also in furthering the

re-

finement of both concepts and definitions.

The author

is

Plant Ecologist, Ber-

thoud, Colo., formerly Research Professor,

Dept.

of

Biology,

The Catholic

University of America.

A JH

From the

collection of the

.f

PreTinger
v

JJibrary
t

San Francisco, California

2007

DICTIONARY OF ECOLOGY

DICTIONARY OF
ECOLOGY
by HERBERT
The

C HANSON

Catholic University of America

Washington, D. C.

PHILOSOPHICAL LIBRARY

Copyright, MCMLXII

by Philosophical Library,

Inc.

Printed in the United States of America

Library of Congress Catalog Card

Number

This edition published by Bonanza Books,

a division of

Crown

Publishers, Inc.,

by arrangement with Philosophical Library, Inc.

d e

g h

60-15954

To DON, PHYLLIS,

DOROTHY

ABBREVIATIONS

cf.

confer,

compare

this definition

with the definition of

words that follow.

quod vide, indicating that it is desirable to look up

the definition of the preceding word in order to under-

q. v.

stand more fully the definition being considered.

Synonym.
words indicate that they are defined in this book,
or that such words form the scientific name of a plant or

Syn.

Italicized

animal.

PREFACE

The aim of this dictionary is to fill the need for definitions of many new terms that have come into usage during
the past thirty years and also to include many of the old
It has not seemed
words
that
are
many
rarely if at all
used at present and which are in the older glossaries. Many
words from fields closely related to ecology such as forestry,

terms that are used in current literature.

desirable to include

range management, agronomy, soils, and genetics are included because of their wide usage in ecological literature.
The definitions are usually those that are in accord with
present general usage. It has not seemed wise to attempt to
pronounce judgment on the desirability of, or the need for,
certain terms since such decisions are

made by usage

as a

language grows. The inclusion of certain words in this dictionary does not necessarily imply that the author approves
or recommends their use.

Words

are tools of thought. Clarification of the

meaning

of terms, precision in their use, and uniformity in usage

among workers in ecology and related fields are essential

in the growth of a science. When a concept or process can

be expressed precisely in ordinary language it appears unnecessary, and indeed detrimental to the growth of a science,

new

worth while to make ecological

wide a field of readers as possible.
As concepts and techniques become clearer and more precise
new terms are often needed, and when a new word is
accepted hi one branch of science it should be accepted in
to coin a

term. It

is

literature intelligible to as

other branches.
Definitions are not immutable.

As knowledge increases
hoped that this volume

the meanings of terms change. It is

will aid in the development of an increasingly useful ecological terminology.

of references are given below, many of which will

be found useful in securing further amplification of the
list

meaning of words in

this dictionary.

DICTIONARY OF ECOLOGY

Aapamoor

mosaic of high moor and low moor, consisting of

mounds covered with dwarf shrubs

circular or elongated

and sphagnum and depressions occupied by mostly sedges

and sphagnum.

Abicoen

The

non-biotic elements of a habitat.

Abioseston
See Seston.

Abrasion Platform

The part of the continental shelf and terrace on which

a horizontal plain is formed by long continued wave action.
Absolute Extremes

The

highest (absolute maximum) and lowest (absolute

minimum) values of a meteorological element, especially temperature, that have ever been recorded at a station.

Absolute Humidity
See Humidity, absolute.

Absorption Loss

The

initial loss of

capillary action

Abstract

and

water from a canal or reservoir by

percolation.

Community

generalized category comprising a number of similar

units or stands of vegetation and including animal life.

Abundance
The

number of individuals of a species in an area,

or
population,
community. The index of relative abundance
a
useful
gives
approximation of numbers relative to time or
space, e.g., the number of rabbits seen in an hour in a certain
total

place, cf. Density.

Abyssal
for

Refers to the deepest region of the ocean and often used

the zone in lakes below the profundal (q. v.). See

Archibenthal.

Abyssal-benthic (Abyssobenthic)

The

lower part of the abyssal region, below about 3300

feet (1000 meters).

Acarophytium
The symbiotic

relationship of mites

and

plants.

Acaulescent
Refers to a plant with inconspicuous, or seemingly absent,
stem above the ground.

Accelerated Erosion
Washing away or blowing away

of soil material in excess

of normal erosion (q. v.), resulting from changes in the
vegetation cover or ground conditions.

Accidental

species that occurs with a

Community-type.

low degree of Fidelity in a

Acclimation

The

increased tolerance or physiological adjustment of an

organism to a change in

its

environment.

Accommodation
Modification of the focus of the eye.

Accrescent
Refers to plants which continue to grow after flowering.

Accumulator Plant

A
in

plant that absorbs certain elements which accumulate

to a much higher degree than in most plants,
Equisetum concentrates large amounts of silica, cf.

its tissues

e.g.,

Seleniferous.

Acheb

short-lived

by mustards and

type of vegetation, characterized chiefly

grasses, in the Italian Sahara.

Achene

is

one-seeded, dry, non-opening fruit in which the seed

not attached to the wall of the fruit, e.g., sunflower

"seed."

Aciculignosa
Coniferous vegetation with small, evergreen, needle-like
leaves.

Acid Bog
See Bog.

Acidophilous
Refers to organisms that grow well or exclusively on
medium that is acid in reaction.

soil

or in a

Acid Soil

A soil with an acid reaction, containing more hydrogen

than hydroxyl ions; for practical purposes with a pH below
6.6.

Acldotrophic
Refers to organisms that feed on food having an acid
reaction.

Acquired Character

A modification of structure or function appearing during

the lifetime of an individual, caused by environmental conditions, e.g., broad leaves of some plants growing in shade.

Acre-Foot

The

quantity of water that will cover one acre one

foot deep.

Acre-Inch

The quantity of water that will cover one acre one

inch deep.
Acrodomatia
Structures

on plants

that shelter mites.

Acropetal
Refers to the development of organs in plants, the oldest
at the base, the youngest at the tip.

cf.

Basipetal.

Acrophytia
Plant communities in alpine regions.

Actic
Refers to the part of the seashore between tide marks.
See Littoral.

Actinometer

An

instrument which measures radiant energy, especially

the property that produces chemical

effects.

Actinometry

The measurement

of

chemical

reactions

caused

by

radiation.

Actinomycetes

group of organisms possessing very

fine

hyphae or

with bacteria or fungi. Various kinds

cause decomposition, disease, or produce antibiotics such as
threads,

classified

streptomycin

(q.v.).

Action

The impingement

of environmental factors such as heat

or light upon organisms.

Actium

A plant-animal community on a rocky seashore.

Activated Sludge
Material composed chiefly of bacteria and
in one method of sewage disposal.

protozoa, used

Actophilous
Refers to organisms that grow well on rocky seashores.

Adaptability
Capability of an organism to make changes which
better to its environmental conditions.

fit it

Adaptable
Refers to the adaptability of an organism.

Adaptation
(1) The process

or processes by which an organism becomes apparently better suited to its environment or for
particular functions. (2) The structures or activities of an
organism, or of one or more of its parts, which tend to fit it
better for life in

Adaptedness
The sum of
is

suited to

its

its

environment.

(3)

The

adapted form.

genetic characters by which an organism

environment.

Adaption
See Adaptation.

Adaptive Radiation
The evolution of taxa

(q. v.) as

they become adapted to

new

habitats, applicable also to the

development of a new

community.

Adaptive Selection
The evolution of more
but ecologically similar

or

less

similar forms in separate

areas.

Additive

A
to

material added to a

improve

its

fertilizer, or to another substance,

chemical or physical condition.

Adiabatic
Refers to an occurrence in which heat

is

neither gained

nor dissipated.

Adjustment
Processes by which an organism becomes better fitted to its
environment; functional, never structural, cf. Adaptation.

Adobe

A
to

fine calcareous clay or

make

silt,

may be mixed with

bricks for construction purposes,

cf.

water

terron.

Adsorption

The

attachment of molecules or ions to surfaces or interfaces such as solid-liquid, solid-gas, and liquid-gas boundaries.

Advance Growth
Young

trees in

openings or under the canopy in forests

before cutting or regeneration operations are started, syn.

Advance reproduction,

cf.

Second growth.

Adventicous Species
Organisms which have invaded from a distance.

Adventitious

An organ growing out of its usual location, e.g., root

from a stem; a species which has invaded from another area
and has become more or less naturalized.

Adventive

A plant growing spontaneously,

not native, ephemeral or

not spreading appreciably.

Aelophilous
Refers to dissemination by wind.

Aeolian
Refers to the wind, or to soil materials which have been
the wind or are subject to such movement.

moved by

Aeration

The

processes

by which

air

and other gases in a medium

are renewed or exchanged.

Aerobe

An

organism capable of living only in the presence of

free oxygen.

Aerenchyma
Tissue with thin-walled
cially

common

cells

and

large air spaces, espe-

in aquatic plants.

Aerial Photograph

vertical or oblique

photograph taken from the

air.

Aerobic
Refers to life or a process occurring only in the presence
of free oxygen. See Aerobe.

Aerobiosis
Life in the presence of free oxygen in the

medium.

Aerophyte
See Epiphyte.

Aeroplankton
Microorganisms floating in the

air, cf.

Plankton.

Aerotaxis
Involuntary response of an organism to a gas, such as
7

the curving of a plant toward a higher concentration of

oxygen.

Aestidurilignosa

Woodland

characterized by

mixed evergreen-deciduous

hardwoods.

Aestilignosa
Forest or woodland in which the woody plants are leafless
in winter and buds are protected by scales, e.g., beech forest.

Aestival
See Estival.

Affinity

The
common

relationship between

organisms that indicates a

used
origin;
occasionally to denote similarity of
communities.

Afforestation

The
where

process of establishing a forest

forest

on an

was not present previously,

Aftermath
The regrowth

of plants after

cf.

area, especially

reforestation.

mowing.

After-ripening
The dormancy period, following formation of the seed
that is required for changes in the embryo to occur prior
to germination.

Agameon
See Agamospecies.

Agamic
Asexual.

Agamogenesis
Asexual reproduction, parthenogenesis

Agamospecies
An aggregation

(q. v.).

of individuals in which reproduction oc-

curs almost exclusively

by asexual means,

syn.

Agameoo,

binom.

Agamospermy
Production of seed asexually, exclusive of vegetative
reproduction,

cf.

apomixis.

Age and Area

Willis* hypothesis that the older a species
the area that it occupies.

Age

the larger

is

Class
stand in which all of the trees originated in the same

regeneration period,

Age

is,

cf.

Even-aged.

Distribution

The

classification of individuals of a

population accord-

ing to age classes or periods such as prereproductive, reproductive,

and postreproductive.

Agglutination
Formation of clumps of microorganisms or

cell inclusions.

Aggradation
Building up of a portion of the earth's surface toward
uniformity of grade by deposition, as on the bottom of a lake.

Aggregate

A cluster of particles as a crumb of soil; to collect particles

into a cluster.

Aggregation
The coming

together of organisms into a group, e.g.,

clustered
about the parents. The condition of
offspring
into
a cluster or group, cf. Community.
collected
being

Agonistic Behaviour

An

activity such as fighting, feigning,

nected with conflict between animals.

and

escaping, con-

Agrarian Zone

The

portion of a country that can be cultivated.

Agrestal
Refers to an organism that grows in arable ground.

Agrology
The study

of

soils.

See Edaphology.

Agronomy
The

study of the production, processing, and use of farm

crops.

Agrophilous
Refers to organisms that grow well in grain fields or other

from man's

areas resulting

Agrostology
The branch

Horizon

The

activities.

of systematic botany dealing with grasses.

(Soil)

stratum of

soil consisting of

one or more of the

following layers. (A horizon, partly decomposed or matted

00 horizon,
plant remains lying on top of the mineral soil.
the relatively fresh leaves and other plant debris, generally

of the past year, lying on the

horizon.) AI horizon, the
surface mineral layer, relatively high in organic matter,
in
2 horizon, below the
x horizon,
usually dark in color.
the
than
in
color
places the surface layer, usually lighter

underlying horizon, in which leaching of solutes and

pended

materials occurs.

horizon,

more

like

sus-

horizon, transitional to the

than B, sometimes absent.

Aiphyllus
Evergreen.

Air layering
A method for producing

roots

position.

10

on a stem

in

an

aerial

Air-sacs
Thin-walled
some insects.

structures, containing air, in birds

and

in

Alar, Alary, Alate

Winged.

Albinism
Complete or almost complete absence of pigment, resulting in plants that are white in whole or in part, and in
animals with milky-white skin, light hair, and red pupils
in eyes.

Albino

An

organism deficient in pigment.

Alice's Principle

The extent of aggregation and the degree of density

of a population most favorable for optimum growth and
survival varies according to the species and environmental
conditions. Either deficiency or excess

may be

detrimental.

Aletophyte

weed growing

Algae
The
water or

in a mesic (q.

v.) habitat.

simplest kind of green plants, usually growing in

damp places, consisting of several phyla, formerly

classified in the

Thallophytes

(q. v.).

Algoid
Resembling an

Algology
The study

alga.

of Algae.

Alien

An

introduced plant which has become naturalized.

11

Aliquote

The

constant of temperature for a certain stage in the

life-cycle of an organism. See Temperature summation.

Alkali Reserve

The

total

amount

of dissolved salts or other substances

which tend to maintain the normal

alkalinity of a natural

water or the internal body fluid of an organism.

Alkali Soil

A soil

that has such a high degree of Alkalinity (pH 8.5

or higher), or such a high percentage of exchangeable sodium
(15 per cent or more), or both, that the growth of most crop
plants is reduced or prevented. See Black alkali, Saline soil.

Alkaline Soil

non-acid

soil

which contains more hydroxyl ions than

7.0 or higher; for

hydrogen ions; precisely, a soil with
with
or
7.3
practical purposes,
higher.

pH

pH

Alkalinity

The

chemical state of water or other substance in which

the hydroxyl ions exceed the hydrogen ions, usually with

pH 7.0 or higher, cf. Salinity.

Alleghanian Life Zone

One of the divisions of Merriam's Austral

life

zone

(q. v.),

east of the 100th meridian. See Life zone.

Allelarkean Society

An

independent,

Autarkean

dense,

fixed,

civilized

society,

cf.

society.

Allele

One

of the two forms of a gene located at a certain

position (locus)
allele of a pair
the character,
(q. v.)

on a homologous chromosome (q. v.). If one

is dominant to the other it
largely controls
is
dominant
over albinism
e.g., greenness

in seedlings.

12

Allelomimetic Behaviour
Two or more animals, mutually
ilarly.

stimulated, acting sim-

See Mimetic.

Allelomorph
See Allele.

Allelopathy
Influence of plants, exclusive of microorganisms, upon
each other, caused by products of metabolism.

Allen's Principle (Rule)

Appendages of animals tend to be shorter in cold regions,
resulting in reduced loss of heat. Cf. Bergmann's, principle.

Allergen

A substance which induces allergy, or causes symptoms to

show,

e.g.,

Pollen.

Allergy
Sensitivity resulting in pathologic condition in certain
people to substances such as pollen, food, hairs; or may be

caused by mental or environmental conditions.

Alliance

group of plant associations according to BraunBlanquet classified together on the basis of similarity in
floristic and sociological characteristics. See Association.
Allochoric
Refers to a species occurring in two or

more

similar

communities in the same region.

Allochthonous
Refers to deposits of material that originated elsewhere,
e.g., drifted plant materials on the bottom of a lake. cf.

Autochthonous.

Allogamy
Cross-fertilization (q. v.). See

13

Outbreeding.

Aliogenic Succession

The kind

of succession (q.

v.)

in which one kind of

community replaces another because of a change in the

environment which was not produced by the plants themselves, e.g., decrease in soil
cf.

Autogenic

moisture by improved drainage,

succession.

Allometry
Relationships in the evolutionary development of organs
or other characters of organisms which may bring about

disharmony, e.g., disproportionate development of antlers

and neck muscles of deer or moose.

Allopatric
Refers to organisms originating in or occupying different

geographic areas,

cf.

Sympatric.

Allopolyploid

polyploid (q. v.) which originated by the addition of

unlike sets of chromosomes, cf. Autopolyploid, Amphiploid.

Allopelagic
Refers to organisms occurring at any depth in the sea.

Allotrophic
Refers to lakes or ponds that receive organic material
by drainage from the adjacent land. cf. Autotrophic.

Alluvial Fan

fan-shaped deposit of sand, gravel, and fine material

from a stream where

its

gradient lessens abruptly.

Alluvial Soil
Soil that has

developed from transported and relatively

deposited material (alluvium), characterized by

or no modification of the original material by soil-

recently
little

forming processes.
14

Alluvium
Sediments, usually fine materials, deposited on land by
a stream.

Aim

A high mountain meadow,

alpine or subalpine.

Aim's Fb Coefficient

The

live
relationship of fish caught per hectare to the
hectare.
fauna
bottom
of
the
per
weight

Alpage

mountain or upland pasture of natural plants grazed

at the height of summer. See Aim.
animals
by

Alpha

Particle, * Particle

helium nucleus, given

off

by nuclei of certain

radio-

active substances.

Alpha Radiation

kind of ionizing radiation

particles are given off.

(q.

v.)

in which alpha

Alpha Ray

stream of alpha particles

(q. v.) cf.

Beta

ray.

Alpine
Refers to parts of mountains above tree growth or to

organisms living there.

Alternating Communities
See

Twin communities.

Alternation of Generations

The

life cycle of an
a
sexual
organism, especially
(gamete-producing) form with
a non-sexual (spore-producing) form; occurs in most plants

alternation of different forms in the

and in many animals.

15

Alternes

Two

or more communities alternating with each other

in a more or less restricted area.

Altherbosa
Communities with

tall

herbs, especially in

denuded

forest

areas.

Altimeter

An

instrument for determining altitude,

e.g.,

aneroid

barometer.
Altricial
Refers to the condition of delay after birth or hatching in
the attainment of a completely independent mode of self

maintenance,

cf.

Precocial.

Alvar

vegetation type consisting of dwarf shrubs resembling

steppe, in Sweden.

Alveolate
Pitted, appearing like a

honeycomb.

Ama nthophi lous

Refers to organisms living in sandy areas.

Ambulatorial
Refers to adaptations for walking in contrast to running,
associated with forest animals, cf. Fossorial, Scansorial.

Amendment
Any
is

material such as lime or synthetic conditioners that

worked into the

soil to

make

it

more productive;

usually

restricted to materials other than fertilizers.

Amensalism
The state or

which one organism is innot influenced, cf. Commensalism.

interaction in

hibited while the other

is

16

Ament

pendulous, spike-like cluster of flowers as in the oaks,

willows,

and

birches, syn. Catkin.

Amentaceous
Refers to plants with aments or catkins.

Ametoecious
Refers to a parasite that

is

restricted to a single host.

Amino Acid

class of

(q. v.);

and

at

organic

compounds containing

nitrogen, large

which become linked together to form proteins

each one containing at least one amino group (-NH 2 )
least one carboxyl (-COOH) group.

numbers

of

Amitosis
Direct division of the nucleus of the cell without mitosis
(q. v.).

Animate

A
(q.

compound

of

ammonium

sulfate used as

an herbicide

v.).

Ammocolous
Refers to an organism that grows in sand.

Ammonification
The formation

of

ammonium compounds from

organic

materials containing nitrogen.

Ammophilous
See Ammocolous.

Amnicolous
Refers to organisms inhabiting sandy banks of rivers.

Amniote
of

An animal such as reptile, bird, or mammal the embryos

which develop within a fluid-filled sac.
17

MMMMMMI

A Protozoan

(q. v.) in

the genus

Amoeba.

Amoebocyte

cell possessing

movement

similar to that of

Amoeba.

Amoeboid
Refers to

movement

similar to that of

Amoeba.

Amorphous
Refers to structures in which differentiation

is

not ap-

parent, shapeless.

Amphibia

of vertebrates (q. v.) comprising frogs, toads,

salamanders, newts, and related animals, most of which
spend part of the life-cycle in water.
class

Amphibious
Refers to organisms that can live in water or on land.

Amphicarpous
Refers to plants with two kinds of

Amphichromatism
The appearance on

fruit.

a plant of flowers with different colors

in different seasons.

Amphicryptophyte

marsh plant with amphibious vegetative

parts.

Amphidiploid
See Amphiploid.

Amphigean
An organism

that

is

native to both the old

worlds.

Amphigenesis
The union of gametes

to

form a Zygote
18

(q. v.).

and new

Amphlgenefic
Refers to an organism or a generation that produces
zygotes.

Amphimixis
Sexual reproduction in contrast to apomixis (q. v.). It
includes Allogamy (q. v.), Autogamy (q. v.), or a mixture of
these two.

Amphipodous
Refers to an animal having feet for walking and feet for

swimming.

Amphiphyte

plant growing in the border zone of wet land and

water, with amphibious characteristics.

Amphiploid (Amphidiploid)

kind of Polyploid (q. v.) in which there are two sets

of chromosomes, each set derived from a parent in different
species.

Amphirhinal
Refers to an organism with two noses.

Amphoteric
Refers to the capacity of a substance to react either as
a base or an acid.

Amplectcmt
Refers to clasping or twining for support,

e.g.,

tendril.

Amplexicaul
Refers to an organ clasping or growing around a stem
such as the base of a leaf.

Amplitude (Ecological)
The range of an environmental
19

condition or complex of

conditions in which an organism can exist or in which a

process occurs, cf. Tolerance.

Anabiont

perennial plant that produces flowers and fruits

many

times.

Anabiosis
Revival of an organism after apparent death, as for

example by

dessication.

Anabolism
The synthesis

of complex organic substances from simple

materials in organisms,

cf.

Catabolism, Metabolism.

Anadromous
Refers to animals having Anadromy.

Anadromy
The behaviour
live in the sea

of animals such as eels

and migrate into

Anaerobe
An organism

and salmon which

fresh water to breed.

living in the absence of free oxygen,

cf.

Aerobe.

Anaerobic
Refers to

life

or activity in the absence of free oxygen.

Anaerobiosis

The

existence of life under anaerobic conditions.

Anaerophytobionts
The anaerobic flora

of the

soil.

Analogous
Refers to an organ of one organism that corresponds in
function to an organ of another animal or plant but which
is not Homologous (q. v.), e.g. petioles of clematis and
leaflets of

peas as twining structures, wings of birds and

moths.

20

Anamniote

An
(q. v.),

animal lacking an embryonic membrane or amnion

Amniote.
e.g. frogs, fishes, cf.

Anandrous
Refers to flowers lacking stamens.

Anatomy
The branch

of biology that deals with the structure of

plants or animals.

Anchor-ice
Ice that has

formed on the bottom of a stream.

Andean
Refers to the Andes Mountains of South America.

Androconia
Modified

scales

on wings of Lepidopterons

(q. v.),

produc-

ing a sexually attractive odor.

Androdioecious
Refers to the presence of flowers with only stamens and
flowers with both stamens
cf.

and

pistils

on separate

plants,

Andromonoecious.

Androecium
The stamens

of a flower, collectively.

Androgen

substance causing the formation or maintenance of

characteristics in certain animals.

male sexual

Androgynous
Refers to flower clusters in which the staminate flowers
are attached above the pistillate flowers, e.g. certain sedges.

Andromonoecious
Refers to the presence of flowers with only stamens and
and pistils on the same plant,

flowers with both stamens

cf.

Androdioecious.
21

Androphile

plant that grows in the vicinity of

man and

his

activities.

Anemochore

species of which the seeds, spores, or other parts capable

of reproducing offspring are dispersed by wind, e.g. dandelion, cf. Diaspore, Disseminule.

Anemogram

continuous record of wind velocity made by an

anemograph.

Anemograph

self-recording instrument for recording the velocity

of the wind.

Anemometer
An instrument

that measures the velocity of the wind.

Anemophilous
Refers to plants in which the pollen or other spores are
almost exclusively by wind, e.g., willows, cf.

scattered

Entomophilous.

Anemoplankton
Plankton

(q. v.) that

Anemotaxis
The reaction

to

are transported

by wind.

wind by the movement

Anemotropism
The reaction to wind by

the

of a free organism.

movement

of an attached

organism.

Aneroid Barometer

An

instrument that registers atmospheric pressure in

may be calculated.

such a way that altitude

Aneuploid
Refers to the presence of an irregular

22

number

of chromo-

somes, fewer or greater than the multiple of the Haploid

(q. v.)

number,

cf.

Euploid.

Angiosperm
The subdivision

of Spermatophytes (seed-plants) in which

seeds are produced within the ovary, includes Monocotyle-

dons and Dicotyledons.

Angle of Repose
The maximum slope on which

soil

or loose rock remains

stable, syn. Critical slope.

Anhydrous
Refers to a substance that does not contain water,

e.g.

anhydrous ammonia.

Animal Unit

measure of converting kinds of livestock to a

common

standard in relation to forage resources on the equivalent

cow (live weight of about 1000 pounds). One

of a mature

animal unit in western range country equals about one head

of cattle, one horse, one mule, five sheep, five swine, or five
goats.

Animal Unit Month

measure of forage or feed requirement to maintain

one animal unit for 30 days.

Animation, Suspended
Animals of simple organization such as some nematodes,
snails, and rotifers which can endure long periods of drying
in an inactive condition.

Anion

negatively charged ion,

e.g.,

chlorine,

cf.

Cation.

Anisophylly

The

presence of two kinds of leaves on one plant as in

Selaginella

and some junipers.

23

Annelid

An
as

animal belonging to the phylum Annelida such

earthworms, leeches, and marine worms; showing

segmentation.

Annual Heat Budget

See Heat budget.

Annual Plant

plant which completes its life-cycle and dies in one

or
less; a winter annual starts growth in late summer or
year
fall and completes its life-cycle the
following spring or early

summer, a summer annual begins growth in the spring or

early summer and completes its life-cycle before the following winter,

cf.

Biennial, Perennial.

Annual Production
The amount of substance formed

in a year

by an organ-

ism or a group of organisms.

Annual Ring
The layer of wood (Xylem) added

each year to stems and

indicate
which
the age of the plant.
woody plants,
than
one layer may be formed in one
Occasionally more

roots of

year. See

Growth

layer.

Annual Seasons
The chief climatic

periods of the year; Vernal/ Estival,

Autumnal. (Serotinal), and Hibernal

Annual Succession
The successive occurrence
or their

activities,

(q. v.).

of plants or animals in an area,

during the year, such as summer-flowering

plants replacing the spring-flowering ones; or the various

reproductive stages in animals.

Annual Turnover
The total quantity

of living organisms (Biomass) (q.

in
an area.
in
one
produced
year

24

v.)

Animation
The variation from

year to year in abundance or behaviour of organisms caused often by differences in environmental conditions, especially precipitation and temperature.

Annulus

ring-like structure characteristic of certain plant parts

such as the stalk of mushrooms or on the spore-case of ferns.

In certain animals, notably fishes, a ring, arrangement of
rings, or other markings formed once a year and used in the
determination of age and rate of growth.

Anoestrum
The period

in animals

when

sexual desire or breeding

is

absent.

Anoxia
The condition

of oxygen deficiency as in the tissues of

an organism.

Antagonism
The depressive

of one organism upon another

grasses upon the growth of alfalfa, or

effect

one such as certain

the excretion of antibiotic substances such as penicillin by

a mold.

Antarctogaea
The Australian

zoogeographical region, excluding

New

Zealand and Polynesia.

Antecedent Moisture

The

degree of wetness of the

soil at

the beginning of a

run-off period.

Anther
The

pollen-producing part of the stamen in a flower.

Antheridium
The organ

in

which sperms are produced, found in

25

several groups of plants such as the algae, fungi, mosses,

and

ferns.

Anthesis

The

period

when

a flower

is

fully

expanded or when

fer-

tilization occurs.

Anthocyanin
Water-soluble pigments, usually red, blue, or violet in
the cell-sap of leaves, stems, flowers, and fruits of plants.

Anthropic (Anthropeic)
Refers to the influence of
influences, e.g.

a fertilized

soil

man

in contrast to natural

under crop

rotation.

Anthropochore

species that

regularly disseminated by man,

is

weeds, crop plants,

cf.

e.g.

Anemochore.

Anthropogenous
Refers to influences caused by man,

e.g. cultivation.

Anthropomorphism
The mode of thought or expression which
characteristics of man to non-human objects.

attributes

Anthropophilous
as

Refers to plants which grow in proximity to

weeds in cultivated lands or on paths.

man

such

Antibiosis

The

interaction

Antibiotic (q.

between organisms produced by an

v.).

Antibiotic

substance produced by organisms, especially bacteria

and fungi, which passes into the surrounding medium and
is toxic to other organisms, e.g.,
penicillin from the mold
Penicillium notatum destroys many kinds of bacteria.

26

Antibody

when

The

substance such as Antitoxin produced in an animal

foreign material (Antigen) is introduced into the body.

antibody counteracts the

effect of the antigen.

Anticline

formed by strata from

a common line. cf.
toward
dipping upward

geological structure or arch

opposite sides
Syncline.

Anticryptic
Refers to coloration which facilitates aggressive action
of an animal.

Anticyclone

mass of air of high atmospheric pressure compared to

adjacent areas, in which the circulation of the air is clockwise in the northern hemisphere, anti-clockwise in the

southern hemisphere.

Antigen
Parasites, substances produced by them, enzymes, toxins,
or proteins which cause the formation of antibodies in the
body of an animal.

Antitoxin

An

Antibody

(q. v.) that

counteracts a Toxin (q.

v.), e.g.,

antitoxin serum used in treatment of diphtheria.

Apatetic

The

coloration of an animal that causes

it

to resemble

cf.

Periodicity.

physical features of the habitat.

Aperiodicity

The

irregular occurrence of

phenomena,

Apetalous
Refers to flowers that lack petals.

27

Aphh
A plant

louse,

an insect in the family Aphides, feeds by

sucking juices of plants, e.g., green-peach aphid (Myzus persicae) which transmits more than 50 different plant viruses.

Aphotic Zone

The

deeper portions of bodies of water to which daylight

does not penetrate with sufficient intensity to influence organisms, cf. Disphotic, Euphotic, Photic zones.

Aphototropism
The response of an organism by which
the source of light,

cf.

it

turns away from

Phototropic.

Aphyllous
Refers to plants lacking leaves.

Aphytal Zone
The part of a
sublittoral

and

lake floor that lacks plants, includes the

profundal zones.

Apocarpous
Refers to flowers in which the carpels

joined together,

e.g.

(q.

v.)

are not

buttercup flowers.

Apogamy
The

reproduction of an organism without Fertilization

Apomixis, Parthenocarpy.

(q. v.). cf.

Apogeotropism
The response of an
earth,

cf.

organism by turning away from the

Geotropism.

Apomict Population

population of organisms produced asexually.

Apomixis
Asexual reproduction of organisms in contrast to Amphimixis (q. v.). It includes Vegetative propagation (q. v.) and
28

reproduction resembling sexual reproduction but in which

the egg and sperm do not fuse. cf. Apogamy, Parthenogenesis.

Aposematic
Refers to organisms that possess coloration associated with
harmful or distasteful contents, and therefore such organism
may be avoided by predators.

Appetitive Behaviour

The

reaction of an animal by which it becomes located

its needs.

or in a suitable condition to satisfy

Apron

A layer of material

a surface from erosion,

such as concrete or timber to protect

e.g.,

pavement below a

spillway.

Apterous
Refers to organisms or organs lacking wings,

cf.

Alar.

Aqueduct

conduit for water,

e.g.,

canal,

pipe,

tunnel,

or a

combination.

Aquiculture

The
of

use of artificial

means

fish, oysters, crabs, etc.,

to increase the production

in fresh or salt waters.

Aquifer (Aquafer)

or geological formation lying between

impermeable strata in which water may move for long
distances, yields ground water to springs and wells.

porous

soil

Aquiherbosa
Communities of herbs occurring in ponds and swamps.

Aquiprata
Communities of plants where ground water
e.g., wet meadows.

tant factor,

29

is

an impor-

Arable (land)
Land suitable

for cultivation

by plowing or

tillage,

does

not require clearing or other modification.

Arachnid

An animal

in the class Arachnida

mites, ticks, scorpions,

and

which includes

spiders,

king-crabs.

Arachnoid
Refers to an Arachnid, particularly spiders or spiderwebs; cobwebby.

Archaeophyte

weed introduced

in prehistoric time into cultivated

ground.

Archegonium
The organ producing

the egg in many groups of plants

such as mosses, ferns, and most Gymnosperms.

Archibenthal
Refers to the Archibenthic zone.

Archibenthic

The

Zone

layers of the

and 3300

feet,

ocean between depths of about 200 feet

the upper part of the Abyssal zone (q.

v.).

Arctic
Refers to the regions in high latitudes from which tree
growth is usually absent because of the shortness of the growing season and other unfavorable environmental conditions;

may

also

be used

as

noun

for the region.

Arctic-alpine
Refers to the arctic and alpine regions jointly.

Arctic Life Zone

One of Merriam's life zones (q. v.), the portion of the
Boreal life zone (q. v.) north of the limits of tree growth,
SO

southern limit marked by a normal mean temperature of

50 F. during the six hottest weeks of summer.

Arctogea
The faunal realm which
Palearctic,

Area
The
munity

includes the Ethiopian, Oriental,

and Nearctic regions

(q. v.). syn.

total territory or range in which a

occurs, cf. Basal area, Coverage.

Megagea.

Taxon or Com-

Areg

A sand desert.

Arenaceous
Refers to a sandy substratum.

Arenicolous
Refers to organisms inhabiting sandy substrata.

Areography
The study that

deals particularly with area.

Areole

small area of a leaf surrounded by intersecting veins.

Argillaceous
Refers to clayey material.

Arid
Refers to regions or climates which lack sufficient moisture for crop production without irrigation; precipitation
10 inches or less in cool regions, up to 15 or 20 inches in
tropical regions,

cf.

Semiarid.

Aridity

The

condition of dryness. See Arid.

Arid Transition Life Zone

The

western part of Merriam's Transition zone, lying

west of the 20-inch annual precipitation line.
31

Aril

on a seed, arising from base of the

sometimes pulpy or brightly colored as

special covering

ovule or the

stalk,

in the bittersweet.

Arrhythmic
Refers to the activity of an organism which occurs during
cf. Diurnal, Nocturnal.

both day and night,

Arroyo

stream channel or gully in an arid country, usually

with steep banks, dry

much

of the time.

Arthropod

An

animal in the phylum Arthropoda such as

insects,

crabs, spiders, centipedes.

Artifact

A substance

or appearance of a specimen of an organism or preparation of part of an organism which is not

(1)

present in the living tissue. (2) Something

especially

made by man

primitive man.

Artificial Selection
Selection by man of plants or animals which possess
desired qualities for reproduction and for the improvement
of the properties of the organisms,

cf.

Natural selection.

Artificial Stocking
The introduction of animals from another region, or the
artificial propagation of animals, into an area, e.g., stocking

streams with

fish

or introducing quail into an area where

they are scarce or lacking.

Asexual Reproduction
cf.

Reproduction of organisms without the fusion of gametes,

Apomixis.
32

Aspect
(1) One

of the seasonal appearances of vegetation. See

Aspection. (2) The direction toward which a slope faces.

Aspection

The variability in the appearance of vegetation or of its

constituent parts such as blooming, fruiting, foliation, and
defoliation during the various seasons of the year. Chief
seasons are Prevernal* Vernal, Estival, Serotinal, and Hibernal
(q. v.).

Assimilation

The
stances

synthesis of protoplasm

and other complex

sub-

by organisms.

Association

term with a number of usages, some of which are

defined. (1) An actual or Concrete community, Stand, or
group of organisms characterized by a definite floristic com-

physiognomy and strucand growing under uniform habitat conditions. (2) In

an abstract sense, a group of concrete communities or stands
that are classified together because they meet certain standards of similarity. See Association type, Index of similarity.

position, presenting uniformity in

ture,

(3)

In the Clements' sense, a Climatic climax

(q. v.)

unit

that includes all of the successional stages preceding or

associated with it. Plant association and animal association

emphasize populations of plants or animals respectively

within an area.

Association, Coefficient of
A measure of the frequency of occurrence together of
two species not due to chance, calculated by dividing the
number of samples in which both occur together by the
number of samples in which it is expected they would occur
by chance alone.
33

Association Complex
A group of associations which occupies a

definitely cir-

cumscribed area.

Association Fragment
A stand or group of plants that
teristics of its community type.

lacks

some of the charac-

Association, Index of
A measure of the occurrence together of one species with
another, calculated by dividing the number of samples in
which one species occurs by the number of samples in which
both occur.

Association, Interspecific

The occurrence together of two or more species, e.g.,

a parasite on a host, a grass and a legume mutually benefiting by growing in proximity to each other.
Association Segregate
A Climax community which has become differentiated
out of a mixed or undifferentiated vegetation under the influence of climatic change, e.g., the beech-maple association
arising as a segregate from the mixed deciduous forest in

southeastern United States.

Association Table

occurring in several stands of an

Community -type, and including data on such

listing of species

Association or

characteristics as
thesis table, cf.

abundance, cover,
Stand table.

vitality,

etc.

syn. Syn-

Association-type

A group of similar associations.

Associes
In the Clements' usage a temporary, developmental community, cf. Association (3).

34

Assortative Breeding (mating)

Pairing of male and female organisms

that involves

than chance so that mating of similar parents

is

more

favored.

Asymptotic Population
The maximum size reached by

a population under preenvironmental

matter how long reprono
conditions,
vailing
duction continues.

Atavism
The appearance

in an organism of

an

ancestral character

after a period of several generations.

Atlantic Period
See Sub-boreal period.

Atmometer
instrument for measuring evaporation such as a
porous porcelain sphere or open pan of water.

Any

Atoll

body of water, lagoon, surrounded by a coral

reef in

the ocean.

ATP
Adenosine triphosphate, an energy-rich phosphate compound in organisms, important in the transfer of energy.

Atrophy
Reduction in

size

or contents of an organ,

tissue,

or

cell.

Audiogenic Seizure
Convulsion in an animal caused by a high-pitched noise.

Aufnahme

(G)
See Sample area, Quadrat.

Aufwuchs

(G)
See Periphyton.

35

Aureomycin
The Antibiotic formed by

the

mold Streptomyces

aureofaciens.

Auroral
Refers to the

dawn or

the

morning Crepuscular period.

Austral Life-zone

One
montane

of Merriam's life-zones comprising most of nonUnited States and Mexico, bounded on the north

by a growing season of accumulation of 1 0,000 F. above 43 F.

and on the south by 26,000 F., with a mean daily temperature of 64.4 F. during the six hottest weeks at the northern
limit.

Australian Region
faunal region comprising Australia and New Guinea,
with Tasmania and smaller islands, in the realm Notogea

The

(q. v.).

Austroriparian Life-zone
A subdivision of the Lower Austral

life-zone, east of the

100th meridian.

Autarkean Society

simple, independent, economic human society consisting of nomadic or sparsely distributed individuals, cf. Allelar-

kean

society.

Autecology
The study

of the individual, or

members

of a species
considered collectively, in relation to environmental conditions, cf.

Ecology, Synecology.

Autochore

species in which the action of the parent plant is the

chief force of dissemination, e.g., the mechanical projection

of seeds in vetch,

cf.

Anemochore, Diaspore.
36

Autochthonous
Refers to local origin, e.g., an Indigenous species, deposits
produced within a lake. cf. Index speciesf Allochthonous.

Autoecious
Refers to parasites which pass

within or on the same host,

Heteroecious.

all stages

e.g.,

of their life-cycle

certain rust fungi,

cf.

Autogamy
(1) Self- or close-pollination leading to self-fertilization
in plants, cf. Geitonogamy, Xenogamy, Cleistogamous. (2)
Division of the nucleus into two parts followed by the union

of these parts in the same

cell,

occurs in some diatoms and

protozoa.

Autogenic Succession

successional series in

habitat in such a
e.g.,

way

that

which one
it is

stage modifies the

replaced by another stage,

deciduous forest replacing a pine

forest, cf.

Allogenic

succession, Succession.

Autolysis

The

dissolution or digestion of an organism or parts

thereof by

its

own

enzymes.

Autonomic
Refers to processes or activities arising from internal
causes, spontaneous, self-governing, e.g.

Mutation

(q. v.).

Autonomous
Refers to organisms, especially plants with chlorophyll,
that are Autotrophic (q.

v.).

Also used

as syn. of

Autonomic.

Autophyte

An

Autotrophic plant.

Autopolyploid

Polyploid

(q. v.) in

which three or more

37

sets

of like

(homologous) chromosomes have been derived from the same

species, cf. Amphiploid, Allopolyploid.

Autotomy
Loss of a part of the body of an organism by self-amputation followed usually by regeneration of the part, as in
certain arthropods and lizards.

Autotrophic
Refers to organisms which are capable of producing
organic substances from inorganic materials by means of
(1)

energy received from outside of the organisms, e.g., plants

with chlorophyll and certain bacteria, cf. Parasitic, SaprophytiCj Heterotrophic, Holophytic. (2) Refers to a pond or
lake that is restricted in its supply of organic material to that

produced within

its

own

confines.

Autumnal
Refers to the

fall

season or Aspect (q.

v.).

Auximone

non-essential organic substance such as an extract

secured from dung, of unknown chemical composition, which
stimulates the growth of certain plants such as duckweeds.

Auxin

A substance, natural or synthetic, that controls the growth

of plants,

cf.

Hormone.

Available Nutrient in Soil

The

part of the supply of nutrient materials such as

phosphates in the soil that can be absorbed by plants at rates

and amounts required

for growth.

Available Water

The

(in soil)
part of the water in the soil that plants can absorb.

Available Water-holding Capacity (of soil)

The amount of water available in the soil between
38

the

amount held at Field capacity (q. v.) and the amount

Permanent Wilting percentage (q. v.).

at the

Avalanche Cone
Materials such as rocks, snow,
base of the path of an avalanche.

ice, trees,

deposited at the

Avalanche Wind

wind, often destructive over a distance, produced by

an avalanche.

Average Distance
The distance between

plants determined by dividing the

square root of an area by the density of each species within
the area.

Avitaminosis

An

unhealthy condition or disease caused by a deficiency

of vitamins.

Awn
A bristle-like structure attached to plant parts such as on
Floret parts of grasses.

Azonal

A soil

(soil)

without a well-developed profile, occurring in any

of Parent material (q. v.), e.g.,

soil zone, consisting largely

recently deposited Alluvium,

dune

39

sand.

Back-crossing

The mating

its

or crossing of a hybrid with either one of

or
parents
parental stocks.

Back-fire

ahead of an advancing fire to

remove inflammable material and thus control the main fire.
started purposely

fire

Backftash
The movement
trees that

of a poison through root grafts from

have been treated with poison to non-treated trees.

Bacteriophage

virus

which destroys

bacteria.

Bacteriorhizae
The nodules on the

roots of most legumes and on some

other plants such as alders which contain bacteria that can
use atmospheric nitrogen in synthesizing organic compounds.

Badlands
Areas of rough, irregular, eroded land on which most of
the surface

is
occupied by ridges,
with sparse vegetation.

40

gullies,

and deep channels,

Baermann Funnel

A modification of the Berlese funnel (q. v.) for forcing

nematodes out of soil or debris. The funnel is filled with
warm water which forces the nematodes into a vessel below.
Baffle-pier

An

obstruction placed in the path of water moving at a

high velocity, e.g., a pier on the Apron of an over-flow dam.

Baffles

or similar devices placed in a conduit to check eddy currents below them, and provide a more
uniform distribution of velocities.
set of vanes, guides,

Limit

Bag

The maximum number

hunter may take legally.

of individuals of a species that a

Baguio

tropical cyclone
Philippine Islands.

or

Typhoon, a term used in the

Bajada
Outwash

slopes with long straight longitudinal profiles,

in
occur
southwestern United States.

Balance of Nature (Ecological Balance)

The state in an Ecosystem (q. v.) when the

interrelation-

ships of organisms to one another and to their environment

are harmonious or integrated to a considerable degree, e.g.,
a climax forest. This balance may be upset in many ways

such

change in environmental conditions (eroof many plants) or by a great increase

death
by
in numbers of a certain organism (grasshoppers in grassas

by a

drastic

sion followed

lands). See

Dynamic equilibrium.

Balanoid
Refers to barnacles.
41

Bald

treeless area in a forest vegetation, especially in the

southern Appalachians, occupied by grasses or shrubs usually.

Banados
Shallow swamps in Paraguay.

Bancroft's

Law

generalization that organisms and communities tend

to come into a state of Dynamic equilibrium (q. v.) with
their environment.

Band

A general term for a social group of two or more mobile

animals of the same species, e.g., a herd of deer, pack of
wolves.

Bank Storage
Water absorbed by the bed and banks of a stream and
returned in whole or in part after the Ground-water level
falls.

Bar

deposit of sand or rock particles forming a ridge

along the coast, usually at the mouth of a stream or across
unit of atmospheric pressure equivalent to 29.53
a bay. (2)
(1)

inches (750.1

mm)

of

mercury

at 32 F. in latitude

45.

Barachore

species in

which the

disseminated largely by
cf. Autochore, Diaspore.

seed, fruit, or other

its

own

weight,

e.g.,

Propagule is
walnut fruit,

Barchan

distinctive isolated sand

dune which

with the ends projecting leeward,

common

is

crescent-shaped
in Turkestan.

Bark

A general

term for

all

the tissues outside of the

in stems of trees; outer part

cambium

may be dead, inner part

42

is

living.

Barogram
The continuous

record

made by a

self-registering

Barometer.

Barograph

self-registering barometer.

Barometer

An

cf.

instrument for measuring the atmospheric pressure,

Aneroid barometer.

Barotaxis
Response by locomotion of an organism or part of an
organism in response to a barometric stimulus.

Barotropism
Reaction by growth curvature of a plant or a sedentary
animal in response to a barometric stimulus.

Barrens

An area in which vegetation is absent or poorly developed.

Barrier

topographic feature or a physical or biological condition that restricts or prevents migration of organisms or
prevents establishment of organisms that have migrated.
condition that prevents or appreciably reduces cross(2)
(1)

breeding of organisms.

Barrier Beach
See Beach.

Basal Area
(1)

The

area of the cross section of a tree at height of

4.5 feet above* the ground, usually expressed as the summation of the basal area of the trees in a forest in square feet

per acre.

(2)

The

surface of the soil actually covered or

a plant, especially the basal part, as compared

occupied by
to the full spread of the herbage; in grassland ecology often

43

measured
cover,

at

one inch above the ground

Ground

cover,

cf.

surface, syn. Basal

Cover.

Basal Cover
See Basal area

(2).

Basal Metabolism

The
it

is

rate of physiological processes in an organism when

carrying on a minimum of its life processes such as

respiration in order to remain alive.

Base Exchange Capacity

measure of the absorptive capacity of a soil for bases,

or exchangeable cations.
soil with a high base exchange

more plant nutrients and is less subject

one with a low exchange capacity.

capacity will retain

to leaching than

Base Flow
Stream flow originating from subterranean sources in
from surface run-off.

contrast to flow

Base Level
The lowest

level to

which a land surface can be reduced

by streams; the permanent base

Base Number
The Haploid

(q. v.)

level

number

is

the level of the sea.

of chromosomes (as found

in sperms or eggs, gametes) in those species with the lowest

number in a Polyploid series, or sometimes postulated for

a species that

is

extinct or

Base Saturation
The proportion

unknown.

of the Base exchange capacity that

is

saturated with metallic cations.

Basin Irrigation
A method of irrigation in which a level area is surrounded by an earth ridge so that a shallow body of water

may accumulate

prior to infiltration.

44

Basin- Listing
Alkind of land

which small dams

tillage in

at intervals

of 15 to 25 feet are formed across furrows to form basins

for collecting water after precipitation, thus retarding runoff
erosion.

and

Basipetdl
Refers to the development of organs in plants in which
the oldest are at the apex, the youngest at the base. cf.
Acropetal.

Basophilous
Refers to organisms which possess adaptations for

life

A triplex

spp.

in alkaline soil or in

an alkaline medium,

e.g.

Bathyal Zone

The deep

part of the ocean into which light does not

penetrate effectively.

Bathybic
Refers to

life

in the Bathyal zone.

Bdthypeldgic
Refers to deep portions of the ocean, not including the

bottom.

Bathysphere

structure consisting of a spherical

man

chamber

in

which

can descend deep into the ocean to make observations.

Bayou

marshy body of water caused by seepage, lack of

drainage, or floods, tributary to a stream or lake, in flat

term used in the Gulf Coast region and in the
country.

lower Mississippi River basin.

Beach
The

line or zone of demarcation

between land and water

of lakes, seas, etc. Barrier beach; a ridge of deposits separated

from the mainland by an interval of water.

45

Beach Pool
(1) Barrier

a shallow lagoon formed inland

Sand spit beach pool is a shallow

beach pool

from Barrier beaches.

is

(2)

lagoon generally sigmoid-shaped inland from a sand Spit,

characteristically on the protected side of a headland.

Beaufort Scale
A series of numbers devised by Francis Beaufort in 1805
to designate approximate wind velocities ranging from
for
a calm to 12 for a hurricane with wind velocity in excess of
75 miles per hour.

Beckmann Thermometer

thermometer graduated to 0.01 degree and covering a

scale of 6 to 7 degrees.

Bed Load
and other debris rolled along the bottom of
a stream by moving water, in contrast to "silt load" which
Soil, rocks,

carried in suspension.

is

Bedrock
The solid rock underlying soils

or other surface materials.

Behaviour, Appetitive

its

reaction of an animal that aids in the satisfaction of

needs.

Behaviour, Displacement

The

reaction of an animal that

not pertinent to the

stimulus, as when it cannot respond appropriately or when
two or more incompatible drives are present.
is

Behaviour, Instinctive

A fixed pattern of action

that

is

inherited.

Belt

A comparatively narrow
distinctive characteristics
cf

area or strip of vegetation with

from adjoining areas or vegetation.

Zone.

46

Belt Transect

strip of vegetation, usually a few inches or feet wide,

in which the constituent plants are recorded or mapped.

Bench Mark

point of reference used in elevation surveys.

Bench Terrace
A shelf-like embankment

of earth constructed along the

contour of sloping land to control run-off and erosion, cf.

Ridge

terrace.

Benthic
Refers to the bottom of any body of water. In the ocean
the benthic division is divided into the Littoral, Sublittoral,

Archibenthic, Abyssal-benthic zones,

(q. v.). cf. Pelagic.

Benthos
on or in the bottom of the ocean or
water, from the water's edge down to the

Organisms which
bodies of fresh
greatest depths,

cf.

live

Nekton.

Bergmann's Principle (Rule)

The generalization which states that Homoiothermal
(q. v.) animals such as birds and mammals in cold regions
and have a lower ratio of body
than
related animals in warmer
body weight

tend to be larger in
surface

to

climates.

The

size

reverse

relationship

is

shown by

thermous animals, especially amphibians and

Poikilo-

reptiles,

cf.

Allen's principle.

Berlese Funnel

An apparatus in which soil or debris is placed in a funnel,

heat and light applied from above as a rule, which forces
mites, collembolons, etc., into a vessel below, cf. Baermann
funnel, Tullgren funnel.

Beta Particles
High-speed electrons given

47

off

by radioactive substances.

Beta Ray

stream of Beta particles with greater power of penetration in the tissues of organisms than Alpha rays (q. v.).

B Horizon

A master soil

horizon between

and

Horizons

(q. v.),

a layer of Illuviation (q. v.) in which materials from overlying

horizons are deposited. B! is transitional between 3 and B 2 ,

but more

like

than A.

B2

is

the layer of

maximum

illuvia-

tion especially of silicate clay materials, or of iron and

organic materials, or with maximum development of blocky

or prismatic structure.
horizons, often absent.

Bicentric
Refers to a Taxon
or evolution.

B3

transitional

is

(q. v.)

between

B and C

with two centers of dispersion

Biennial

plant that lives for two years, usually blooming and

and then dying, e.g. carrot.

fruiting only in the second year

Biflorus

A plant that flowers in both spring and autumn.

Bilateral

An

Symmetry

organism which can be divided so that each half is

the mirror image of the other, e.g., vertebrates, snapdragon
flower, syn. zygomorphy. cf. symmetry.

Binary

Name

See Binomial.

Binom
See Agamospecies.

Binomial
A name
Quercus

of organisms

consisting

alba, the white oak; the first

second the species.

48

of

name

two words,
is

e.g.,

the genus, the

Bio-assay
The employment

of living organisms to test the effects

of a substance such as feeding rats with food containing

herbicide residues.

Biocenose
See Biocoenosis.

Biochemical

test for

Oxygen Demand

(B.O.D.)

and measurement of pollution in

oxygen that has been used by oxidiz-

the detection

which the quantity of

able materials under standardized conditions

is

determined.

Biochore

subdivision of the Biocycle (q. v.) It comprises a group

of Biotopes (q. v.) which resemble one another. The principal biochores are grassland, forest, savanna, and desert. The
desert biochore includes sandy desert
topes,

cf.

and stony

desert bio-

Biosphere.

Bioclimate
See Microclimate.

Bioclimatic

Law

(Hopkins)

The

generalization that in temperate North America

Phenological events generally occur at the average rate of
four days to each degree of latitude, 5 of longitude, and

400

feet of altitude; later

in spring

northward, eastward, or upward

and early summer, and

earlier in late

summer and

autumn.

Bioclimatology

The

study of the interrelations of organisms and climate.

Biocoenology
The study of communities

including qualitative and

the
quantitative analyses;
Synecology, Synchorology, Dynamics, and classification of communities.

49

Biocoenosis (Biocoenose)

The aggregate of interacting organisms living together

in a particular habitat, e.g., an oyster-bed community, usually
containing producer, consumer, reducer, and transformer
organisms,

cf.

Ecosystem, Community, Association.

Biocoenotics
See Biocoenology.

Biocycle

subdivision of the Biosphere (q. v.). Biocycles usually

recognized are saltwater, freshwater, and land; each consist-

ing of Biochores

(q. v.) cf.

Biotope.

Biodemography
The mathematical

treatment of population problems.

Bioecology

The branch

of biology that deals with the interrelations

of organisms among themselves and with their environments,
stressing the inclusion of both plants and animals, cf. Ecology.

Biogenesis

The

principle that living organisms can originate only

from other living organisms,

cf.

Spontaneous generation.

Biogenic
Refers to biological origin.

Biogeochemical Cycle

The

circulation of chemical elements such as nitrogen,

carbon, etc., in specific ways from the environment into

organic substances in animals and plants and back again into

the environment.

Biogeocenose

A concrete or actual Ecosystem

Biogeographic Region
See Biome.

50

(q. v.), e.g., a certain

bog.

Biogeography
The branch of

biology that deals with the geographic

and animals, cf. Plant geography,

distribution of plants

Zoogeography, Chorology.

Biointization
Preliminary treatment for seeds with chemicals to stimulate growth.

Biological Clock
The rhythmic occurrence of processes in organisms at
periodically timed intervals, e.g., the ejection of spores by
the fungus Pilobolus sphaerosporus.

Biological Control

The

use of organisms or viruses to control parasites,

weeds, or other pests, e.g. control of the cottony-cushion scale
by the lady beetle, prickly pear cactus in Australia by the
insect Cactoblastis cactorum.

Biological Efficiency

The ratio of the productivity of an organism, or a group

of organisms, to that of its supply of energy, cf. Productivity.
Biological Equilibrium
See Biotic balance.

Biological Factor

An

influence resulting from biological as distinct from

physical and chemical agents, including both Biotic factors
(q. v.)

and physiologic

factors such as

Hormones.

Biological Race (Strain)

A group of organisms which differ only in their physiological or ecological behaviour from other groups in the same
species.

Biological Spectrum
A tabulation by percentages of the plants of a community
51

or region into the life-form classes according to Raunkiaer's

classification (q. v.).

Biologies
Biological products such as vaccines, serums, etc.

Bioluminescence
Emission of light by living organisms such
jelly fish, etc.,

Biomass
The total

as fireflies,

popularly "phosphorescence."

quantity at a given time of living organisms of

one or more species per unit of space (species biomass), or of

all the species in a community (community biomass). cf.
Yield, Productivity , Standing crop.

Biome

A major biotic community composed of all the plants and

animals and communities, including the successional stages
of an area; the communities possess certain similarities in
physiognomy and in environmental conditions. Similar to

Formation

(q. v.), e.g.,

the North American grassland,

cf.

Biotic province, Biome-type.

Biome-type

A group of similar Biomes, e. g., the temperate deciduous

biome-type which includes the deciduous forests of eastern

North America, China and Manchuria, and Europe.

Biometry
The application

of the science of statistics to the study

of organisms.

Bionomics

The

study of organisms in relation to each other and to

the environment, cf. Ecology.

Biorealm
See Biome-type.

52

Bios
Plant and animal

life.

Bioseston

The

living

components of the Seston

(q. v.).

Biosocial Facilitation
See Facilitation, social.

Biosphere

The

portion of the earth and

its

atmosphere that

is

ca-

pable of supporting life; may be subdivided into Biocycles,

Biochores, Biotopes (q. v.).

Biosystem
See Ecosystem.

Biosystematics

The

study of living organisms for the purpose of recog-

nizing and differentiating biotic units and their

into taxa on the basis of genetic relationships.

classification

Biota
All of the species of plants and animals occurring within
a certain area or region.

Biothermal Zones

The divisions according to Merriam of the flora and

fauna of North America on the basis of temperature data.
Biotic
Refers to
Biotic

life, living.

Area

A general term to denote any large area that can be delimited

its

from adjacent areas on the

basis of the composition of

Biota.

Balance (Biological Equilibrium)

The state of more or less self-regulation of

Biotic

53

the-

numbers

of plants and animals in a community, brought about by

interactions within and between species and by the effects of

environmental conditions,
Pyramid of numbers.

cf.

Life-cycle,

Balance of nature,

Biotic Climax
See Climax.

Biotic District

According to Dice a subdivision of a Biotic Province, distinguished by ecologic differences of less importance than
those that separate biotic provinces.

Environment
The living parts of

Biotic

group

the environment of an organism or

of organisms.

Biotic Equilibrium
See Biotic balance, Balance of nature.
Biotic Factor

Environmental influences caused by plants or animals

such as shading by trees or trampling by animals, sometimes
used to include effects of non-living organic matter, cf. Biological factor, Coaction.

Biotic Formation
See Biome.
Biotic Influence
See Biotic factor.

Biotic Potential
The inherent capacity of an organism to reproduce and
survive,

which

environment,

is

cf.

pitted against limiting influences of the

Reproductive potential,

Environmental

resistance.

Biotic Pressure

The

activities of

an enlarging population
54

to

maintain

itself

and spread, or the tendency of one or more

extend

its

Biotic

Province

range,

cf.

species to

Population pressure.

major ecologic portion of a continent, occupying a

continuous geographic area, containing one or more regional
communities of plants and animals, e.g., Hudsonian biotic
province which occupies most of Canada and Alaska (Dice),
cf. Biome, Formation.
Biotic Succession
See Succession.

Biotin

growth-promoting or stimulatory substance (vitamin

H), a member of the vitamin B complex.

Biotope

The

smallest geographic unit of a habitat, characterized

by a high degree of uniformity in the environment and in its

plant and animal life, e.g., a decaying stump, a sandy beach,
cf.

Biochore.

Biotype

group of individuals occurring in nature, all with

essentially the same genetic constitution. A species usually
consists of

many

biotypes.

cf.

Ecotype.

Bipolar Distribution
Discontinuous distribution of a Taxon in the northern

and southern hemispheres.

Birge's Rule

is

generalization which states that the Thermocline (q.v.)

the transition stratum in lakes in which the temperature

decreases at the rate of at least

1C.

per meter of depth.

Bisect

line transect

which shows the

55

vertical

and

lateral dis-

tribution of roots along the side of a trench in the soil and

the above-ground parts of the plants along the line.

Bisexual

The

presence of functional male and female organs in

the same plant or animal, cf. Hermaphrodite, Dioecious,

Monoecious.

Bivalent

pair of

Homologous chromosomes

in a certain stage of

cell division.

Bivoltine
Refers to organisms with two generations a year.

cf.

Uni-

voltine, Multivoltine.

Black Alkali
Highly alkaline

soil

covered with a dark incrustation of

carbonates of sodium or potassium, cf

A Ikali soil, Saline soil.

Black Earth
See Chernozem.

Blizzard

A storm
drives fine

in which the cold wind, usually of high velocity,

snow and often ice crystals; the visibility is greatly

reduced.

Bloom
(1)

fine pale gray granular layer, often

waxy, occurring

commonly on
fruits, e. g.,

the surface of plant organs such as leaves and

the grape fruit. (2)
sudden appearance of brief

duration of large numbers of minute organisms, usually

algae, in bodies of water.

Blowout

An

excavation in loose

soil,

wind.

56

usually sand, produced by

Blytt-Sernander Scheme

The

chronological series of floras and kinds of vegetation

following the last glaciation in Scandinavia; comprising the
boreal, Atlantic, sub-boreal,

Bog
An

and sub-Atlantic

undrained or imperfectly drained

stages.

area,

with a vegeta-

complex composed of sedges, shrubs (Ericaceous, especially), and sphagnum mosses, typically with peat formation;
often with an area of open water. Frequently used in various
tion

meanings, in the sense of Marsh, Swamp, Moor, Fen.

Muskeg, Heath, Raised bog.

Bog

cf.

Soil

A mucky or peaty surface

horizon underlaid by peat.

Bole

The unbranched trunk

or stem of a tree.

Bolson

A depression lacking exterior drainage

in

an arid or semiand

arid region, term used in southwestern United States

Mexico.

Bonitdtion

The
the

state of well

number

being of a population,

of individuals,

cf.

as indicated

by

Ecological bonitation.

Border Dike
Ridges of earth constructed to hold irrigation water
within certain limits in a field.

Border Irrigation
Flooding areas in

fields

by the use of Border

dikes.

Border Strip

A zone

or strip surrounding a sample plot, usually given

the same treatment as the plot.

57

Bore

tidal

feet high,

wave with an abrupt front often three or more

advancing upstream in a narrow river estuary.

Boreal Forest

The forest consisting chiefly of conifers extending across

northern North America from Newfoundland to Alaska.
Boreal Life Zone

One of Merriam's life zones including northern North

America, Boreal forest and Tundra vegetation, bounded at
its southern limit by growth-season accumulated temperature
above 43 F. of 1 0,000 F. and a mean daily temperature of
64.4 F. for the six hottest weeks. Subdivided into the Arctic,

Hudsonian, and Canadian

life zones.

Boreal Period

The

from about 7500 to 5500 B. C.,

warm,
by
dry conditions; preceded by the
Preboreal period (8000-7500 B. C.) with variable climate, and
climatic period

characterized

the Subarctic period (9000-8000 B. C.) with cold, dry climate,

Sub-boreal period.

cf.

Bottom Deposits
Organic and inorganic materials deposited beneath water
and upon the original basin or channel floor.

Bottom Fauna
Animal components of the Benthos

(q. v.).

Bottomland
See Flood plain.

Boulder-clay
Unstratified clay intermixed with

by

many

glaciers, cf. Till, Drift.

Brachypterous
Refers to organisms with short wings.

58

stones, deposited

Breast Height

A height of 4.5 feet (1.3 meters) above the average ground

surface or above the root collar, diameters of standing trees

are ordinarily measured at this height. (Abbreviation is
d. b. h.).

Breccia

rock composed of angular pieces in a matrix.

Breeding (Plants, Animals)

The

application of genetics and other sciences in the

systematic improvement of a Taxon or a population.

Breeding Potential
See Reproductive potential.

Broad-base Terrace

terrace 10 to 20 inches high, 15 to 30 feet wide, with

gently sloping sides, a rounded crown, and a dish-shaped

channel on the upper

side, built to divert run-off

water along

the contour.

Broadcast Seeding
Scattering seed on the surface of the soil as contrasted to
seeding with a drill in rows. cf. Drill seeding.

Brown

Forest Soils
group of soils with dark brown surface horizons, relatively rich in humus, becoming lighter colored below,
slightly acid or neutral, with moderate amount of exchangeable calcium; commonly developed under deciduous forests

that are relatively rich in bases, particularly calcium.

Brown Podzolic

Soils
with thin mats of partly decayed leaves
above a thin, grayish brown layer containing mineral matter
and humus; overlying yellow or yellowish brown acid B

group of

soils

horizons; developed under deciduous or mixed deciduousconiferous forests in cool temperate, humid regions.

59

Brown

Soils

group of

soils

with brown surface horizon, becoming

lighter in color with depth; accumulation of calcium carbonate at depth of one to three feet; developed under grassland
and shrubs in temperate to cool semiarid climate.

Browse
Twigs or

(1)

shoots, with or

shrubs, trees, or

woody

without attached

leaves, of

vines grazed by livestock. (2)

To

graze plant parts as in (1).

Browse-line

marking the height to which browsing animals

have removed the Browse from shrubs, trees, or vines.
line

Bruckner Cycle

The

cycle of about 35 years in average length (25 to 50

which includes an alternation of a warm dry period

years)

and a cold damp period.

Brushland

An

area characterized by shrubby vegetation.

Brush Matting

matting of branches placed on eroded land to conserve moisture and reduce erosion while trees or other vegetation is being established. (2) A matting of mesh wire and
(1)

brush used to retard streambank erosion.

Brush Pasture

A pasture with a natural cover of trees and shrubs,

where
a large part of the forage secured by livestock comes from
browsing woody plants.

Bryocole

small animal such as a tardigrade, rotifer, and nema-

tode which live

among moss

plants.

Bryophyte

plant in the phylum Bryophyta comprising mosses,

liverworts, and hormvorts.

60

Budding

(1)

amount

form of

grafting,

of tissue at

its

by inserting a bud with a small

base into a

slit

made

in the stem of

form of asexual reproduction in which

the stock plant. (2)
a new cell grows out from the parent cell, e.g., yeast plants.

Buffalo

Wallow

A depression

made by

in grassland

buffalo or cattle while

trampling or wallowing, followed by denudation and

loss of

soil.

Buffering

The

modification of environmental conditions by vegetae.g., shading, cf. Reaction.

tion or topographic features,

Buffer Species
A plant or animal which may provide an alternative food
for another animal and thus reduce the demand for certain
food items.

Buffer Strip

strip of grassland or other erosion-resistant vegetation

planted on the contour between or below cultivated strips

or fields.

Zone
An area

Buffer

or strip surrounding a study-area or other

in
area
specific
part or entirely to protect the inner area from
ecological disturbance by influences from the outside. (2)
(1)

owned range area adjoining a privately owned

range tract, which may be used to supplement the range
publicly

on the

latter.

Bulbil

small bulb or modified bulb by which the plant

is

propagated.

Bulk Density

The mass or weight of oven-dry (100-1

of bulk volume, including air space.
61

10C.)

soil

per unit

Bunch Grass

A grass which forms a tuft or bunch, many stems arising

from the root-crown in a dense mass, e.g., orchard grass,
bluestems.

Bunt Order
Rank of dehorned

cattle in a herd,

determined by aggres-

sive behaviour.

Buoyancy Theory
An explanation of

the role of morphological features that

decrease the rate of sinking of plankton.

Buried Soil
One or more

which was formerly at the

surface followed by covering with ash, sand, or some other
form of deposition.
layers of soil

Burn Scar

it

on a tree where the tissues were damaged by fire,

be
may
partly or entirely covered by later-formed tissues.
scar

Bush
(1)

a shrub.

(2)

An

especially in Australia
uncleared land.

area covered by shrubs or forest,

and South

Africa; also used for any

Butte

An
flat top,

isolated hill with steep sides and a comparatively

smaller than a Mesa, term used in western United

States especially.

Buttress

lateral plank-like extension near the base of

gives additional support to the tree.

62

some

trees,

Caatinga

type of vegetation consisting of thorn scrub in northeastern Brazil.

Cactoid
Resembling a

cactus, e.g.,

Euphorbia

spp. in northern

Africa.

Caenogenesis
young stages of an
environmental conditions, which are more recent

Special adaptations of embryonic or

animal to

in evolution than adaptations in the adult,

larvae with special spiracular openings,

cf.

e.g.,

mosquito

Deuterogenesis.

Caingin Clearing

An

area

denuded

of vegetation

and used

for agriculture

in southeast Asia.

Cairn

pile of stones used as a

landmark.

Calcareous
Refers to material containing calcium in moderate to
large amounts, especially soil with calcium carbonate,

63

Calcareous Ooze
Partially decomposed, soft, organic material mixed with
a considerable proportion of calcareous material on the bottom of some bodies of water.

Calcicole

An organism, usually a plant, growing in soil rich in

calcium.
Calcification

A soil process in which the surface soil is supplied with

calcium by the decomposition of plants or in which a
calcareous layer

is

formed in the

soil. cf.

Podzolization.

Calcifuge

plant that grows best in acid

soil.

See Acidophilous.

Calciphile

A plant that grows best in calcareous soil. See Basophilous.

Caiciphobe

An Acidophilous

(q. v.) plant.

Caldera

large basin-like depression with steep sides in the top

of a volcanic mountain, e.g., Crater Lake, Oregon.

Caliche

A calcareous hardpan
applied to deposits of

in southwestern United States, also

nitrate in Chile and Peru.

sodium

Calyx
The

outer whorl of flower parts, made up of sepals,

usually green and resembling leaves or bracts, or with other
colors in

some

flowers.

Cambium

A layer of Meristem
daughter

cells;

(q. v.) cells

and the undifferentiated

used preferably for vascular

64

cambium (which

gives rise to parenchyma, secondary xylem,

phloem in dicotyledons and gymnosperms)

and secondary
and for cork

cambium.

Cambrian
Refers to the oldest geological period in the Paleozoic
about 500 million years ago.

era,

Campo Cerrado

vegetation type in Brazil composed of scattered trees

in dense grassland.

Campos
Grasslands or savanna located south of the equatorial
forests in Brazil.

Canadian Life Zone

The southern half of
Boreal

life

zone

the coniferous forest area of the

(q. v.).

Canopy
The uppermost

layer consisting of crowns of trees or

shrubs in a forest or woodland.

Canopy Trees
Trees with crowns in the uppermost layer of forest or
woodland.

Capability
See

Land

capability.

Capacity, Adaptive

The
tions of

genetically determined range (or plasticity) of reacan organism which enable it to respond in different

ways to a variety of conditions.

Capacity Formula

formula used in hydraulics to calculate the capacity

or discharge volume of a channel.

65

Capillary Porosity
The aggregate volume of small pores within the
which retain water against the force of gravity.
Capillary

soil

Water

The

portion of soil water which is held by cohesion as a

continuous film around particles and in spaces; most of it
is

available to plants.

Caprification

The

process of Pollination

by wasps in the commercial

fig plants.

Capsule

(1) A dry, dehiscent fruit consisting of several Carpels.

A
sac-like tissue surrounding an organ. (3) Organs in some
(2)

plants such as mosses in which spores are produced.

Carapace

hard case or shield covering part of the body of some

animals,

e.g.,

crabs.

Carbohydrate

An

organic

compound

and oxygen, such

consisting of carbon, hydrogen,

as sugars, starch,

and

cellulose.

Carbon Assimilation
See Photosynthesis.

Carbonate Zone

layer in the soil with a concentration of carbonates,

chiefly calcium carbonate, found especially in arid regions.

Carbon Cycle
The circulation

of carbon

from carbon dioxide in the

atmosphere into sugar by photosynthesis in plants, synthesis

of more complex organic compounds in plants and animals,

and the return by respiration or death and decay of plant

and animal tissues to carbon dioxide.
66

Carbon- 14 Dating
The use of radioactive carbon which

has an atomic mass

and an approximate half-life of 5,500 years, for determining approximately the age of soils, buried materials
such as wood, and other organic materials. See Radiation,
of 14

Radioactivity.

Carboniferous
Refers to the Pennsylvanian (Upper Carboniferous) and
the Mississippian (Lower Carboniferous) geological periods
in the upper part of the Paleozoic era, about 200-260 million years ago.

Carcinogen

substance that produces cancer.

Cardinal Points

The
north,

four chief directions of the compass; south,

and

east,

west.

Carnivore

An
bear,

animal in the order Carnivora such

and

as the dog, cat,

seal.

Carnivorous
Refers to carnivores or to plants such as the sundew that
trap and digest insects and other small animals.

Carolinian Life

One
Austral

Zone

of the divisions of the

life

Upper Austral

life

zone. See

zone.

Carotene (Carotin)

An

orange-yellow pigment, a hydrocarbon, which occurs

commonly in plants, especially in the roots of carrots, a
precursor of vitamin A.

Carpel

The

part of the flower, usually consisting of stigma, style,

67

ovary, the latter producing one or more ovules which

develop into seeds, syn. simple pistil. Two or more carpels
may be fused to form a compound pistil.

and

Can*
See Fen.

Carrying Capacity

The maximum number

(1)

of a wildlife species which

a certain territory will support through the most critical

period of the year. (2) The maximum quantity of the
Standing crop (q. v.) which can be maintained indefinitely

on an

area. (3) See

Grazing capacity.

Caruncle

(1)
protuberance, usually fleshy, near the hilum of a
seed such as the castor bean. (2)
fleshy, naked outgrowth

on the head and neck of

certain birds,

e.g.,

wattles of the

turkey.

Caryopsis

An

indehiscent, dry, one-seeded fruit in which the pericarp (ovary wall) and seed coats are united, e.g., grain of corn.

Caste

One
insects

of the kinds of specialized individuals in social

such as termites, ants, and bees, e.g. drones, workers.

Casual Species
Species which occur rarely or without regularity in a

community.

Catabolism
The aggregate
and

of metabolic processes such as respiration

digestion by which organic compounds are changed into

simpler substance's,

cf.

Anabolism, Metabolism.

Catadromous
Refers to the migration of organisms, usually
fresh to salt water to spawn, e.g., eel.

68

fish,

from

Catalepsy

The

condition of muscular rigidity in which the body

and limbs maintain the position in which they are placed.

Cotalo

An

animal derived by crossing

cattle

and

buffalo.

Catarobic
Refers to an aquatic habitat in which slow decomposition
of organic matter is taking place, organic substances are given
off into the medium, and much oxygen is used but not

enough

to prohibit the occurrence of aerobic organisms, cf.

Oligosaprobic, Polysaprobic, Mesosaprobic.

Catch Crop
A crop grown

incidentally to the main crop of a farm

and usually occupying the land for a short period; or a crop
grown to replace a main crop which has failed.

Catchment Basin

A unit watershed, an area from which all the drainage

water passes into one stream or other body of water.
Catena

group of

soils

within a specific
but with

materials

similar

soil zone,

unlike

parent
because of differences in relief and drainage.

formed from

characteristics

Cation

An ion carrying a positive charge of electricity such as

calcium, sodium, and hydrogen, cf. Anion.
Cation Exchange

The exchange
such as

added

by soil absorbing materials

calcium replacing sodium when calcium sulfate is
of cations held

to a sodium-rich soil.

Cation-exchange Capacity

measure of the

total

quantity of exchangeable cations

that a soil can hold; preferable to base-exchange capacity.

69

Catkin
See Ament.

Caudal
Refers to the

tail

of an organism.

Caudate
Refers to the possession of a

tail

by an organism.

Caulescent
Refers to a plant which has a readily perceived stem

above ground.

Cauliflorous

woody plant that produces an Inflorescence

the
trunk or one of the chief branches, e.g., the
from
directly
Refers to a

fig tree.

Catiline
Refers to the stem of a plant.

Cavernicole

An

organism that

lives in

a cave.

Cecidium

A gall

produced by an

insect or a fungus

on a

plant.

Cell

Sap
The solution

in water of organic

and inorganic substances

in the Vacuole of a plant cell.

Cellulose

The

principal

component

of cell walls of plants, a com-

plex Carbohydrate.

Cenospecies

A group of species

in nature distinguished only by factors

external to the organisms, or the various forms of a species

under domestication, a "superspecies."

70

Cenozoic
Refers to the geological era extending from 40 million
years or more ago to the present era which began about one
million years ago.

Center of Dispersal

The

Taxon has spread or

area from which a

is

spreading.

Center of Origin

The
it

Taxon

area in which a

originated and from which

has spread.

Cephalic Index

A measure of the conformation of the human head, the

breadth in percentage of the length (front to back).
Cereal

plant in the grass family, Gramineae, the grains of

which are used for human food, e.g., maize, wheat, and oats.

Seed

Certified

Seeds that have been approved by a certifying agency as

qualifying under established standards of germination, free-

dom from

diseases

and weeds, and trueness

to variety.

Cespitose (Caespitose)
Refers to plants with branches, short stems that are
usually covered with leaves, forming dense tufts or cushions.

Cestode

An

animal in the

class

Cestoda, including the tapeworms.

Cetacean

A Mammal
dolphins, and

in

the

order Cetacea,

including whales,

found especially

as bracts in flower

porpoises.

Chaff
(1)

dry, thin scale

71

heads of

many

Composites.

grains removed during

(2)

The

outer layers of cells of

threshing.

Chalk

gray or white form of limestone composed mostly of

the remains of small marine organisms, with a very high
content of calcium carbonate.

Chamaephyte
One of the classes of Raunkiaer's life-forms, consisting
of plants whose Perennating buds are located between the
surface of the ground and a height of 10 inches (25 cm.).
Chaparral

Low and often dense scrub vegetation characterized by

shrubs or dwarf trees with mostly evergreen and often hard
leaves such as oaks and buckbrush, cf. Maquis.
Character

An

attribute or property of an organism, functional or

structural, modifiable

by environmental conditions within

genetically determined limits.

Character (Characteristic) Species

The

species in classes 3, 4,

and 5 of Braun-Blanquet's

fidelity classification. Class 5 includes species

occurring exof
or
almost
in
kind
so
a
plant comclusively
particular
munity; class 4 contains species that show a strong preference
for one kind of community but occurs sparingly in others;
class 3

contains species that often occur in several kinds of

communities but the optimum growth

kind.

cf.

is

found in only one

Fidelity.

Characteristic Species-combination
A group of species in a community-type, which comprises
the Character species and other species that have a Constancy
rating above 80 per cent (varies with authors from 60 to 90
per cent).

72

Chart Quadrat

chart or

map

and area of each

of a sample area showing the location

plant.

Chasmophyte

cf.

plant growing in the crevice of rocks,

e.g.,

saxifrages,

Dam
A small low dam constructed in a watercourse

to decrease

Chomophyte.

Check

the velocity of stream flow and to promote the deposition of

eroded material.

Chemical Stratification

A condition found in temperate lakes of the second order

during the summer and winter stagnation periods in which
become different chemically from

certain horizontal strata

adjacent ones, often with abrupt transitions.

Chemosynthesis
The kind of nutrition found
energy

is

in various bacteria in which

secured from the oxidation of inorganic materials.

Chemotaxis
Movement

of

an organism

induced

by a chemical

stimulus.

Chemotrophic
Refers to an organism that obtains energy from a chemiexcluding light, e.g., sulfur bacteria, cf. Hetero-

cal reaction,

trophic, Autotrophic, Phototrophic.

Chemotropism
Growth

of

an organism in response

to

chemical

stimulus.

Chernozem

zonal group of soils with deep, dark brown to black,

organic matter, grading into lighter

fertile surface soil, rich in

73

below, and containing a calcium carbonate layer

depth ranging from 1.5 to 4 feet. Associated with tall
grassland in a temperate to cool, subhumid climate.
colored

soil

at a

Chestnuts Soils

A zonal

with dark brown surface horizons

grading into lighter colored soil below, and a calcium carbonate layer varying in depth from 1 to 4 feet. Associated with
grassland in temperate to cool and subhumid to semiarid

groups of

soils

climates, in moister regions than

Brown

soils,

drier than

Chernozem.

Chianophile

A plant that can endure long-lasting snow-cover during

winter and spring, or one that requires snow-cover in winter.
Chianophobe

plant that cannot tolerate long-lasting snow-cover, or

live with little or no snow-cover during winter.

one that can

Chill-coma

The

condition in animals caused by exposure to low tem-

perature in which most of the physiological processes have

been slowed down or arrested.

Chimera
An organ
each other,

with genetically different tissues adjacent to

e.g., a green leaf with an area of white tissue.

Chinook

warm, dry wind descending the eastern slopes of the

Rocky Mountains in North America onto the adjacent
plains, cf. Foehn. In Washington and Oregon coast country
a

warm, moist, southwest wind.

Chiseling
See Subsoiling.

Chitin

nitrogen-containing polysaccharide

74

forming a hard

Invertebrates, especially insects; found

also in the cell walls of many fungi.

outer layer in

many

Chlorenchyma Tissue
In plants Parenchyma

cells

containing Chloroplasts.

Chlorinity

The
water

is

chloride content of a solution, the average in sea19.3 per cent.

Chlorophyll

A mixture

of chlorophyll a and chlorophyll b, the green

in Chloroplasts in plants, except in the
contained
pigments

on

in chlorophyll.

protoplasmic body or plastid in the

cells of plants

blue-green algae. Photosynthesis

is

carried

Chloroplast

The

that contains the Chlorophyll.

Chlorosis

The condition of plants when chlorophyll fails to develop,

the plants are yellowish white to white arid poorly developed.
Chlorotic
Refers to a plant that has Chlorosis.

Chomophyte

plant that grows in a fissure or crevice in rock, or

on ledges where rocks have accumulated, cf. Chasmophyte.

Chondriosome
See Mitochondrion.

Chordate

An animal in the phylum Chordata, characterized by a

notochord, a dorsal central nervous system, and gill slits,
e.g., the Vertebrates.
Choripetalous

corolla consisting of separate petals, syn. polypetalous.

75

C Horizon
In soils the unconsolidated, partly weathered rock fragments from which the upper A and B Horizons (q. v.), have
developed; occasionally lacking,

Chorology
The study

of regions or areas,

cf.

cf.

horizon.

Synchorology.

Chresard

term occasionally used for the water in soil that

available to plants for absorption.

is

Chromatic!

One

of the halves of a divided

Chromosome.

Chromatin
Material in the nucleus and chromosomes which stains

deeply with certain dyes.

Chromatophore
(1)

Plastid (q. v.)

which contains pigment in a plant

Chloroplast, Chromoplast. (2) In animals a cell or

of
cells with pigment which has the capability of
group

cell, e.g.,

changing color.

Chromogenic
Refers to the capability of an organism to produce color
in a substance, e.g., certain bacteria.

Chromoplast

plastid other than a Chloroplast, containing pigment,

usually yellowish or red in color.

Chromosome
The

threadlike or rodlike bodies bearing genes in the

and animals, formed from chromatin during
the process of cell division.

cells of plants

Chrysalis
See Pupa.

76

Chubasco

Gulf of
land
and
on
Dust
whirls
California, resembling
Waterspouts
over water; reaches rather great heights and becomes violent
vortical disturbance in the vicinity of the

enough

to capsize small craft.

Chute

high-velocity conduit for conveying water to a lower

level without causing erosion because of excessive velocity
and turbulence.

ChyJocaulous
Refers to stems that are fleshy,

e.g.,

cactus stem.

Chylophyllous
Refers to leaves that are fleshy,

Chyme
A semi-fluid

e.g.,

agave leaves.

substance, the partly digested food passing

from the stomach into the duodenum.

Ciliate
Refers to a row of minute hairs along the margin of a
structure or organ of organism.

Cilia

The
a

hairlike, protoplasmic

outgrowths on the surface of

cell.

Cinereous
Refers to color that resembles ashes.

Circle of

Vegetation

All of the species and communities that are restricted, or

nearly so, to a natural vegetation unit, the highest unit of
floristic

classification

according to Braun-Blanquet.

Circulus

One

of the concentric circles or ridges

77

on a

fish scale.

Circumboreal
Refers to organisms occurring in North America and
'

Eurasia.

Circumpolar
Refers to organisms that occur in the polar regions of

both hemispheres.

Cirque

deeply eroded depression with steep slopes in areas

which have been

glaciated, syn. Corrie.

Cladode
See Cladophyll.

Cladophyll

modified stem that has the appearance and the func-

tions of a leaf, e.g., asparagus, syn. Phylloclade.

Clan

group of animals that includes several interrelated

families, or a group of plants arising from a common progenitor such as a group of young plants around the parent.
cf.

Colony.

Class

A
e.g.

unit of classification of organisms, composed of orders,

Monocotyledons, Mammals.

Clavate
Club-shaped, larger at one end.

Clavicle
A bone in the shoulder girdle of many vertebrates.

Clay
Small mineral particles of the

than 0.002
mm. in diameter. (2) Soil material that contains 40 per cent
or more of clay particles, less than 45 per cent of sand, and
less than 40 per cent of silt.
(1)

78

soil,

less

Clay

Loam

Soil material that contains 27

particles

and 20

to

40 per cent of clay

to 45 per cent of sand, the rest of

silt.

Claypan

compact and relatively impervious clay, not

cemented, but hard when dry and plastic or stiff when wet;
layer of

similar to a true hardpan in that it may interfere with the

movement of water or with the development of roots.

Clean Tillage
Cultivation of a field to prevent the growth of
except the particular kind of crop wanted.

all plants

Clear Cutting (Felling)

The

felling of all merchantable trees in

operation, cf. Selective cutting.

an area in one

Clearing
(1)

An

area of land from which trees and shrubs have

been removed.

One

of the steps in the preparation of a

tissue for microscopic observation.
(2)

Cleistogamous
Refers to Self-pollination

open,

e.g.,

some

(q. v.) in flowers that

do not

violets.

Climacteric

great change

in a physiologic process,

e.g.,

a pro-

nounced rise in the respiration rate at about the time that

some fruits such as the apple are picked, or the menopause
in

human

beings.

Climagraph
See Climograph.

Climate

The

aggregate of

all

atmospheric or meteorological

influ-

ences, principally moisture, temperature, wind, pressure, and

evaporation, which combine to characterize a region, cf.

79

Weather. Continental climate

is

the characteristic climate

of land areas separated from the moderating influence of

the oceans by distance or mountain barriers, marked by

and seasonal changes in temperature.

Oceanic climate is the characteristic type of climate of land
areas near oceans which have a moderating influence on the

relatively large daily

range of variations in temperature.

Climatic Climax
The Climax (q.

v.)

that develops

on land (moderately

rolling to level) that is neither excessively nor inadequately

drained in a region, so that the major environmental conditions affecting organisms are climatic, e.g., the beech-maple
forest in southern Michigan. Theoretically, the ultimate

phase of ecological development of communities that the

climate of a given region will permit, cf. Monoclimax,

Edaphic climax, Polyclimax.

Climatic Factors
Atmospheric or meteorological conditions which collectively make up the Climate (q. v.) cf. Biotic factor, Edaphic
factor, Factor ecological.

Climatic Formation
(1)

The major

temperate

climatic

vegetation type in a region, e.g., the

grassland comprising the prairie and

plains grassland in the United States and Canada, cf. Biome.

complex of communities which are geographically
(2)

linked with one another because of climatic conditions, an

extremely complex vegetation unit. cf. Climatic climax.

Climatic Region

One
on the

of the

main portions

of the earth's surface delimited

basis of Climate such as the polar, temperate, sub-

tropical,

and

tropical; each

with subdivisions.

Climatograph
See Climograph.

80

Climatology

The

study of Climates and their influences.

Climax
The kind

community capable of perpetuation under

climatic and edaphic conditions; the terminal

of

the prevailing
stage of a Sere

under the prevailing conditions. The

physi-

ographic climax is a climax determined in large measure by

the nature of the topography or soil, e.g., a forest climax on
a north-facing slope while grassland is the climax on the
south-facing slope of the same ridge. The edaphic climax
a climax determined largely by the nature of the soil
conditions, e.g., a saltgrass marsh in a poorly drained alkaline
biotic 'climax is a climax caused
depression in grassland.
is

by permanent influence or combination of influences caused

by one or more kinds of organisms, including man. cf.
Climatic climax, Succession.
a

Climax Area

A region

occupied by the same Climax.

Climax Community
See Climax.

Climax Complex
The totality of
(q. v.),

Seres that lead to a Climatic climax

occupying a large area corresponding to a Climatic

region.

Climax Formation

major Climax occupying a large area, e.g., the deciduous forest formation, cf. Climatic formation.

Climax Units
The units of

a Climatic climax

(q. v.);

Association, Con-

sociation, Society, Clan.

Climax Vegetation

A pattern or complex of

Climax
81

(q. v.) stages

correspond-

ing to the pattern of environmental gradients or habitats.

Climograph

chart in which one climatic factor such as the

mean

monthly temperature
plotted against another factor such
as the mean monthly precipitation or the mean relative
is

humidity.

Climosequence

series of climatic data for different places in

an

area.

Cline

gradation in genetic properties of a population along

an environmental gradient.

Clinometer

An

instrument for measuring the angle of a slope.

Clisere

series of different

Climaxes

(q. v.) in

a particular area

resulting from changes in climate, e.g., the succession of

climaxes during post-glacial time in north central United
States.

Cloaca

The

terminal portion of the gut into which reproductive

and kidney ducts open, as for example in most Vertebrates

such as birds,

amphibians,

reptiles,

and many

fishes.

Clod

A mass of soil

produced by plowing or digging.

Clonal
Refers to a clone.

Clone
The progeny produced
Parthenogenesis, from a

vegetatively, by Apomixis, or by
ancestor, cf. Ortet, Ramet.

common
82

Closed Community
A Community in which

the Niches are so well occupied

by organisms that invasion by other organisms is difficult or
impossible.

Closed Society

Society (q. v.) in which strangers are rarely admitted,

many kinds of insect societies including bees.

e.g.,

Cloudburst

A
cially

sudden and extremely heavy downpour of

in mountainous regions.

rain, espe-

Cloud Forest

A forest occupying the parts of mountainous regions

where cloudiness or moisture condensation occurs regularly,
e.g.,

laurel forest in the

Cloud Seeding
The placing

Canary

Islands.

of materials such as silver iodide in the

clouds to produce precipitation.

Clutch

The

aggregate of eggs or the young of birds.

Coaction

An

Interaction (q.

v.)

among

organisms,

e.g.,

Competi-

tion, Cooperation, Symbiosis.

Coadaptation
The correlated

modification of two or

more mutually

dependent organs or organisms, e.g., the structure of a

flower and the proboscis of an insect.

Coastal Plain

A
low

plain between the sea and higher land, usually at a

altitude.

83

Coccidosis

A disease in poultry, rabbits, etc., caused by certain microorganisms (Sporozoa).

Codominant
One

of two or

more

of the dominants in a community.

Coefficient of Association
A measure of the joint occurrence of any two species not
due to chance, obtained by dividing the number of samples
in which both species occur by the number of samples in
which it is expected they would occur only by chance.
Coefficient of

The

Community

ratio of the

number

of species

munities or areas to the total

in each of the communities,

cf.

number

common

to

two com-

of species occurring

Index of

similarity.

Coefficient of Variation

The

standard deviation expressed as a fraction of the

mean, or as a percentage.

Coelenterate

An
corals,

animal in the Invertebrate phylum Coelenterata,

sea-anemones,

Coelom
The body

e.g.,

jellyfish.

cavity in
of
animals.
groups

many

invertebrate

and vertebrate

Coenobiology (Cenobiology)
See Biocoenology.

Coenobium

colony of organisms held together in a

stance, e.g., Volvox.

common

sub-

Coenocline

The

sequence of natural communities in relation to

84

environmental gradients; the distribution of natural communities in an Ecocline (q. v.).

Coenocyte

group of protoplasmic units; a structure with many

nuclei and no cross walls as occurs in a number of algae and
fungi.

Coenospecies

A group

of Species in which hybridization

is

possible, cf.

Superspecies, Syngameon.

Coffer-dam

barrier constructed in a

body of water
is
pumped,

an enclosure from which the water

so as to

form

to

permit free

Savanna of cogongrass (Imperata

spp.) in the

access to the area within.

Cogonal

An

artificial

Philippines.

Col

A high pass

in a

mountain range.

Colchicine

An
autumn

alkaloid that inhibits Mitosis, obtained from the

crocus (Colchicum autumnale), used to produce

polyploidy

artificially.

Cold-air Drainage

The
less

settling of cold air in low places displacing the

warm air, as at the mouth of a mountain canyon.

dense

Cold Desert
Land covered with snow and

ice.

Cold Front

The boundary

of a mass of cold air

air.

85

and a mass of warm

Cold Hardiness (Resistance)

The

capacity of an organism to tolerate low temperatures.

Coleopteron

An

insect in the order Coleoptera, the beetles.

Coleoptile

The

sheath surrounding the Plumule in the early seedling stage of plants in the grass family.

Coleorhiza

The

sheath surrounding the Radicle in the early seedling

stage of plants in the grass family.

Collembolon

small primitive insect in the order Collembola, the

springtails.

Collenchyma
Elongated,

living
mostly in the corners,

cells

with

common

walls

usually

thickened

in stems of herbaceous plants.

Colloid

substance in the colloidal state in which the dispersed

particles are larger than those in a true solution, ranging

from 0.001 to

0.1

micron in diameter.

Colluvium
Mixed deposits

of soil material near the base of rather

steep slopes, accumulations from

action, and local wash.

Colon
The

slides,

soil

creep,

frost

part of the large intestine excluding the rectum, of

Vertebrates.

Colonial
Refers to organisms that form Colonies

86

(q. v.).

Colonization
Occupation of an area by a group of organisms,

cf.

Invasion.

Colony

A group of individuals of one species, with a more or less

permanent

location, e.g., a prairie

Columnar Structure
The arrangement of

dog "town."

soil particles in

blocky pieces with rounded tops.

cf.

elongated, vertical,

Soil structure.

Combination of Species, Characteristic

See Characteristic combination of species.

Commensal
One

of the organisms reacting in Commensalisrn (q.

v.).

Commensalism
The

living together of two or more organisms with benefit

usually to one and with injury to none. cf. Symbiosis,

Coaction.

Commensurabiiity

measure of the extent to which ranches should share

on nearby public land or cooperatively

controlled range, as determined by the forage resources of
the privately controlled property of the ranches involved.
in grazing privileges

Community

A group of one or more populations of plants and animals

in a

common

in a broad

spatial arrangement; an ecological unit used

sense to include groups of various sizes and de-

grees of integration, cf. Association, Biocoenosis, Concrete

community, See Stand. An Abstract community or Community-type

is

an assemblage of

community-type,

cf.

stands, e.g., the oak-hickory

Association.

Microcommunity

is

community or stand occupying a small area such as an area

87

of mosses between clumps of grass and a Microcommunitytype consists of an assemblage of microstands. cf. Closed

community.

Community Complex

mixture of concrete communities or Stands, including

transitional stands, e.g., a sand-dune complex.

Community Dynamics
The

aggregate of changes that take place within and between communities, cf. Succession, Syngenetics, Fluctuation.

Community Mosaic
The arrangement

of two or

more microstands making up

the plant and animal life of an area, such as the different

kinds of vegetation on the mounds and in the depressions in

a marsh or bog.

Community Regulation
See Homeostasis.

Community-type
(1)

See Abstract community. (2) -A group or class of

similar abstract communities.

Companion

(Species)
According to Braun-Blanquet's Fidelity classification the
species of plants that are not restricted to any definite kind
of vegetation unit.

Companion Crop

A crop which

is

grown with another

crop, usually applied

to a small grain crop ("nurse crop") with which forage crops
are sown.

Compatibility

The

capacity of two organisms to crossbreed successfully.

Compensation Intensity
The intensity of light at which
88

the

amount

of oxygen

produced by Photosynthesis of a plant equals the oxygen

absorbed in Respiration.

Compensation Level (Point)

The depth in a body of water at which

the Compensation

intensity of a given plant occurs.

Competition
The condition

that exists

when

the requirements of one

or more of the organisms living in a community cannot be

obtained from the available supply of resources, cf. Exploitation, Interference.

Competitive Exclusion Principle

A generalization "that states

two similar species rarely

if

that as a result of competition

ever occupy the same ecological

Niche. Also termed Cause's principle, Grinnell's axiom.

Competitor

An

organism competing with one or more other organ-

isms.

Complementary Genes
Two or more genes that by

their joint action produce a

character.

Complete Flower

flower that has

stamens, and one or

all

more

of the usual parts; sepals, petals,

pistils.

Complex
See

Community complex.

Complex Gradient

A gradient comprising a mixture or a combination of

environmental conditions, cf. Ecocline.
Composite

plant in the family Compositae,

89

e.g., aster,

sunflower.

Compost

pile of decomposing organic matter of plant or animal

origin in which soil or other amendments such as lime, nitro-

gen,

and phosphorus may be mixed.

Concealing Coloration
Color of plumage, pelage, scales, scutes, skin, or other
body covering which brings about some degree of conformity
in the appearance of an animal with its biotic or inanimate
environment.

Concentrates
Feed
and low

that has a high content of total digestible nutrients

fiber content, e. g., grain and grain by-products.

Conditioned Reflex
See Reflex.

Conditioner

A
terial

substance that modifies the characteristics of a ma-

or

medium

to

which

it is

added.

Condition Factor

numerical index, usually applied only to fishes, which

represents the relationship between length and weight of the
animal.

Conditioning, Environmental

The

modification of the environment of one or

ganisms by
tions,

e.

g.,

more

or-

their activities including Reactions and Coacliberation of oxygen by water plants in an

aquarium.

Conductivity

The

total electrolytic

mined by measuring the

content of natural waters, deterelectrical conductivity.

Congelifraction

The

splitting of rocks caused

90

by

frost.

Congeneric
Refers to plants or animals in the same genus,
Quercus alba and Q. rubra.

e.

g.,

pine, spruce,

fir,

Conifer

Any
juniper,

plant in the order Coniferales,

e. g.,

etc.

Coniferous
Refers to a Conifer, or to the order, Coniferales.

Conjunctive Symbiosis
See Symbiosis.

Conservation
Usage or the aggregate of practices and customs of man
that permit the perpetuation and sustained yield of renewable resources and the prevention of waste of non-renewable
resources.

Consociation
In the Clements usage a morphological part of a Climax
Association, characterized by the presence of one dominant,
e. g., the little bluestem and
needlegrass consociations in
climax tall grass or true prairie.

Consocies
In the Clements sense a morphological part of an Associes (q. v.), a developmental unit, characterized by the
presence of a single dominant, e. g., a stand of Russian thistle
in the

first

weed

stage in secondary Succession.

Consortism
See Symbiosis.

Constance
See Constancy.

Constancy
The percentage

of occurrence of a species in the total

91

number

of plots, uniform in area, located in a

number of
commun-

stands of one kind of Community-type or Abstract

ity, cf. Presence.

Constants of a Community or Association

The

stancy (q.
varies

which show the highest degrees of Conthe most usual lower limit is 80 per cent, but

species
v.);

from 50

to 90 per cent, according to various schools.

Constructive (Species)
Refers to plants whose Reactions or Coactions aid

in the

development or persistence of a Community.

Consumer Organisms (Consumers)

Organisms which ingest other organisms or food particles, may be classified as primary, secondary, etc., depending

upon

Trophic

their position in the

Consumptive Use
The quantity of water
plus the

Food chain

(q. v.)

or the

level (q. v.). cf. Producers.

amount

lost

used and transpired by vegetation

by evaporation,

syn. Evapotranspiration.

Contagious Dispersion

The non-random

(above normal) occurrence of indi-

viduals of a species, forming aggregations, syn. over-dispersion, Hyperdispersion. cf. Normal dispersion, Hypodispersion.

Continental Bridge Hypothesis

The

hypothesis that the present-day continents were

once connected by isthmuses, or other areas of land.

Continental Drift Hypothesis

The hypothesis, advanced especially by Wegener, that

the presentnday continents were displaced horizontally from
the original mass of land to their present positions.
92

Continental Platform

The

parts of the world comprising the lower areas of con-

and the continental shelves

tinents

(q. v.).

Continental Shelf

The

shallow, gently sloping portion of the seabottom

bordering a continent, down to a depth of about 100 fathoms.

Continental Slope

The

steeply sloping portion of the sea-bottom extending

seaward from the Continental

shelf.

Continuous Grazing
The practice of grazing

the vegetation of an area without

interruption throughout the season, cf. Deferred grazing,

Rotation grazing.

Continuum (Vegetation and Animal Life)

The occurrence of populations of organisms

along a

gradient, forming a distribution pattern of intergrading populations.

Contour
(1)

An

imaginary line on the surface of the land which

connects points of the same altitude. (2) A line on a

to show the location of points of the same altitude.

Contour Farming
The performance
ing,

map

of farming operations such as plow-

seeding, and cultivating along contour

lines.

Contour Furrows
Furrows located along contour lines on range or pasture
land to prevent or retard runoff and permit the infiltration
of water into the soil.

Contour Interval
The vertical distance between two contour
93

lines.

Contour Strip Cropping or Farming

The growing of crops on the strips between contour

lines,

at right angles to the slope. Strips of grass or other plants

may

con-

be grown in alternation with the cultivated crops.

servation practice to control or eliminate runoff
and permit greater infiltration of water.

and

erosion,

Control Factor

The

chief limiting factor or condition influencing an organism, e. g., wilting of a plant caused by insufficient soil
water.

Control Flume
An open conduit or

artificial

channel arranged for meas-

uring the flow of water.

Controlled Burning
See Prescribed burning.

Convergence
The increase

in similarity of different Seres as Succession

proceeds from early to

late stages.

Convergent Evolution
The development of similarity

in characteristics of or-

ganisms that were originally more different.

Cooperation

The
ficial

kind of reaction between organisms which are bene-

and non-obligatory

to those participating,

cf.

Disopera-

tion, Protocooperation, Coaction.

Copepod
An animal
in salt

and

in the order Copepoda,

minute Crustaceans

fresh water.

Coppice

A grove

in which the trees are regularly cut,

arising from the base.

94

new growth

Copraphagous
Refers to organisms that feed on dung.

Copse
See Coppice.

Coral Reef

formed chiefly by corals,

or near the surface in some warm parts of

series of calcareous rocks

partly by algae, at
the sea.

Cordillera

A system of mountain

ranges,

e. g.,

the Andes Mountains

in South America.

Coriaceous
Refers to structures that are leathery such as leaves.

Corm

short, firm, enlarged, fleshy

the crocus.

underground stem

as in

Cormophyte

plant that has a stem and roots,

cf.

Thallophyte.

Corneous
Refers to a structure that

is

horny in texture.

Corolla

The whorl of parts, usually colored, of a flower,

of petals, within the calyx.

composed

Corraision

The
terial

gravel

process by which flowing water carrying solid mawears away underlying rock, e. g., a stream carrying

and sand.

Corridor

A broad, continuous land connection enduring a long

time and thus permitting the extensive interchange of or^

95

ganisms by migration as at the present time between Asia

and Europe, cf. Filter bridge, Sweepstakes bridge.

Coteau

series of

Moraines, a term used in Western United

States.

Coterie

A closed social group of animals,

fend their

common

territory

individuals of which de-

against

members

of

other

coteries.

Cotyledon

primary leaf of the embryo in seeds, only one in the

Monocotyledons, two in Dicotyledons. In many of the latter
such as the bean they emerge above ground and appear as
the

first leaves.

Cover
(1) The plants or plant parts, living or dead, on the surface of the ground. Vegetative cover or herbage cover is composed of living plants, litter cover of dead parts of plants.
cf.

Basal area.

one or more

(2)

The

area of ground covered by plants of

species.

Cover, Vegetation

The
in

an

area of ground covered by the

sum

total of plants

area.

Coverage
The percentage

of the area of a

community covered by

a plant or an animal that is attached to the substratum, as

seen from above, cf. Cover.

Cover Crop

crop growing close to the ground for the chief purof

pose
protecting the soil from erosion and also for the
improvement of its fertility, between periods of regular pro-

96

duction of the main crops, or between trees and vines in

orchards and vineyards.

Covert

A place

of concealment for an animal,

Cover Type
The present

vegetation on an area, a
ing the Cover at the present time.

e.g.,

a hedge row.

community form-

Cow Month
The

quantity of feed or forage required for the maintenance of a mature cow in good condition for 30 days. cf.

sheep month.

Creche

group of young animals

after leaving their nests.

Creek

stream that

is

intermediate between a river and a

brook.

Creep, Soil

The

slow,

downward, mass movement of

soil

on a

slope.

Crepuscular Periods

The

periods of dusk before sunrise and after sunset,

Auroral, Vesperal, Diurnal, Diel, Nocturnal.

cf.

Cretaceous

The most

recent geological period of the Mesozoic era,

which began abont 135 million years ago and lasted for about
60 million years.

Critical Factor
See Limiting factor.
Critical Slope
See Angle of repose.

97

Cropland
Land

used regularly for the growing of crops (exand permanent pasture). Includes orchards,
cultivated summer fallow, rotation pasture, and land that
is temporarily idle but customarily used for production of
that

is

cept forest crops

crops.

Crop Residue
The parts of

plants, or a crop, left in the field after harthe

desired
vesting
part such as grain or fruit, e. g., Stubble.

Crop Rotation
The growing

of different crops in recurring succession

piece of land.

on the same

Crop, Standing
The total amount

of organic material of one or more

species in a certain space at a given time; e. g., the trees in
a stand that are useful for lumber or other products, cf.

Biomass.

Cross
See Hybrid.

Cross-fertilization
Sexual reproduction by means of two separate organisms,
cf.

Self-pollination, Cross-pollination.

Crossing-over

The

interchange of parts of Chromatids (q. v.) of

mologous chromosomes during pairing in Meiosis.

Ho-

Cross-pollination

The
one

transfer of pollen from the anther in the flower of

plant to the stigma in the flower of another plant. Syn.

Xenogamy,

cf.

Self-pollination.

Cross-timbers
Strips of

in

oak

forest at right angles to the river systems

Oklahoma and Texas.

98

Crown Canopy
See

Crown

Crown
The

cover.

Class
trees

occupying a similar layer or position in the

crown cover such as the dominant crown class consisting of

dominant trees in the canopy layer; co-dominant crown class,
trees with less well developed crowns but in the canopy
layer; intermediate crown class, trees with crowns mostly
below the canopy layer but extending into it; and overtopped
crown class, trees with crowns entirely below the canopy
layer,

crowns poorly developed, or

trees are suppressed, dying,

or dead.

Crown Cover
The canopy formed by

the trees in a forest.

Crown Density
The
plete

percentage of the total area of land that has a com-

crown

cover.

Crucifer

plant in the mustard family, Cruciferae,

e. g.,

radish.

Cruise

A survey of forest land to locate and estimate the volume

and grades of the standing timber; or an estimate secured
in such a survey.

Crumb
The

Structure
condition of a

and highly porous

soil that

contains irregularly shaped

aggregates.

Crustacean

An Arthropod
Crustal

in the class Crustacea,

e. g.,

crab, shrimp.

Movement

movement

of the outer solid part of the earth such as

an earthquake.
99

Cryophyte

alga,

plant growing on snow or

Chlamydomonas

ice, e. g.,

"red snow," an

sp.

Cryoplanation
Land erosion or reduction by

intensive frost action.

Cryptogam

A plant in any of the groups; Thallophytes, Bryophytes,

and Pteridophytes. cf. Phanerogam.
Cryptophyte

A plant in one of the Life-form classes of Raunkiaer in

which the buds are covered with soil or water; includes
Geophytes, Helophytes, and Hydrophytes (q. v.).
Cryptozoic
Refers to animals living in darkness as under stones or in
caves.

Cucurbit

plant in the gourd family, Cucurbitaceae,

e. g.

squash,

cucumber.

Cuesta (Spanish)

kind of ridge with a gentle slope on one side and a

steep slope

on the

other.

Culled Forest

cut-over forest from which only certain individuals

or species have been removed, e. g., a forest culled for pines
of a certain minimum diameter.

Culm

stem, especially the grass stem with nodes

nodes.

and

inter-

Cultch

Empty

shells

and other kinds of material dumped into

100

spawning areas

to provide a suitable substratum for

growth

of oysters.

Cultigen

plant or a group of plants that

cultivation so far as

is

known,

e. g.,

is

grown only under

cabbage,

cf.

Indigen.

Cultivar

strain, variety, or race which originated and

tained under cultivation; not necessarily a species.

Culture

is

main-

Community

Community brought about by man's activity, e. g., a

seeded meadow; or a natural community greatly altered by
man.

cf.

Hemerocology, Secondary succession.

Curie

The basic measure or unit of radioactivity of a substance,

the disintegration of a Radioactive Isotope at the rate of 3.7
times 10 10 atoms of material per second.
Cushion Plant

An

herbaceous perennial plant that produces a form with

a dense mass of short stems and many leaves.

Cuticle

covering of fairly water-proof material composed of

Cutin in higher plants, or chitin and/or protein in many

animals.

Cutin

mixture of waxlike materials forming the Cuticle of

higher plants.

Cut-over Forest

A forest from which some or all of the merchantable trees

have been removed,

cf.

Culled

forest, syn.

101

Logged-over.

Cybernetics

The
tems in

study of kinds of communication and control

beings and in machines.

sys-

human

Cycle (Population)

The

regular or approximately regular oscillation in the

abundance of a population or species. An Intrinsic cycle is

caused by the interactions within populations of one or more

species, an Extrinsic cycle is caused by changes in the physical
or biotic environment.

Cycle of Erosion

The

changes brought about by erosion from youthful to

mature to old-age Topography.

Cyclomorphosis
The change in form

of

some animals in accord with the

season of the year as occurs in Cladocera.

Cyclosis

The

streaming of Cytoplasm in plant

cells.

Cytogenetics

The combination

of Cytology

and Genetics in the study

of variation in organisms.

Cytology
The study

of cells of organisms, a branch of biology.

Cytolysis

The

disintegration of a

Cytoplasm
The Protoplasm

cell.

of the cell excluding the Nucleus.

Cytotaxonomy
The combination

of Cytology

study of classification of plants.

102

and Taxonomy in the

Damping-off
The sudden

wilting and death of seedling plants, caused

by microorganisms.

Day-degrees
The sum of degrees of heat above a threshold, such as the
sum of the degrees above a daily mean of 43 F. for the growing season, or for some other period,
mation.

cf.

Temperature sum-

Day-neutral Plant

plant that blooms when the length of day

or
short, cf. Photoperiodism.
long

is

either

D. B. H.
See Breast height.

DDT
An

Insecticide (q.

v.),

dichloro-diphenyl-trichlorethane.

Dealkalization
Removal by leaching or by chemical treatment of
changeable sodium from the soil. cf. Alkali soil.
103

ex-

Decapod
An animal

in the order Decapoda, class Crustacea,

e. g.,

lobster, crab, shrimp.

Decidulignosa
Communities

consisting of trees or shrubs with deciduous

leaves.

Deciduous
Refers to the losing of parts of an organism such as leaves
of trees or antlers of deer at certain seasons.

Decomposer Organism

An

breaks

organism, usually a bacterium or a fungus, that

the bodies or parts of dead plants and animals

down

into simpler compounds.

Decreaser

species that decreases in Population density or

cf. Increaser.

Cover

under continued grazing,

Deferred Grazing

The postponement

in the grazing of vegetation after

a certain stage of development has
has
started
until
growth
been attained in order to promote vigor of the plants, cf.

Continuous grazing, Rotation grazing.

Deficiency Disease

A disease or malfunctioning of an organism caused by the

lack or insufficiency of

some food substance such

as a certain

vitamin or a mineral.

Deflocculation

The separation of soil aggregates containing clay into

individual particles.
Degradation (Soil)
The change in a

soil

that occurs in leaching,

Chernozem into a Podzol.

104

e.

g.,

Dehiscent
Refers to a structure that breaks open at maturity,
a pea pod. cf. Indehiscent.

e. g.,

Deme
One

or more populations of a Taxon, an interbreeding

population.

Demography
The

study concerned with the analysis of populations in-

cluding births, deaths, age,

Dendrochronology
The dating of events

etc.

or historical periods by the study

of growth rings of trees.

Dendrology
The study of

trees.

Denitrification

The change
teria in

which

of nitrogenous

free nitrogen

is

compounds by

certain bac-

formed.

Density (Population, Species)

The number of individuals in

relation to the space in

to

which they occur, refers to the closeness of individuals

one another, cf. Population density, Abundance, Cover.

Density-dependent Factor

An influence that is dependent upon a certain density

of individuals in order to be fully effective, e. g., a limited
number of prey animals for the number of predators present
in an area.
Density-independent Factor

An

is effective without
regard to the denindividuals in a population, e. g., very unfavorable
weather such as a blizzard. According to Andrewartha (1954)

influence that

sity of

and Birch

this factor

is

non-existent. See Non-reactive factor.

105

Denudation
(1) The processes by which

the surface of the earth

is

worn away, including rainfall, wind, erosion, waves, tides,

frost action, heating by the sun, etc. (2) The total destruction
of plant and animal life in an area by physical or biotic
means.

Dependence

relationship between organisms in which one organism

receives benefit from the other, not reciprocal, cf. Competition, Symbiosis, Coaction.

Dependency Zone (Range)

certain area surrounding -an area of private land,

within which the use of the private land may be supple-

mented by use of the

public' land.

Dependent Property (Range)

Privately owned or controlled land or water judged to
have special claims for companionate use with certain public
or cooperatively controlled range land.

Deposits
See Allochthonous, Autochthonous, Terrigenous.

Depth, Effective Soil

The depth

of the soil

readily to obtain water

which roots of plants can penetrate

and plant nutrients, cf. Working

depth.

Desalinization
Removal of salts from a

saline soil, usually

by leaching.

Desert

An area of land which has an arid, hot to cool climate,

with vegetation that is very sparse and usually shrubby.
Deserta
Various kinds of vegetation found in areas and on subpoor in available water for plant growth such

strata that are

106

as

dry deserts,

salt deserts,

cold deserts, strand vegetation,

dune communities, and rock communities.

Desert Grassland

The
and

extensive grassland in southwestern United States

Mexico, characterized in part by several species of grama-

grass,

three-awn

grass,

and curly mesquite.

Desert Pavement
stony or pebbly surface of land after the fine mahave been removed by wind or water action.

The
terials

Desiccation
See Siccation.

Desilting

Area

An

area occupied by vegetation such as grasses or shrubs

used solely for the deposition of silt and other debris from

flowing water, located above a reservoir, pond, or field which

needs protection from accumulation of sediment.
i

Desilting Basin
See Settling basin.

Detention

Dam

A dam

built for the purpose of storing streamflow or

surface runoff, and to control the release of such stored water.

Deuterogenesis

The development
of the life-cycle,

e. g.,

of adaptive characteristics in late stages

wings of insects, cf. Caenogenesis.

Devonian

A geological period in the Paleozoic era, which began

about 325 million years ago and lasted about 45 million
years.

Dew-point
The temperature
of holding

at which a certain body of air is capable

no additional water vapor, so that any decrease

107

in temperature or any increase in water vapor will result in

condensation of the vapor into liquid water; at this point

the Relative humidity (q.

tion deficit (q. v.) is zero.

v.) is

100 per cent and the Satura-

D Horizon
The

stratum in the

composed
terials,

soil

below the depth of weathering,

and unconsolidated parent ma-

of undifferentiated

immediately below the C horizon,

cf.

horizon,

horizon.

Diameter Breast High

See Breast height.

Diapause

A period of suspended growth or development and reduced metabolism in the life-cycle of many insects, in which
the organism is more resistant to unfavorable environmental
conditions than in other periods.

Diaspora

portion of a plant such as a seed, spore, bud or other

and can give rise to a new

part that undergoes dispersal

plant,

cf.

Disseminule.

Diastrophism
Dislocation of the earth's crust such as folding, resulting
in the formation of mountains, sea basins, etc.

Diatom

A one-celled, microscopic alga in the

with siliceous walls.

class Bacillariaceae,

Diatomaceous Earth

deposit of the siliceous remains of diatoms.

Diatomaceous Ooze
Material consisting of siliceous remains of diatoms found
in cold seas.

108

2, 4-Dichiorophenoxyacetic Acid (2, 4-D)

compound used to destroy undesirable plants, applied
as a dust or spray to the foliage.

Dichogamy
The maturing

of stamens

and

pistils of

a flower at dif-

ferent times.

Diclinous (Diclinic)
Refers to plants that have stamens and pistils in separate
Monoecious, Dioecious, Monoclinous.

flowers, cf.

Dicotyledon

Vascular plant in the subclass Dicotyledoneae, class

Angiospermae (flowering plants), which have seeds contain-

ing two seed-leaves or cotyledons,

e.

g.,

peas,

beans,

cf.

Monocotyledon.
Die!
Refers to the 24-hour period of day and night,
urnal, Nocturnal, Crepuscular.

cf.

Di-

Differential Species (Differentiating Species)

A species, because of its greater Fidelity (q. v.) in one
kind of community than in other kinds can be used in distinguishing vegetation units.

Differentiation

The development

organ, or immature organism into a mature organism. (2). The development of

different kinds of organisms in the course of evolution.
(1)

of a

cell,

Digestion

The

conversion of complex, usually insoluble organic

substances into simpler and usually soluble compounds by

enzymes.

Dihybrid (Cross)

An

organism resulting from the breeding of parents that

109

differ in

stems,

two characters such

cf.

as color of flowers

and length of

Monohybrid.

Dimorphism
The state of

organs of a plant or animal or individuals

in a population occurring hi two forms or colors, e. g., a
plant with leaves of two forms, cf. Polymorphism.

Dinoftagellate

A motile organism

hi the class Dinophyceae of the

of
abundance
some
forms ("red tides") along
great

causes death of

many

algae;
coasts

fish.

Dioecious
Refers to plants with pistillate and staminate flowers in
separate plants, e. g. willows, cf. Monoecious. Diclinic. In

animals refers to unisexual organisms,

cf.

Hermaphrodite.

Diploid
Refers to the presence of chromosomes in pairs or in two
sets, resulting from the union of two Gametes, each with a
single set (Haploid, q.

v.).

Dipterous
Refers to an insect in the order Diptera which possess
two wings (except parasitic forms), e. g., housefly, mosquito.

Disclimax

An enduring Climax (q. v.) community altered by disturbance by man or domesticated livestock, e. g., a grassland
which has replaced a deciduous

forest, cf.

Plagioclimax.

Discontinuity

The

existence of a gap in the geographic distribution of

a Taxon.

cf.

Distribution, Disjunct.

Disjunct
Refers to the absence of a connection as in the geographic
Taxon or a community, cf. Discontinuity.

distribution of a

110

Disfunction
See Discontinuity.

Disjunctive Symbiosis
See Symbiosis.

Disoperation

An

interaction between organisms in which one or all

are harmed, e. g. Competition resulting in stunted growth.

Dispersal
(1)

The

actual transfer or

movement

organisms from one place to another.

movement

of a

group of organisms,

The

history of the
Migration, Establish-

(2)

cf.

of Disseminules or

ment, Spread.

Dispersion

The

pattern of Distribution of individuals of a Population, especially in regard to probability.

Dispersion

The

(Soil)

breaking

down

of soil aggregates, resulting in single

more easily a soil is dispersed

grain structure; usually the

the

more credible

Disphotic

The

it is.

Zone

depths in bodies of water where light

is

inadequate

for photosynthesis in plants but adequate for animal

Aphotic zone, Euphotic zone.

life. cf.

Displacement Theory
See Continental drift hypothesis.

Dissemination

The

by which organisms or their

parts, especially spores, seeds, or fruits are scattered, cf. Diaspore, Dis-

processes

persal, Disseminule.

Ill

Disseminule

A
persal

detachable part of a plant which

and of giving

rise to a

new

plant,

is

cf.

capable of Dis-

Diaspore.

Distribution
(1)

of a

The

Taxon

geographic range (continuous or discontinuous)

any one time. (2) The pattern of occurrence of

at

individuals of a taxon in an area such as Random or Potsson (Normal) distribution; non-random or above normal,
Contagious dispersion (Over-dispersion, Hyperdispersion);
and non-random, below normal, Hypodispersion or evenspaced.

Distribution, Center of
See Center of dispersal.

Diurnal
Refers to daytime in contrast to Nocturnal,

cf.

Diel,

Crepuscular.

Divergence

The

condition in which Seres of a similar origin become

increasingly unlike as Succession proceeds toward the Cli-

max. See Convergence.

Diversion

Dam

A dam

all

constructed for the purpose of diverting part or

of the water in a stream into a different course.

Diversity Index

The number

of species in an area divided by the

number

of individuals of all these species.

Division of Labor

The specialization of parts of an organism or members

of a species for carrying on certain processes, e. g., in birds
the wings for flying and the legs for walking, in bees the
workers and drones, in plants the various kinds of
carrying on different functions.

112

tissues for

DMA
Deoxyribonucleic acid, the chief constituent of chromosomes which apparently is the material constituting the
genes.

Doldrums
The equatorial

calm or light variable winds, low

atmospheric pressure, lying between two trade- wind belts.
belt of

Dolomite

A rock containing a high

percentage of calcium and mag-

nesium carbonates.

Domatium

small structure on certain plants, particularly on the

which forms a shelter for organisms such as insects

leaves,

or fungi.

Dominance Classes
The five groups of
Coverage

species in a classification based

(q. v.).

Dominance, Ecologic
The condition in communities
in

on

which one or more

or in vegetational strata

by means

species,

of their

number,

coverage, or size, have considerable influence or control

the conditions of existence of associated species.

Dominance, Genetic
The influence exerted by

upon

dominant character or Allele

is dominant over

e.g., redness of petals in certain flowers

white, cf. Recessive.

Dominance, Social
The determination

of the behaviour of one or more animals by the aggressive behaviour or otherwise of other individuals, resulting in the establishment of a social Hierarchy.

Dominant (Character)
See Allele.

113

Dominant

A
cf.

(Species)

species that manifests Ecologic or Social dominance.

Secondary species.

Donga

gully with steep sides or a dry watercourse, a term used

in South Africa.

Dormancy
The condition in an organ or in an organism where
metabolic processes are relatively inactive as a result of internal causes, e. g., many kinds of seeds, overwintering stages
of insects,

cf.

Hibernation, Estival, Diapause.

Double Fertilization
The process, unique

in Angiosperms, in which one male

nucleus fertilizes the egg nucleus to form the Zygote which

develops into the Embryo, and the other male nucleus joins
with two other nuclei in the embryo sac to form the Endo-

sperm,

e. g.,

in corn

and other

grasses.

Down
An

area of open, treeless upland with a thin covering of

used mostly for sheep grazing; especially the chalk hills
of southern England.

soil,

Downland
Temperate grasslands

Drainage Basin
The largest natural

in Australia

and

New Zealand.

drainage area subdivision of a con-

tinent, such as the Mississippi,

basins, cf. Watershed.

Drainage Terrace

Columbia, and Colorado

A Graded terrace constructed to have a relatively deep

channel and a low ridge primarily for drainage of a hillside.
114

Draw
A natural

depression or swale; a small natural drainage-

way.

Drift (Geology)
Material of any kind which

deposited in one area after

having been moved from another, most commonly used in
reference to glacial drift, the material deposited by glacial
action. Glacial drift includes Till (q. v.) and stratified out-

wash materials,

cf.

is

Loess, Boulder-clay, Drumlin.

Drift Barrier

An

open structure constructed

across a stream channel to

catch driftwood, such as a wire fence.

Drift Fence

fence for the purpose of preventing livestock from

going from their regular range to another, often used in connection with natural barriers.

Drift,

Genetic

Random

changes in the characteristics or attributes of

populations that are usually isolated, or in the frequencies
of certain genes, which cannot be attributed to selection, mutation, or migration, cf.

Natural selection.

Drift Ice
Portions of icebergs or

ice-floes in

the open sea outside

of the areas of pack-ice.

Drill

Seeding

Sowing seeds with a drill usually in rows that are less

than one foot apart as in seeding grains, cf. Broadcast seeding.

Drip Point

The

long, attenuate tip of

the
of
forest
Tropics.

115

many

leaves in

the Rain

Drive

The complex

and external

of internal

states

and stimuli

leading to a certain behaviour in an animal.

Driveway, Stock

land

strip of

set aside for the

movement

of livestock

from one place to another.

Drosophila

A genus

genetics,

of

order Diptera,

flies,

much used

in research in

e. g. fruit-fly.

Drought

An

extended period of dryness; usually any period of

moisture deficiency that is below normal for a specific area.

Drought Resistance
The capability of an organism
little

to survive

drought with

or no injury.

Drumlin

An

oval-shaped hill composed of glacial Drift, usually

compact and not

parallel to the

commonly with
movement of the ice when
stratified,

its

longer axis

deposition oc-

curred.

Drupe

fleshy fruit in

which the single seed is within a stony

is surrounded by a fleshy layer

inner cover (endocarp) which

(pericarp), e.

g.,

plum, cherry.

Drupelet

small drupe,

e. g.,

the raspberry fruit

is

a cluster of

drupelets.

Dry Farming
(1) Cultivation of land and other farming operations in
semi-arid or arid regions without irrigation. (2)
system of
cultivation of the land in which Fallow and Mulch are used

to absorb

and

retain

much

of the precipitation that occurs.

116

Duckfoot

An

implement with horizontally spreading V-shaped

blades which provide shallow cultivation without turning
over the surface

soil

or entirely burying crop residues.

Ductless Glands
See Endocrine gland.

Duff

general term for vegetal material in forests, including

the fresh litter and well decomposed organic material and

humus. See

horizon.

Dune

A mound

or ridge of sand piled up by the winds, comfound

where sand is abundant as along lake shores,
monly
sea shores, and in desert and semi-desert areas.

Dune Sand
(1) An area

of sand accumulated by

wind action

into

dunes or hummocks, usually free from vegetation or sparsely

vegetated and undergoing erosion and redeposition by the
wind. (2) Refers to sand that has texture size of 0.1 to 0.4
mm. in diameter which has been piled up by the wind.

Duriherbosa
Vegetation consisting of herbaceous plants whose above-

ground parts die during winter,

e. g.,

grasslands.

Durilignosa
Vegetation consisting of broad, hard-leaved Sclerophyll
trees or shrubs, e. g. chaparral, (q. v.).

Dust Mulch

A shallow

layer of loose surface soil.

Dust Whirl (Dust Devil)

small, intense, vortical disturbance, usually only a few

in
diameter, in which large volumes of dust and debris
yards

117

are carried upward; occur usually in arid

and semi-arid

regions.

Dynamic Equilibrium

system that is maintained in approximately the same

condition because of the action of opposing processes or activities proceeding at about equal rates, cf Balance of nature.
.

Dynamics, Community
See Community dynamics.
Dynamics, Population
See Population dynamics.

Dysgenic
Refers to any influence that is detrimental to the genetic
properties of a population, cf. Eugenics.

Dystrophic

A type of lake or pond which contains brown

much humic

water with

material in solution and with a small bottom

fauna characterized by pronounced oxygen consumption.

Cf. Eutrophic.

118

Ecod

habitat form; an organism showing Somatic adapta-

tions to a specific environment, not hereditable, cf.

Pheno-

type, Ecotype.

Ecesis
See Establishment, Spread, Invasion.

Echard

A term occasionally used to denote the water in the soil

below the permanent Wilting percentage (q. v.); not available for absorption by plants.
Echinoderm

marine animal in the phylum Echinodermata such

starfish,

sea-cucumbers, and

as

sea-urchins.

Echolocation

The ability of certain animals, especially bats, to orient

themselves by emitting high-frequency sounds and detecting their echoes; acoustic orientation.

Ecize

To

undergo Ecesis

(q. v.).

119

Ecocline
(1)

gradation or Cline

(q. v.) in

the adaptations of a

species that is associated with an environmental gradient, cf.

Geocline. (2)
gradation of ecosystems along an environ-

mental gradient, comprising both the gradient of natural

communities (Coenocline) and the Complex gradient of environmental conditions.

Ecological Amplitude
The range of one or more environmental conditions in
which an organism or a process can function, cf. Tolerance,
Optimum, Pessimum.
Ecological Bonitation
The estimate of the numerical abundance of an organism
in a locality or a season,

cf.

Bonitation, Biotic potential.

Ecological Efficiency
The ratio between the energy available to one or more
organisms or processes and the energy that is actually utilized.

Ecological Equilibrium
See Balance of nature, Dynamic equilibrium.

Ecological Equivalence

The

situation or condition in

which two or more

species

because of their similarity in Ecological amplitude can occupy the same ecological Niche, thus being able to replace
each other.

Ecological Equivalent
An organism which participates in Ecological equivalence
(q. v.). cf. Vicariation.

Ecological Factor

Any
the

life

part or condition of the environment that influences

of one or more organisms; often classified into A;

120

and edaphic, and biotic factors, or B;

and remote factors, cf. Limiting factor.

climatic, physiographic
direct, indirect,

Ecological Indicator
See Indicator.

Ecological Longevity

The

average length of

under stated conditions,

life

cf.

of individuals of a population

Life-span.

Ecological Niche
See Niche.

Ecological Pyramid
See Pyramid of numbers.
Ecological Race
See Eco type.

Ecological Sociology
See Synecology.

Ecological Structure
See Structure.

Ecological Succession
See Succession.

Ecological Valence
See Ecological amplitude.

Ecology

The study of the interrelationships of organisms to one

another and to the environment, cf. Autecology, Synecology,
Bioecology, Sociology, Plant sociology.

Ecophene
See Ecad.

Ecospecies

Taxon

of plants consisting of one or

121

more Ecotypes

(q. v.)

within a Coenospecies

(q. v.),

capable of reproduction,

approximately equivalent to Species (q. v.).

Ecosystem
The Community

(q. v.), including all the component

the abiotic environment, forming an
with
organisms together
e.
interacting system,
g., a marsh, cf. Biogeocenose.

Ecotone

A transition line or strip of vegetation between

two com-

munities which has characteristics of both kinds of neighboring vegetation as well as characteristics of

its

own.

cf.

Edge-

effect.

Ecotype
The smallest Taxon

or group of similar Bio types

(q. v.) within an Ecospecies (q. v.), each one adapted to a
certain combination of environmental conditions. Differences between ecotypes
ological, cf.

(q. v.)

may be

morphological, or only physiEcad.

Habitat form,

Ectoparasite

Parasite living on the outside surface of another organism, e. g., a flea. cf. Endoparasite.

Ectophagous
Refers to an organism that feeds from the outside of the
it is consuming such as a deer feeding on leaves of

structure

a plant,

cf.

Entophagous.

Ectotrophic
Refers to fungi that grow on the surface of roots,

Endotrophic, Mycorrhiza.

Edaphic
Refers to the

soil, cf.

Edaphic

Edaphic Climax
See Climax.
122

factor.

cf.

Edaphic Factor

ical,

condition or characteristic of the

soil,

or biological that influences organisms,

physical,
cf.

chem-

Biotic, Cli-

matic, Ecological factor.

Edaphology
The study

of

soils.

Edaphon
The aggregate

of organisms in the soil except the roots

or underground stems of plants, cf. Plankton.

Edge Effect
The influence

of two communities

upon

their adjoining

margins or fringes, affecting the composition and density of

the populations in these bordering areas, e. g., a forest edge
bordering a grassland, cf. Ecotone.
Effective

Temperature Range

The

range between the highest and the lowest temperature in which an organism can live. cf. Ecological amplitude,
Tolerance.

Effluent
The outflow of water from subterranean storage,

cf.

In-

fluent.

Elaioplast

A Plastid in which oil

is

formed and

stored.

Electrolyte
Salts, acids,

current,

e. g.,

or bases that in a solution conduct an

sodium chloride dissolved in water.

electric

Element
Organisms that are typical or characteristic of a certain region, but may occur outside of it, e. g., a group of
prairie species occurring in the eastern part of the United
(1)

States. (2)

See Ecological factor.

123

Elementary Species
See Ecotype.
Elfin

Forest

See Krummholz.

Eltonian

Pyramid

See Pyramid of numbers.

Eluvial Layer
See

horizon.

Eluviation
The removal of material from a soil horizon by downward or lateral movement in solution and to a lesser degree
in colloidal suspension,

cf.

Illuviation.

Emasculation
In plants the removal of anthers or flowers bearing stato prevent self-pollination. In animals the removal of

mens

sperm-producing organs.

Embryo Sac
The

structure within the ovule of a flowering plant, in

which Fertilization occurs.

Emigration

The Migration of an organism out of a locality, usually

without the probability of returning, cf. Immigration.
Encinal

A grove or forest of evergreen oaks.

Enclosure

An

area fenced to include certain kinds of animals,

cf.

Exclosure,

Encystment
The state of

an organism in which it is surmetabolism is reduced, resistance to unfavorable environmental conditions increased.

inactivity of

rounded in a protective

case;

124

Endemic

Taxon confined

to a certain country or region

and with

a comparatively restricted distribution.

Endemism
The

occurrence of endemics in an area.

Endobiophyta
The existence

of a Parasite within the

body of another

organism.

Endocrine Gland

gland in animals that produces hormones,

e. g.,

the

Pituitary gland.

Endogenous
Refers to a substance or process that originated within
an organism or a cell.

Endoparasite

A Parasite living inside of another organism,

e. g.,

a tape-

worm.

Endophyte

plant which grows within another plant such as a

fungus Endoparasite; a plant which can penetrate a rock,
e. g.,

lichen.

Endoskeleton

The

supporting framework inside the body of animals

such as Vertebrates, cf. Exoskeleton.

Endosperm
The nutritive
and which

tissue that

surrounds the growing embryo,

many kinds of

present in the mature seed in

Spermatophytes such as the grasses.
is

Endotrophic
Refers to fungi that grow within roots,

Mycorrhiza.
125

cf.

Ectotrophic,

Endozoochore

A Propagule such
by

being transported inside of

Energy Flow
The intake,

which is dispersed
an animal's body.

as a seed or a spore

conversion, and passage of energy through

organisms or through an Ecosystem

(q. v.).

Energy Transformers
Plants

and animals which convert and pass on energy,

secured from sunlight by plants, from one or-

originally
ganism to another as in a food-chain,

cf.

Energy flow.

Entomophilous
Refers to plants that are pollinated by insects,
orchids,

cf.

e.

g.,

Anemophilous.

Entophagous
Animals that feed inside of dead leaves and

roots, cf.

Ectophagous.

Entropy

The

degradation of energy, a measure of the degree of

disorder of a system.

Environment
The sum total

of

influence organisms,

all
cf.

the external conditions which

Habitat,

may

Site.

Environment, Fitness of

The
taining

suitability of

an environment or habitat for main-

life.

Environmental Clock

The

influence of environmental factors to initiate proc-

or activities of organisms, e. g., the initiation of flowerin

the cocklebur by the Photoperiodic influence of short
ing

esses

days and long nights.

126

Environmental Conditioning
See Conditioning, environmental.

Environmental Form
See Ecad.

Environment, Holocoenotic

The concept that the environmental factors act as a

whole or aggregate in their effect upon one or more organisms.

Environmental Resistance
The restriction caused by environmental
the increase in

numbers

factors

upon

of individuals in a population,

cf.

Biotic potential, Reproductive potential.

Enzyme
An organic

catalyst,

produced by living

determining a specific chemical reaction,

cells,

e. g.,

each kind

diastase

which

digests starch.

Eocene
The second

geological epoch in the Cenozoic Era, Tertiary period, began about 58 million years ago and lasted for
about 19 million years.

Eolian
See Aeolian.

Epeirogenesis
Great alterations in the level of the crust of the earth
such

as

the elevation or lowering of the surface of con-

tinents.

Epharmone
An organism
(q. v.).

which has been subjected

See ecad.

127

to

Epharmony

Epharmony
The acquirement by an organism
logical structures

by which

altered environment,

Epharmose
The process

cf.

it

is

of processes or morphoenabled to exist in an

Adaptation.

of gradual adaptation of a species to a

change of environment.

Ephemeral
Refers to short-lived existence.

Epibiotic

An

endemic surviving from a former

flora,

a Relic.

Epicole (Epibiont)
An organism living attached to another organism without benefit or harm to the latter, e. g., barnacles attached to
corals, algae on the bark of trees, cf. Commensalism, Epiphyte.

Epidemic

The

widespread occurrence in greater numbers than

is usually parasitic or
predatory.

usual of a species that

Epidermis

The

outermost layer of

of animals and plants; cork

cells replace the epidermis in stems and roots of older woody
cells

plants.

Epigeal
Refers to an organism that lives close to the ground, e. g.,
insects, cotyledons on seedlings such as the navy bean,

some
cf.

Hypogeal.

Epilid

A community of Epiphytes

(q. v.).

128

Epilimnion
The upper

layer of lakes, subject to disturbance

lying above the Thermocline,

(q. v.). cf.

by winds,
Hypolimnion.

Epinasty
The downward curvature
caused by

of a plant organ such as a leaf,

the greater growth on the upper surface than on

the lower.

Epiorganism

natural group or entity consisting of individual organisms, e. g., a society of termites, a stand or communitytype, syn. supraorganism.

Epiphyll
An Epiphyte

(q.

v.)

growing on a

leaf,

e.

g.,

certain

lichens.

Epiphyte

upon or attached to another plant, or

on
some
often,
non-living support, deriving no sustenance
from the supporting structure, e. g., Spanish moss on a live
plant growing

oak.

Epiphyton

An

faces

assemblage of organisms scattered on submerged sur-

which

later

may become

mechanically associated,

cf.

Periphyton, Lasion.

Epiphyfofic
An Epidemic

Epithalassa
The upper

disease in plants,

layer,

e. g.,

wheat

rust.

above the Thermocline, where Thermal

stratification occurs in the ocean.

Epizoan

non-parasitic animal living attached to another,

Commensalism.
129

cf.

Epizoochore

A Propagule

such as a spore or a seed that

is

carried

on

the body of an animal.

Epizootic
An Epidemic disease in animals,

Equilibrium,

The

cf.

Community

condition in which a community

only minor

Epiphytotic.

fluctuations in

its

maintained with
composition within a certain
is

period of tune.

Equilibrium, Ecologic
See Balance of nature,

Dynamic equilibrium.

Equivalence, Ecologic
See Ecological equivalence.

Eremean

(Eremic)

Refers to desert vegetation,

Eremophilous
Refers to organisms living in deserts.

Eremophyte

A plant growing in a desert.

Erg

The

part of the Sahara desert covered with sand dunes.

Ergot

and other grasses,

caused by the fungus Claviceps purpurea; in which darkdisease of cereals, especially rye,

colored structures replace the grain.

Ericaceous
Refers to the heath family of plants, Ericaceae.

Ericad

member

of the heath family, Ericaceae,

berry.

130

e. g.,

blue-

Ericilignosa

type of vegetation in which ericaceous plants are

inant or very abundant.

dom-

Erodible

A substance,
cf.

especially soil, that

is

susceptible to erosion,

Erosive.

Erosion

The detachment and movement

of particles of the land

or earth movements such as land-

surface
slides

by wind, water, ice,

and creep, cf. Accelerated

erosion,

Normal

erosion.

Sheet erosion.

Erosion Class

One

of several categories in a classification indicating the

degree of erosion.

Erosion

Pavement

layer of stones or gravel

after fine particles

on the

surface of the

ground

have been removed by erosion.

Erosive
Refers to the tendency of an agent such as water or wind
is preferred when referring to the

to cause erosion. Erosive

agent, Erodible

when

referring to the substance that

is

eroded.

Escape

plant found wild but which originated from a cultivated ancestor.

Escape Covert
Vegetation which is intended or used for protection by
animals from attack by enemies.

Escape Mechanism

structure, behaviour, or process that enables an organism to survive unfavorable conditions, e. g., shedding of
leaves,

burrowing, development of
131

cysts.

Escarpment

long, inland cliff or steep slope, usually high, formed

or possibly by faulting, syn. scarp.
erosion
by

Esker

A long, narrow ridge of gravel and sand deposited by a

stream flowing under or within a glacier, cf. Kame.
Esophagous (Oesophagous)
The portion of the alimentary

tract

between the pharynx

and the stomach.

Espinal

thorny woodland.

Essential Element
A chemical element required by green plants for normal
growth, such as the primary essential elements: hydrogen,
oxygen, nitrogen, phosphorus, and potassium; secondary
essential elements: sulfur, calcium, and magnesium; and the
trace or minor elements: iron, boron, manganese, copper,
zinc,

and molybdenum. The

last six,

and

traces of other

elements, are required in only minute quantities.

Establishment

The

successful

growth of an organism in a new location,

syn. Ecesis. cf. Invasion, Spread, Dispersal.

Estival
Refers to the

summer

season,

cf.

Aspection.

Estivation

The
mer and

condition in which an organism

in which

its

normal

or temporarily suspended,

Estuary
An arm

cf.

of the sea at the

may

pass the sum-

activities are greatly curtailed

Dormancy, Hibernation.

mouth

current of the river meets the tide.

132

of a river, in which the

Ethiopian Region

The faunal region in the realm Megagea (Arctogea); it

includes all of Africa except the northern corner and part of
southern Arabia.
Ethnobotany
The study of
people,

cf.

the use of plants by any race or group of

Paleobotany, Paleontology.

Ethnology
The study
divisions of

of the distribution

and

characteristics of the

mankind.

Ethology

The

comparative study of the Behaviour of animals.

Etiolation

The development
ing in the loss

abnormal

grown without light, resultof chlorophyll, a weak elongated stem, and

of a plant

leaves.

Etiology

The

study of the causes of diseases.

Eucoen
See Index species.

Eugenics

The study of the improvement of the genetic constitution of a population or species, especially the human race.
Eulittoral
The shoreward part of the Benthic zone in lakes and
oceans; the landward part of the littoral zone, including all
of the inter tidal region,

cf.

Littoral.

Euphotic Zone
The uppermost portion of

body of water which

re-

ceives sufficient light for Photosynthesis, cf. Aphotic, Disphotic, Photic zones.

133

Euplankton
Animal components

of the Plankton (q.

v.).

Euploid
Refers to the presence of a regular number of chromosomes, a multiple of the Haploid number, cf. Aneuploid.

Euroky
The capacity

of an organism to live under a wide range

of environmental conditions, syn. Eurytopic.

amplitude,

cf.

Ecological

steno-.

Eurytopic
See Euroky.

Euthenics

The

study dealing with the improvement of living conditions in order to secure better human beings, cf. Eugenics.

Eufrophic
Refers to bodies of water, accumulations of peat,

etc.,

which are rich in mineral nutrients and organic materials,

therefore productive. Oxygen may be deficient seasonally in
lakes or ponds,

cf.

Oligotrophic, Dystrophic.

Evaporative Power of the Air

The

environmental factor complex including factors such

as temperature, relative humidity,

and wind

that influence

the evaporation of water from organisms and from other

bodies containing water.

Evaporimeter

An

instrument to measure the Evaporative power of the

air such as an open pan of water or an Atmometer (q. v.).

Evapotranspiration
The sum total of water

lost

from the land by evaporation

and plant Transpiration.

134

Evapotranspirometer

A soil-filled container covered with living vegetation and

supplied with water to measure transpiration and evaporation.

Even-aged
Refers to a stand of trees in which only small differences
in age occur between the individuals; in young stands differences should not exceed 10 to 20 years, in mature stands
not more than 30 to 40 years, cf. Age-class.

Evolution

The

process of Natural or Artificial selection acting

genetic diversity in organisms.

upon

Evolution, Convergent
The development during the course of evolution of similar structures or habits in

lated taxonomically.

cf.

organisms that are not closely

re-

Taxonomy.

Exchange Capacity
See Cation-exchange capacity.

Exclosure

An

area fenced to exclude certain kinds of organisms,

Enclosure.

cf.

Exclusive Species

species belonging to the highest Fidelity class (BraunBlanquetj, one which occurs exclusively or almost so in "a
specific

kind of vegetation unit.

Exclusiveness

The degree in which a particular species is restricted to

a particular kind of community to the exclusion of other
communities, cf. Exclusive species, Fidelity.
Excretion

The

elimination of substances from the bodies of or-

ganisms.

135

Excurrent

A plant with one main stem, the lower branches longer

than the upper, e. g., a spruce tree.
Exempt Stock
Livestock such as work or saddle horses and milk cows

which are permitted

Public

Domain

to graze

on National

Forests or the

free of charge.

Exfoliation

The peeling off of material in thin layers from the surface of rocks or the flaking off of scales or other parts of
organisms.

Exoskeleton

A hard, supportive structure in the outer part of the body

of

many

kinds of animals,

e. g., shell

of a crab.

Exothermic
Refers to the release of heat.

Exotic
Refers to any organism that is not native in the area
it occurs; introduced, cf. Endemic, Indigenous.

where

Experimental Design
The plan of an experiment,

especially to insure that the

data to be secured will be suitable for

statistical analysis.

Exploitation

The
unused

ability of

an organism to

vital resources, cf.

find,

occupy, and retain

Competition, Interference.

Exsiccata
Dried, preserved specimens of plants.

Exsiccation

The process of promoting the development of desert conditions through human activity or climatic change, cf. Siccation.

136

Extracellular
Refers to something outside of a
a multicellular organism,

cf.

cell,

but may be within

Intracellular.

Extraclinal
Refers to an organism or a population that
of a Cline (q.

is

not part

v.).

Extraneous
Refers to the presence of an organism near the border
of its range or nearer the margins than the Center of dispersal.

Extrinsic Cycle
See Cycle.

Eyrie

The

nest or brood of a bird of prey such as an eagle or

raven.

137

Faciation

A
lacks

part of a Climax Association (sensu Clements) which

some of the dominants of the association because of

slight differences in

environmental conditions,

cf.

Lociation.

Facies
(1)

See Faciation.

(2)

The

general appearance or aspect

of a plant, population, or community, cf. Aspection. (3)

modification of the Bio tope, differing recurrently from the

variation in a comtypical conditions in minor ways. (4)

munity such as a dogwood or mountain laurel shrub facies
in

an oak

forest.

Facilitation, Social

The

effect of the

presence of one organism

upon

the

behaviour of another.

Factor, Ecological

Any

part of the environment that influences the

an organism,

cf.

life

of

Biotic, Limiting, Density-dependent factors.

Facultative
Refers to the capability of an organism to live under

138

various conditions such as parasitism and saprophytism.

cf.

Obligate parasite.

Fairy Ring

circle of mushrooms arising from underground mycelial

growth, usually accompanied by a luxuriant ring of vegeta-

tion, fairly

common

in grasslands.

Fall Line

line connecting the points where rivers leave the

uplands for the lowlands, marked by an increased slope and
waterfalls, e.g., the Atlantic coastal plain adjoining the Ap-

palachian Mountains.

Fallout

The dropping

to the earth from the air of solid material,

the
radioactive
dust from atomic explosions.
particularly

Fall Overturn
See Spring overturn.

Fallow
Refers to cropland left idle except for tillage in order to
destroy weeds and accumulate water and nutrients for use
of a crop to be planted later, cf. Summer fallow.

False Annual Ring

More than one of the Growth rings that may be produced
in

woody

plants in a single season.

Family
In the

classification of

organisms a group of one or more

related genera, e.g., the rose family in

berries, etc., are classified. In ecology

community comprising

which the roses, strawit has been used for a

individuals of a single species.

Fasciation

The

condition in plants in which stems and branches

have grown together to form a malformed and flattened
structure.

139

Fascicle
A dense cluster or bundle such as three to
in groups

on pine

five leaves

trees.

Fauna

A collective term to include all the kinds of animals in

an area or in a geological period.
Fauna! Region

An

area containing characteristic kinds of animals,

the Oriental Region, (q. v.).

e.g.,

Fecundity
Capability of an organism to produce reproductive units
such as eggs, sperms, or asexual structures, cf. Fertility.

Feed
Harvested forage including hay or fodder, or grain, grain
products,

and other

foodstuffs that are processed for feeding

livestock.

Feedback
The return

of a substance to a former condition or locasuch as the absorption of calcium by plants and the
return to the soil when the leaves fall to the ground and
tion,

decay.
Fell, Fell-field

tract of bare, elevated

country which

is

in

more or

uncultivated condition.

less

Felling
In selective felling only certain trees are cut

down

in a

forest, in clear felling all are taken.

Fen

A tract of low, marshy ground containing peat, relatively

rich in mineral

salts,

alkaline in reaction, situated in the

and around fresh-water

from Moors (q. v.).

upper parts of old estuaries

vegetationally distinct

140

lakes,

Feral
Refers to an organism that has escaped from cultivation
or domestication and become wild again.

Fermentation
The chemical

alteration of organic substances by organisms, especially yeast and bacteria, e.g., alcoholic fermentation
in which sugar is changed to alcohol and carbon dioxide by

the enzyme zymase, produced by yeast.

Fertile
Refers to the capability of an organism or organ such as
a stamen, pistil, or ovary to carry on reproductive functions.
Fertility
(1)

The

capability of an organism to produce living offFecundity. (2) The quality of a soil which enables

spring, cf.
it to provide substances in adequate amounts properly balanced and available for the growth of specified plants when

other environmental factors are favorable.

Fertilization

The union

of egg

and sperm, or of two Gametes

(q. v.).

Fertilizer
Any material added to soil to supply one or more plant
nutrients, usually not including lime or gypsum.

Fibrous Root System

The aggregate of the numerous, similar roots arising from

the base of the stem such as occurs in corn and the grasses.
cf.

Tap

root system.

Fidelity
The degree of regularity or "faithfulness" that a species
occurs in certain plant communities, expressed in a 5-part
scale: (5) Exclusive, (4) Selective, (3) Preferential, (2)

panion, indifferent, (1) Accidental, strangers

141

(q. v.).

Com-

Field

Border Plantings

Vegetation established on the borders of fields to conserve

soil and to provide cover and food for wildlife, e.g., a
strip
of multiflora rose.

Field Capacity
The moisture content of a

soil, expressed as the perof

centage
oven-dry weight (100-110 C.) after the Gravitational water has drained away; the field moisture content

two or three days

after a soaking rain. cf. Capillary water,

Water-holding capacity.

Field

Crops

Crops such

as grain, hay, root,

vegetable (truck) and fruit crops.

and

fiber in contrast to

Field

Layer
The stratum

of vegetation formed

by

grasses, forbs,

and

dwarf shrubs.
Field Strip Cropping
The kind of Strip cropping in which crops are grown
in parallel strips across a slope but which do not follow
contour lines, and strips of grass or other close-growing plants
are

grown

alternately with the strips of cultivated crops.

Field Test

An
tions,

experiment conducted under ordinary field condiusually less subject to control than a precise experi-

ment.

Filament

The
Filter

stalk of

an Anther or of a down-feather.

Bridge

A land connection,

temporary in duration and restricted

in extent, limiting the kinds of organisms which can migrate

over it, e.g., the Bering Strait in the Pleistocene, cf Corridor,
.

Sweepstakes bridge.

Filter Strip
strip of permanent vegetation sufficiently wide and
dense above a farm pond, diversion terrace, etc., so it will

and cause deposition, thus preventing silting

in the water or structure below.
retard run-off

Fine-textured Soil

A soil

that consists mainly of

silt

and

clay.

Fiord (Fjord)

narrow, often long and deep inlet of the sea as in the

coasts of

Norway and

Alaska, very likely formed

by

glaciers.

Firebreak

A strip of land from which inflammable materials have

been removed in order to check or stop a creeping or
running

fire.

Fire Control Line

The
of a

fire

line along

which

efforts are

made

to stop the

advance

or from which to start to backfire.

Hazard
The risk of

Fire

of the

probabilities that a fire may start because

inflammability of materials under the prevailing

climatic conditions.

Firn
See N4v4.

Bottom
The Flood plain

First

is most immediate to a stream, or

above a stream, consequently some

that

at the lowest elevation

are frequently flooded.

Firth

long,

narrow arm of the sea or lower portion of an

estuary, especially in Scotland.

143

Fishway

fish to

sloping structure over which water flows, to enable

ascend a stream around a dam or other obstruction;

a fish ladder.

Fission
(1)

Reproduction of a unicellular organism by simple

bombs in which

division into two parts. (2) Refers to atomic

elements such as uranium and plutonium are

products

as,

for example, Sr 90 , I 131 ,

split

into

and Cs 157 which are

,

formed during the explosion.

Fitness

The
that

degree of Adaptedness

an organism

Fitness of the

The

(q. v.) to

the environment

possesses.

Environment

environmental conditions such as the

nature of the water, gaseous composition of the atmosphere,
and temperatures for the maintenance of life or for the
suitability of

activities of a certain

Fixation

organism.

(in Soil)

The

conversion of a soluble substance such as phosfrom

a soluble or exchangeable form to a relatively
phorus
insoluble form.

Fjaeld (Fjeld)

A more or less barren upland area (Scandinavia). See Fell.

Flachmoor
A moor with
soil

poor in

salts

Flatworm
A member

or even slightly concave surface and

and acid in reaction.
a

flat

of the

phylum Platyhelminthes,

tapeworms.
144

e.g., flukes,

Layer

(Soil)

Sometimes used to designate the

litter which can still be recognized
cf.

horizon,

layer,

partially decomposed
as to origin and age.

layer.

Flocculation

The

aggregation of suspended colloidal material or very

fine particles into larger masses or floccules.

Flood Plain

The nearly level land forming the bottom of a valley

in which a stream is present and usually subject to flooding,
cf.

First flood plain.

Floodway

channel usually bordered

of carrying flood water.

by

levees for the purpose

Flora

The sum
time.

cf.

kinds of plants in an area at one

Vegetation, Fauna.
total of the

Floral Region
See Floristic region.

Floret

The

small flower of grasses or Composites.

Florigen

hormone evidently made in the leaves which after

translocation to apical Meristem initiates the formation of
flowers.

Floristic Area
An area in which a certain degree of homogeneity exists
because of similarities in the areas occupied by various
species.

145

Florlsttc Composition
The kinds of plant species, in the aggregate, that occur
in a community or in an area.
Floristic

Element

Species that are characteristic of a certain territory but

occur also in a different one, e.g., an arctic species growing
in the high Rocky Mountains is an arctic element in the
flora of the Rockies.

Floristic

Region

A portion of the earth's surface supporting a characteristic

flora

which developed largely within this portion, e.g., the

North American Region of the Boreal Kingdom.

Atlantic

Floristic Territory
geographic area characterized by the common occurrence of a number of species which are more or less confined

to

it,

but other species may also be present.

Flower
The organ

of the class Angiospermae, flowering plants,

consisting of one or more pistils (carpels) or stamens, or both,
and usually a calyx (composed of sepals) and a corolla (com-

posed of

petals).

Flower Induction
The stimulation, presumably by
initiates the

Florigen

(q. v.)

which

production of flowers.

Fluctuation

relatively irregular departure

average conditions,

cf.

Community

from more normal or

dynamics.

Fluke

parasitic flatworm in the class Trematoda,

Platyhelminthes, e.g., the liverfluke in sheep.

phylum

Flume

An

open conduit of wood or other material

146

for carrying

water or other liquids across a creek, ravine, or other depression which lies across the course of a canal or ditch location.

Flyway

migration route of birds,

e.g.,

the Mississippi River

flyway.

Fodder
The dried, cured
ghum,
cf.

plants of crops such as corn and sorincluding all parts above ground including the grain,

Stover,

Hay.

Foehn

A dry wind which

is

warm

for the season. It blows

down

leeward slopes of mountains, especially in the Alps.

cf.

Chinook.

fog
The
smoke

condensation of water vapor on particles of dust or

particles.

Foliaceous
Refers to structures that are leafy or

leaf-like, thin.

Foliage Cover
See Cover.

Foliar Diagnosis
Evaluation of the status of plant nutrients in a plant,
or the plant-nutrient requirements of a soil, by the analysis
of leaves.

Follicle

many-seeded fruit developed from a simple ovary

which when ripe splits along a single line, e.g., the larkspur
dry,

fruit.

Food-chain

figure of speech for the

dependence for food of organ-

147

beginning with plants or

scavenging organisms and ending with the largest carnivores.
isms

upon

others

in a series,

Food-cycle
All the interconnecting Food-chains in a community,
syn. food-web.

Food-niche

The

particular location of an organism in a Food-cycle.

Food-pyramid

graphic representation of the food chain which indinumbers of producer organisms at the base

cates the large

and the progressively decreasing numbers

of herbivores

and

carnivores above.

Food-web
See Food-cycle.

Forage
Unharvested plant material available as food for domestic
animals, may be cut for hay or grazed; after cutting it is
called Feed. cf. Fodder.

Forage-acre

theoretical concept, the quantity of forage

of land which

is

pletely utilized

on an

acre

completely covered with herbage and com-

under proper management.

Forage-acre Requirement
The number of forage acres needed

for the

maintenance

of a mature grazing animal for a certain period of time.

Forage Fish
Small kinds of

used

as

fish

which reproduce

prey by predatory

prolifically

and are

fishes.

Forage Ratio
This

is

the ratio of the percentage of a certain prey

148

organism present in the food of a predator divided by the

percentage of this prey that is present in the habitat.

Forage Volume
(1) The parts

of a plant within reach of animals for

measure of the yield of Forage, the

grazing. (2)
of
amount
forage produced on a range area during a

total

year.

Forb

An

herbaceous plant that is not a grass nor grasslike such

as a sedge, e.g., sunflower, geranium.

Foredune

low dune, often occupied by a sand-binding

grass,

bordering the sandy shore of a sea or lake.

Foreshore

The

portion of the shore occupied daily by

tides.

Forest

stand of trees growing close together with associated

plants of various kinds.

Forest Cover

The living plants and dead organic material occupying

the surface of a forest, often restricted to the woody plants
covering the ground,

cf.

Basal cover.

Forest Edge

The border, or Ecotone, of a forest with another kind

of vegetation such as grassland.
Forest Floor

The deposits of plant material

on the ground in a

such as leaves and branches

forest.

Forest Influences
All the effects or Reactions of a forest

upon

the habitat

or the environmental conditions, e.g., aiding in maintenance

of uniform stream flow, shading the ground.

149

Forest

Type

forest stand that

is

essentially similar

throughout

its

extent in composition under generally similar environmental

conditions. It includes temporary, permanent, climax, and

cover types.

Form

A botanical
characteristics

taxonomic category based upon more

and with a

less distinct

trivial

geographical range

than those of the Subspecies or Variety.

Formation
One of the

largest subdivisions of the vegetation of the

of
earth, usually
great geographical extent, composed of communities that are similar in physiognomy and broad environ-

mental relations,
America,

cf.

the deciduous
Biome.
Climax,
e.g.,

forest of eastern

North

Formenkreis

series of related

forms distinguished geographically

and which originated entirely or primarily by geographic

isolation.

Fossorial
Refers to animals that burrow in the
cf.

soil, e.g.,

the mole,

Ambulatorial.

(of a Community)
stand so small that it lacks the species composition
and other characteristics of the Community.

Fragment

Fragmented Structure

(Soil)

A soil composed largely of particles that have well defined

faces

and

edges,

cf.

Granular structure.

Free-martin

sexually imperfect female

a twin of a male animal.

150

calf, sterile usually,

born

as

Frequence
See Frequency.

Frequency
The degree

of uniformity with which individuals of a

and more specifically in

species are distributed in an area,

a Stand, cf. Constancy.

Frequency Class
One of the small groups

which the Frequency indices

in a stand may be classified.

of the various species

into

Frequency Index
The quantitative

expression in percentage of Frequency,

a
species occurring in 15 of 20 sample areas in a stand
e.g.,
has a frequency index of 75 per cent.

Law of

Frequency,

The

generalization which states that when Frequency

indices of species in a stand are classified into five main

a double peak occurs in homogeneous vegetation,

classes

i.e.

Zone

Frigid

The

portions of the earth north of the Arctic Circle and

south of the Antarctic Circle. Cf. Temperate zone. Tropics.

Frigorideserta

Tundra or cold

arctic

and

alpine,

open communities.

Fringing Forest

strip or

zone of forest along a stream bed.

cf.

Gallery

forest.

Front

The border

of cold

and warm

air masses at the earth's

surface.

Frost
(1)

The

act or state of freezing, or injury to organisms

151

because of low temperatures, especially near the beginning

or the end of the growing season. (2) Particles of frozen water
or

dew

on the

(hoarfrost) appearing

earth's surface at 32 F.

or lower.

Frostless

The
first

Season

period between the

last frost in

the spring

and the

one in the autumn.

Frost Resistance

The

capability of plants to survive the formation of ice

in
their tissues.
crystals

Fruit

The ripe ovary or group of ovaries with any other

may be regularly associated with it, e.g., a grain of

that

parts

corn,

a gooseberry fruit, an apple pome.

Frutescent
Resembling a shrub somewhat. See

Fruticose.

Fruticeta
Vegetation types consisting of scrub

forests.

Fruticose
Shrubby,

cf.

Suffruticose.

Fruticose Lichen
A Lichen with a Thallus ten cm. or more
Cladonia rangiferina, the reindeer "moss."

Fucoid
Resembling a seaweed,

tall,

e.g.,

especially Fucus.

Fugacious
Refers to a structure that
plant,

e.g.,

falls

or separates early from a

sepals or petals of some flowers.

Fully Stocked
Refers to a stand which contains as
152

many

trees or as

much

material of the species and of the age as the Site can support.
Cf. Overstocked, Understocked.

Fumarole

A hole in the earth from which gases such as CO 2 and

steam escape under pressure, as seen in the Valley of Ten
Thousand Smokes, Alaska.
Fungicide

substance that

is

toxic to fungi, e.g. Paris green.

Fungivorous
Refers to organisms which consume fungi,

e.g.,

some

Collembolons and mites.

Fungoid
Resembling a fungus.

Fungus
One of

the true fungi, belonging to the

phylum Eumyco-

phyta; plants lacking Chlorophyll such as the molds, yeasts,

mildews, rusts, and mushrooms. They may be either Parasitic

or Saprophytic.

Funiculus

The
Furrow

stalk of the

Ovary in

plants.

Dam

small earth

within a furrow,

dam

cf.

for the purpose of holding water

Lister.

Fynbos
Sclerophyllous vegetation on plateaus and mountains in
South Africa, ecologically equivalent or similar to Macchia of
the Mediterranean region and the Chaparral of California.

153

Gallery Forest (Galleria)

Woods

or a narrow zone of forest along a stream in grass-

land, savanna, or other

open vegetation.

Game Management
The

practice of producing sustained annual crops of wild

game on land.

Game

cf.

Range management.

Refuge

An

Enclosure for the purpose of controlling or prohibitthe

ing
hunting, fishing, or otherwise destroying game animals, birds, fish, and other animals.

Gamete

cell, a sperm or egg; in some of the simplest

the
organisms
gametes are not differentiated into egg and

sex

sperm.

Gametocide

An

Herbicide that prevents development of or destroys

Gametes.

Gametophyte
The plant or

generation in organisms that produces

contains
the
Haploid number of Chromosomes.
gametes,

154

Gamma Radiation
One kind

of ionizing radiation, electromagnetic, readily

penetrates biological materials.

Gamopetalous
Refers to flowers that have

more or

less

united Petals.

more or

less

united Sepals.

Gamosepalous
Refers to flowers that have

Garique (Garrique)
Open vegetation consisting

of dwarf, evergreen Scrub

poor land in the Mediterranean region,

cf.

on

Maquis.

Gastropod

An

animal in the

class

Gastropoda, phylum Mollusca,

e.g., slug, snail.

Cause's Principle

The

generalization that states that two species do not

occupy exactly the same Niche. See Competitive exclusion
principle, GrinnelVs axiom.

Geiger Counter

An

instrument for detecting Ionizing radiation.

Geitonogamy
The Pollination of a flower by pollen from another flower
on the same

plant, cf.

Gemma
A structure

Autogamy, Cleistogamous^ Xenogamy.

consisting of a few cells which becomes

the parent and grows into a new plant, found

separated from
in certain liverworts.

Gene

localized unit of genetic material with a specific function in transmitting characters from one generation to the
following one.

155

Genecology
The study

of population genetics in relation to the

habitat conditions; the study of species and other taxa by the
combined methods and concepts of ecology and genetics.

Gene Flow
The

duplication and dispersal of genes in a population.

Gene Pool
In a narrow sense, the genie material of a local interbreeding population at the present time. In a broad sense,
the total genie resources or materials of a species throughout
its

geographical range.

Generic
Refers to Genus.

Generic Coefficient
The ratio of the number

of genera to the

number

of

species in an area.

Genetic Drift
Accidental fluctuations in the proportions of a particular
do not occur, which

Allele so that exact Mendelian ratios

result in the fixation or loss of certain genes in small

populations without reference to selective value, cf. Natural

may

selection.

Genetics

The branch

of biology dealing with Heredity in all

its

phases.

Genome (Genom)
The
or

set of different

Haploid nucleus;

Chromosomes,
the

Diplod

as

found in a Gamete,
contains two

nucleus

genomes, Polyploids more than two.

Genotype
The entire genetic constitution,

or the

sum

of an organism, in contrast to the Phenotype.

156

total of genes,

Genus

species, or occasionally only one

in the classification of organisms, e.g., the white

group of related

species,

used

and Scotch pines belonging

to the genus Pinus.

Geobiont

An

organism that spends all its life in the

and nematodes.

soil,

e.g.,

certain fungi, protozoa,

Geochronology
The study of

biological

and meteorological events

in

relation to time.

Geocline

gradation or Cline

(q. v.)

based on topographic or

spatial separation, cf. Ecocline.

Geocole

An
e.g.,

organism that spends a portion of

certain

mammals,

reptiles,

its life

in the soil,

and other animals,

cf.

Geo-

biont, Geoxene.

Geoecotype
See Geotype.

Geographic Race

A Race restricted to a certain geographic area. cf. Ecotype.

Geological Erosion
See Normal erosion.

Geomorphology
The branch of physical geography that deals with the
form and arrangement of the earth's crust.
Geophile
See Geocole.

Geophyte
One of Raunkiaer's Life-form classes of plants in which
the buds or other Perennating parts surviving unfavorable
157

seasons are buried in the surface

soil, e.g.,

plants with bulbs,

tubers, or rhizomes.

Geosere

series

of Climax Formations throughout geological

time in an area.

Geotaxis

Taxis

(q. v.) in

Geotome
An instrument

response to gravity.

for securing soil samples.

Geotropism

in response to gravity, e.g., the main

roots of plants growing downward, the main stems upward.

Tropism

(q.v.)

Geotype

genotypic population occurring in a habitat which is

partly isolated by topographic barriers; includes most geographical

Races

and

Subspecies.

Syn.

geoecotype.

cf.

Genotype.

Geoxene
An organism

that occurs accidentally in the soil.

cf.

Geocole.

Germination
The process

of growth renewal of a seed or spore; a seed

considered to have completed germination in some instances when the Hypocotyl projects outside of the seed coat,

is

in other instances

when

the seedling appears above ground.

Germ Plasm
The protoplasm which transmits the hereditary characters
or Genes (q. v.).
Gestation Period

The period of time that the

uterus of an animal.
158

embryo and

fetus are in the

Horizon

A soil layer developed wholly or partly in Gley (q. v.) soil,

characterized by the presence of ferrous iron and usually by
neutral gray colors.

Gigantism (Giantism)

plant showing excessive vegetative growth.

Gilgai

The

type of microrelief characterized by a succession of

micro-basins and micro-knolls or many small ridges in nearly
level areas on clay soil having high coefficients of expansion
and contraction with changes in moisture content; "pits-

and-mounds."

Girdling

The removal

of a ring of bark or tissues from a stem,

the
death
of the plant.
causing

Glacial Drift
See Drift.

Glaciation

The covering of an area by a glacier or by an ice-sheet,

or the geological action of the glacial ice upon the land.
Gleization

The

Gley

soil-forming process in which Gley soil

is

formed.

(Glei) Soil

formed under the influence of water-logging and

lack of oxygen; usually neutral gray in color and containing
soil

reddish

brown

deposits of ferrous hydroxide,

cf.

horizon.

Gloger's Rule

The generalization which states that animals in warm

climates tend to be darker in color than those in arid or cool
regions.

159

Glycophyte

is low in
American elm.

plant growing in soil that

contrast to Halophyte,

e.g.,

salt content, in

Graded Terrace

terrace having a continuous slope along

Level

its

length,

cf.

terrace.

Grain

An
is

Indehiscent fruit in which the coat of the single seed

e.g., wheat.

united with the ovary wall,

Gramineous
Refers to the grass family, Gramineae.

Graminivorous
Refers to an animal that eats grass.

Graminoid
Refers to an herb with long, narrow leaves.

Granular Structure (Soil)

A soil made up chiefly of particles
rather indistinct faces and edges,

cf.

or aggregates that have

Fragmented

structure.

Grass

plant in the family Gramineae with characteristically

florets, grain type of fruit, and with narrow, usually elongated leaves which are attached in two
ranks to the jointed stem or culm.

reduced flowers of

Grassed Waterway

natural or artificially made course for the flow of

water, usually shallow, on which erosion-resistant grasses are
grown, to permit water to run off fields thus reducing
erosion where the crops are growing.

Grassland
cf.

Vegetation consisting chiefly of grasses or grasslike plants,

Steppe, Prairie, Pampas, Meadow, Veld, Savanna.
160

Grasslike Plant
A plant which resembles

a true grass,

Gravitational Water
Water in large pores in the
the force of gravity

major

soil

sedges, rushes.

which drains away under

when underdrainage

Gray-Brown Podzolic

soil

e.g.,

is

free.

Soil

group having a thin organic and thin

organic-mineral layers over a grayish brown leached layer

which rests upon a brown B horizon richer in clay than the

horizon above; formed under deciduous forests in a moist

temperate climate.

Grazing
The feeding by

livestock

and game animals on

live or

standing plants other than Browse.

Grazing Capacity
The maximum number

of animals or animal units per

acre, or acres per animal, that a grazing area can support
without deterioration, cf. Carrying capacity.

District
administrative unit of the Federal rangeland established by the Secretary of the Interior under provisions of

Grazing

An

the Taylor Grazing Act of 1934, as amended; or an administrative unit of a state, private, or other range lands, established

under

state laws.

Grazing Land
Land used regularly

for grazing; not necessarily restricted

to land suitable only for grazing but cropland and pasture
used in connection with a system of farm crop rotation are

usually not included,

cf.

Range.

Grazing Permit

An

authorization for the grazing on public or other lands

161

under specified conditions, issued to a livestock operator by

the agency in charge of the lands.

Grazing Preference
The criteria used in

the administration of public grazing

lands for the issuance of grazing permits and licenses.

Grazing Unit

division of the

Range

for the facilitation of adminis-

tration or the handling of livestock.

Green Manure Crop

it is

the

crop grown for the purpose of turning under while

still green, or shortly after maturity, in order to improve

soil.

Gregariousness

The
e.g.,

tendency of organisms to congregate or form groups,

reindeer, cattails. See Sociability.

Grinnell's

Axiom

The generalization

stating that no two species in the same

can
general territory
occupy for a long time the same
Niche,
cf.
Cause's
ecologic
principle.

Ground Cover
See Cover.

Ground Water
Water standing
lying strata,
springs and

in or

moving through the

soil

and under-

Gravitational water, the source of water in

wells, cf. Runoff.

Group Control
The

control or influence of the behaviour of a group of

animals, by means of the cue behaviour or a signal of specific
animals.

Growing Point
One

of the sections of a plant body in which growth

localized, especially the tips of stems and roots.

162

is

Growing Stock
The total number

or total volume of

all

the trees in an

area.

Growth Form
The

characteristic shape or appearance of an organism

development in response to the impinging

as a result of its

environmental conditions within its genetic constitution,

Habitat form, Phenotype, Genotype.

cf.

Growth Layer

layer of Xylem and Phloem produced in woody stems

usually during each growing season, cf. Annual ring.

Growth Ring

A Growth

layer seen in the cross section of a

woody

stem.

Growth Substance
Any

chemical produced by a plant, or synthetically, that

regulates plant growth,

cf.

Hormone.

Gully

A channel or small valley formed by running water which

usually flows only during and immediately after heavy rains

or the melting of snow; it may be branched or linear and
fairly long, narrow, and uniform in width; smaller than a
ravine, deeper than a rill.

Gully Erosion
Removal of stones,

gravel,

and

finer material

by running

water with the formation of channels that cannot be smoothed

out completely by ordinary cultivation.

Guttation

The

exudation of water in liquid form from plants

through HydathodeSj (q. v.). cf. Transpiration.

Gymnosperm

plant in the class Gymnospermae of the seed plants,

Spermatophytes, in which the seeds are not enclosed within

an ovary,

e.g.,

pine, spruce,

cf.

163

Angiosperm.

Gynandromorph
An organism containing
istics, e.g.,

certain insects,

both male and female character-

cf.

Hermaphrodite.

Gynandrous
Refers to plants in which the stamens are fused with the
pistil, e.g.,

certain orchids.

Gynoecium (Gynaecium)
The

Carpels or Pistils of a flower considered collectively.

Gypsophilous
Refers to plants growing characteristically on
in

gypsum.

Gyttio

The

jelly-like

ooze on lake bottoms.

164

soils rich

Habit

The general appearance of a plant such as

or decumbent and trailing, cf. Life-form.
Habitat
The sum
place that

is

community,

tall

and

erect

environmental conditions of a specific

occupied by an organism, by a population, or a
total of

cf.

Environment, Niche,

Site,

Microhabitat,

Standort, Station.

Habitat Form
The Growth form or appearance
is

of an organism which

characteristic of a certain Habitat, cf.

Epharmony,

Life-

form, Eco type.

Habituation

The relatively waning response of an organism resulting

from repeated stimulation which is not followed by any
reinforcement.

Hadal Zone
The very deep
cf.

part of the ocean, below 6000 meters,

Abyssal.

165

Holorcn
Refers to saline conditions present in the
beginning of a Halosere (q. v.).

soil

at the

Half-shrub

A
base,

perennial plant that

and partly herbaceous,

is

partly woody, usually at the

e.g.,

Artemisia frigida.

Halic
Refers to saline

soil

or to plants growing in such

soil.

Halicole

plant growing in soil with a high content of

salts.

Halobiont

Any organism

that grows in a Saline habitat.

Halomorphic
Refers to a soil found in poorly drained depressions in
and semi-arid regions, cf. Hydromorphic, Solonchalk,

arid

Solonetz.

Halophyte

A plant growing in Saline soil.

Halosere

The

series of stages in Succession originating

area. cf. Sere, Hydrosere, Xerosere, Halarch.

on a Saline

Hammada (Hamada)
of

Rocky uplands in deserts, bare of fine soil or sand because

wind action, used especially in the Sahara.

Hammock
A mesic

area occupied by a community of hardwoods

or
an
island in a swamp (Okefinokee swamp).
(Florida)

Haplodiploidy

The

condition occurring in some Arthropods in which

males develop from unfertilized eggs and females from
fertilized eggs.

166

Haploid
Refers to an organism or part of one in which the nuclei
contain a single set of Chromosomes, i.e., one Genome (q. v.),
e.g.,

Spores, Gametes, Gametophytes, certain male animals

such as bees.

cf.

Hardening
The increase

Diploid, Tetraploid, Polyploid.

in resistance to frost in a plant tissue.

Hardiness

The

capability of plant tissue to survive the formation of

ice crystals within them. cf. Frost resistance.

Hardpan

A cemented, hardened layer in the soil, cemented by iron

oxide,

silica,

organic matter, or some other substance,

cf.

Claypan.

Hard Seed
The condition

of

some

seeds in

which water absorption

and germination do not occur although the environmental

e.g., seeds of many legumes and

conditions are favorable,

trees.

Hardwood
The wood

of a tree in the Angiosperms (q.

oak, in contrast to Softwood (q. v.).

v.), e.g.,

the

Haustorium

specialized organ of certain parasitic plants

which

penetrates the Host and absorbs food from its tissues, e.g.,
special hyphal branch, a specialized structure in dodder.

Hay
The

dried,

mowed

stems and leaves, often including also

and seeds, of grasses and forage legumes
and clovers, cf. Fodder, Stover.

flowers or fruits

such as alfalfa

Headquarters
The main center

or centers of activity of an animal,

167

e.g.,

the larvae of the longicorn beetle in dying or dead wood,

cf. Habitat, Niche.

Heat Budget
The amount

of heat expressed in

gram calories that is

body of water from

necessary to raise the temperature of a

the winter to summer temperatures.

Heath

community usually occurring in cool climates, often

without trees and uncultivated, characterized by
usually
dry,
low shrubby plants mostly in the family Ericaceae, cf. Moor,
Bog, Marsh, Swamp.

Heaving
The partial
from

raising of plants out of the ground resulting

the freezing and thawing of the soil during the winter,

often breaking the roots.

Hedgerow

A strip

of shrubs or small trees, often planted, enclosing

a field or other area.

Heel-in
Placing young plants such as fruit trees in a temporary
trench with soil over the roots to protect them from drying
until they are permanently planted.

Hekistotherm

plant growing in a cold region, which requires less

heat than other kinds of plants, growing where the average

temperature for the warmest month of the year is less than

50 F., e.g., mosses, lichens, sedges, etc., in the Arctic, cf.
Megatherm, Mesotherm, Microtherm.

Heliophyllous
Refers to organisms that grow best in full sunlight.

Heliophyte

A Heliophyllous organism.
168

Heliophobous
Refers to organisms which grow best in the shade. Syn.
Sciophyllous, Shade plant.

Heliotropic
See Phototropic.

Helminth

worm, usually

parasitic.

Helophyte
One of Raunkiaer's
plants whose
e.g.,

Life-form classes, consisting of marsh

Perennating parts are in the soil under water,

arrow-head,

cf.

Geophyte, Hydrophyte.

Helotism

term that has been used for the interaction of two

organisms such as an alga and fungus in a lichen. See Mutualism, Parasitism, Symbiosis.

Hematypic
Refers to reef-building corals which contain zooxanthellae

and

algal Symbionts.

Hemerocology
The ecology of
gardens, parks,

land that

fields, cf.

is

modified by

man

such as

Culture community.

Hemerophyte

plant introduced into an area by man.

community, Exotic, RuderaL

cf.

Culture

Hemicryptophyte
One of Raunkiaer's

Life-form classes in which the buds

or Perennating parts of plants surviving unfavorable periods
are located at the soil surface,

cf.

Cryptophyte, Geophyte,

Chamaephyte.

Hemiepiphyte

plant that

is

Epiphytic

(q. v.) for

time.

169

only part of

its life-

Hemiparaslte

An

organism which

and a

(q. v.)

is

intermediate between an Epiphyte

Parasite (q.

v.).

Hemisaprophyte

plant which

is

intermediate between a Saprophyte

and an Autotrophic

(q. v.)

(q. v.)

organism.

Hepatic
Refers to the liver or to a Liverwort,

(q. v.).

Herb

plant with one or more stems that die back to the

ground each year; grasses and Forbs (q. v.) as distinct from

shrubs and

trees.

Herbaceous
Refers to plants with characteristics of an herb.

Herbage
Herbs

in a collective sense,

and any other plant material

used as forage by animals, especially Pasturage.

Herbarium

collection of preserved, classified plants.

Herbicide

chemical substance used for killing plants particularly

weeds, e.g., 2,4-D. cf. Insecticide.

Herbivore

An

organism that eats plants,

e.g.,

rabbit, sheep.

Herbivorous
Refers to a herbivore.

Herbosa
Vegetation consisting of non-woody plants.
170

Herd

group of animals, especially

cattle

or big game.

cf.

Band.

Herding, Close
Handling a band of sheep or goats in a compact group
and restricting the spread of the animals while grazing.

Herding,

Open

Handling a band of sheep or goats so the individuals

are allowed to spread freely while grazing.

Heredity

The

transmission of characters or directions from parents

to offspring, or the sum total of such characters.

Hermaphrodite

A plant with stamens and pistil in the same flower or an

animal that produces both male and female Gametes, e.g.,
the rose, earthworm, cf. Dioecious, Gynandromorph.
Herpesian
Refers to reptiles or amphibians.

Herpetology
The branch

of

zoology

concerning

reptiles

and

amphibians.

Heteroecious
Refers to organisms having stages of
different hosts, e.g.,

its

life-cycle

on

wheat rust which attacks wheat and the

barberry.

Heterogamy
cf.

The

production of unlike Gametes (egg and sperm),

Isogamy. (2) Alternation of generations (q. v.).
(1)

Heterogenesis
See Alternation of generations.
171

Heteromorphic
Refers to Alternation of generations
forms in different stages are unlike.

(q.

v.)

in

which

Heterophagous
Refers to animals which eat several kinds of food.

cf.

Omnivorous.

Heterophyte

Saprophyte or Parasite
Autotrophic, Holophytic.

(q.

v.).

See Heterotrophic,

Heteroploid
Refers to a population comprising Aneuploid, Diploid,

and Euploid members.

Heterosis

The
from

increase in vigor or the growth of offspring resulting

the crossing of genetically different parents, syn. Hy-

brid vigor.

Heterotrophic
Refers to an organism in which complex materials, especially organic foods, are the chief source of nutrition, in contrast to

(q. v.) organisms, e.g., animals, Parasites,

Holozoic, Mixotrophic.

Autotrophic

Saprophytes,

cf.

Heterotropous
Refers to an animal which

may wander into a coman

or
and
important
munity
play
unimportant part while
if
dies
it
does
not move into a more
but
eventually
present,
favorable environment, cf. Index species, Tychocoen.

Heterozygous
Refers to an organism that originated from the fusion of
gametes containing unlike Genomes (q. v.). cf. Homozygous.

Hibernaculum
(1) The habitat Niche where certain animals
(2) An overwintering bud of an aquatic plant.
172

overwinter.

Hibernal
Refers to winter, especially the winter season in contrast
to the Vernal, Estival, and other seasons, cf. Aspection.

Hibernation

of

state

Dormancy

especially

during

winter,

cf.

Estivation.

Hiemal
See Hibernal.

Hiemilignosa
Monsoon forest which merges

into savanna or park land

in a tropical-continental climate; woody plants lose their

small xerophytic leaves during the hot and dry summers.

Hierarchy

social rank-order of

animals formed through passive

submission, direct combat, or threat.

High Grass

A class of grasses,

virgatum.

cf.

6 to 8 feet high or more,

Medium-height

grass,

e.g.,

Panicum

Short grass.

Histology

The

of biology that deals with microscopic

structures or tissues of organisms.
division

H Layer

layer of completely decomposed litter, unrecognizable

on the surface of the mineral soil. See A horizon,

as to origin,

layer,

Hoar

layer.

Frost

A deposit of ice crystals formed directly from water vapor

in the air.

cf.

Rime.

Hochmoor

moor

that rises

from the edge towards the middle, so

173

that the

upper surface
growth of Sphagnum.

is

convex in

section, caused

by the

Hogback

A ridge with a narrow summit and steep slopes.

Hohenheim System

system of grazing followed by resting small pastures

or paddocks for short periods in rotation.

Holarctlc
Refers to the combined Palearctic
(q. v.) regions of the faunal realm

(q. v.)

and Nearctic

Megagea (Arctogea)

(q. v.).

Holard

A term used occasionally to designate

tent of the

the total water con-

soil.

Holism

The doctrine that life hi all its forms and the inorganic
environment form an interacting, integrated system, cf.
Ecosystem.

Holocoen
Equivalent to Ecosystem

(q. v.).

Holocoenotic
Refers to the joint action and interaction of a
of environmental factors

numbei

upon organisms.

Holoparasite

An

organism that

is

wholly

parasitic, e.g.,

wheat

rust.

Holophytic
Refers to an organism that utilizes light as the primary
source of energy, e.g., green plants, purple bacteria, cf. Autotrophic, Chemotrophic, Heterotrophic, Holozoic.

Holoplankton

An

organism that is in the Plankton (q. v.) during

entire life-cycle, e.g., Copepod. cf. Meroplankton.
174

its

Holozoic
Refers to a heterotrophic animal that ingests solid food,
digesting

it

internally.

Homeostasis
The maintenance

of constancy or a high degree of uni-

formity in functions of an organism or interactions of individuals in a population or community under changing

conditions, because of the capabilities of organisms to make
adjustments. Perceptual homeostasis is the state of maximum
predictability

organism,

cf.

and control of environmental stimuli by an

Steady

state, Stabilization.

Homeotherm
See Homoiotherm.

Home Range
The

area around an animal's established

traversed in

its

normal

Homesite
The location

home which

is

activities, cf. Territory.

of the nest or resting place that

is

in

regular use by an animal.

Homing
The

reaction of an animal to return to a given place

after displacement, e.g.,

homing

pigeons.

Homogeneity
Refers to the regularity in the distribution and abundance of the species in a community or area. cf. Frequency,

Homoteneity.

Homoiotherm
An animal which

is able to maintain the

temperature
an
body
approximate constant level independent
of the surrounding medium, "warm-blooded," e.g., birds,

of the

mammals,

at

cf.

Poikilo therm.

175

Homologous
Refers to structures of organisms that possess the same
phylogenetic origin, e.g., wings of bats and forelimbs of
a rabbit.

Homologous Chromosomes
The two Chromosomes

(q. v.) occurring in each pair in

each
derived
from
a separate parent.
Diploids,

Homologue

pair of

Homologous chromosomes,

(q. v.).

Homoplastic
Refers to organisms which have organs resembling each
other because of the evolution along similar paths, but the
organs are not Homologous, e.g., Lagomorphs and Rodents.

Homoteneity (Homotony)
The Homogeneity (q. v.) of

a Vegetation type in contrast

to that of a Stand.

Homozygous
Refers to an organism resulting from the fusion of
Gametes carrying the same genes, cf. Heterozygous.

Hook Order

social order or

rank in horned animals determined by

the aggressive use of horns.

Hopkins Bioclimatic law

See Bioclimatic law.

Horizon

(Soil)
layer of soil approximately parallel to the soil surface,
with distinct characteristics produced by soil-forming processes. See A horizon, B horizon, C horizon.

Hormone

chemical substance produced in one part of an organ176

ism and usually transported to another part where

an effect, cf. Auxin.

it

causes

Host

An

organism that furnishes food, shelter, or other beneorganism of a different species, cf. Parasite,
Mutualism.
Symbiont,

fits

to another

Hudsonicm Life Zone

One of Merriam's Life

zones, includes the northern part

of the Boreal forest and coniferous forest on mountains
farther south; southern boundary delimited by the 57.2F.

isotherm for the six hottest weeks of the year.

Humidity, Absolute

The

actual quantity of water vapor present in a given

air, usually expressed in grams per cubic meter.

volume of

Humidity, Relative

The

amount of water vapor present in

a unit portion of the atmosphere to the quantity which would
be* present when saturated, cf. Psychrometer, Hygrometer.
ratio of the actual

Humification

The

process of decay of organic material to

Humus.

Humus
(1)

Organic matter in a more or

less

stable

advanced

stage of decomposition, dark in color, with a high nitrogen

content, a carbon-nitrogen ratio near 10:1, and other chemi-

and physical properties such as a high Base exchange

capacity, water absorption, and swelling. (2) Residues in the
soil of plants and animals that have
undergone an apprecical

able degree of decomposition.

Humus, Raw
See

or.

177

Hurricane

tropical cyclone, especially one in the West Indian

with
winds of hurricane force which blow around
region;
the central calm area or "eye" which is very low in atmo(1)

spheric pressure.

(2)

Beaufort scale (q. v.), a

The

highest wind velocity on the

wind greater than about 75 miles per

hour.

Hybrid
Genetic; an organism resulting from a cross between
parents with different Genotypes (q. v.). (2) Taxonomic; a
(1)

cross

between parents of different Taxa

(q. v.).

Hybridization

The crossing or breeding of unlike

individuals to produce

hybrids.

Hybrid Segregate

form produced in the second or

later generation after

hybridization.

Hybrid

Swarm

population of organisms derived through hybridization, comprising various generations of hybrids and backcrosses; often

varying greatly,

cf.

Back-crossing.

Hybrid Vigor
See Heterosis.

Hydathode

cf.

pore or gland, usually in leaves, that exudes water.

Guttation.

Hydrarch
tats

Refers to a Succession or Sere which begins in wet habisuch as a pond. cf. Hydrosere, Xerarch.

Hydraulic Equilibrium

The

condition of absence of flow rate of water in

178

soil,

when

the pressure gradient force

the gravity force.

is

equal and opposite to

Hydric
or containing hydrogen, e.g., hydric oxide.
a
(2) Sometimes used wrongly in the sense of "wet" as
substitute for Hydrophyte (q. v.). See Hygric.
(1)

Refers

to,

Hydrochore

A plant whose Diaspores (q. v.) are disseminated primarily

by water,

e.g.,

water

Anemochore.

lilies, cf.

Hydroclimograph

graph in which monthly temperature data are plotted

against data on salinity in the form of a polygon.

Hydrocole

An

animal living in water,

Mesophyte, Xerocolous.

cf.

Hygrocole, Hydrophyte,

Hydrogen-ion Concentration
The concentration of free hydrogen

ions in a solution,

as the logarithm of the reciprocal of

the normality of free hydrogen ions in which pH 7.0 is
neutral, values higher than 7.0 indicate alkalinity, below
this acidity, cf. Reaction.

commonly expressed

Hydrography
The

study of natural bodies of water such as lakes, rivers,

and

seas, especially their physical characteristics in contrast

to the biological qualities.

Hydrologic Cycle
The cycle of the movement
precipitation to the earth

of water

and

179

from the atmosphere

return to the atmosphere

by
by interception, evaporation, run-off,
tion, storage, and transpiration.
its

infiltration,

percola-

Hydrology
The science

dealing with water and snow, including their

properties and

distribution.

Hydromorphic
(1)

in

Refers to

soil

humid

occurring in poorly drained depressions

Halomorphic. (2) Refers to cellular

cf.

regions,
features typical of Hydrophytes.

Hydrophilous
Refers to a plant that grows well in water or wet land.

Hydrophyte

A plant which grows wholly or partly immersed in water,

cf.

Hygrophilous, Xerophilous, Mesophyte.

Hydroponics
The growing

of plants so that the roots are immersed

in a water solution of nutrient salts or in some inert material

such as vermiculite which

is

supplied with a nutrient

solution.

Hydrosere

collective

term which includes

Succession beginning in water,

Hydrosphere
The parts of

cf.

all

the stages in a

Hydrarch, Xerarch, Sere.

the earth covered with water, including

streams, lakes, oceans,

cf.

Lithosphere, Biosphere.

Hydrotropism

growth response of plants to water

as a stimulus.

Hyetograph

form of self-recording Rain gage.

Hygric
Refers to a wet or moist condition of a habitat,

Hygrophilous, Xerophilous.
180

cf.

Hygrochase

seed pod that opens in

Xerochase.

humid

air

and

closes in dry

air. cf.

Hygrocole

An

animal living in a moist place,

cf.

Hydrocole, Hygro-

philous, Xerocolous.

Hygrogram

A record made by a Hygrograph.

Hygrograph

self-recording Hygrometer.

Hygrometer
An instrument
the

for

measuring the Relative humidity of

air.

Hygropetric
Refers to an organism that inhabits steep and wet rock
surfaces.

Hygrophilous

plant which grows in moist or wet places,

cf.

Hygro-

cole > Xerophilous, Mesophyte.

Hygroscopic Coefficient

The

moisture in percentage of oven-dry (100-110 C.)

that
a soil will absorb in a nearly saturated atmosweight
phere (relative humidity of 98 per cent at 25C.).

Hygroscopic Water
Water held
that

it

so firmly

by the attraction of

soil particles

can be removed only by heating above 100C.

It is

not available to plants.

Hygrothermograph
An instrument that makes

a simultaneous record of
both relative humidity and temperature, cf. Hygrograph,
Thermograph.
181

Hymenoptera
An order of insects
and ichneumon

which includes the

bees, ants, wasps,

flies.

Hyperdispersion

pattern of distribution of individuals of a species in an

area which is characterized by clumping, or the occurrence
of denser aggregations in

some

spots than in others. Syn.

Contagious distribution, Over-dispersion,

Normal

cf.

Hypodispersion,

dispersion.

Hyperparasite

An

organism that

is

parasitic

upon another

Parasite.

Hyperplasy (Hyperplasia)

An

abnormal increase in the number of cells in an

organism, e.g., certain plant galls, tumors in animals.

Hypertrophy
mean an abnormal enlargement, in rean
organism it may include both enlargement of cells
spect to
and Hyperplasy (q. v.).
Usually used to

Hypha

filament or thread-like structure of a Fungus.

Hyphal
Refers to a Hypha.

Hypocotyl
The portion
ment

of a seed or a seedling between the attachof the Cotyledons and the Radicle.

Hypodermis
The layer of

adjacent to the epidermis in certain

plants, in some species the cells are thick-walled, in others
used for water storage.
cells

Hypodispersion

pattern of distribution of individuals of a species in

182

an area which shows more even spacing than can be expected

by chance. Syn. Under-dispersion. cf. Hyper dispersion, Normal dispersion.

Hypogeal
Refers to Cotyledons which remain underground after
cf. Epigeal.
e.g., the pea seed.

seed germination,

Hypolimnion
The non-circulating body
Thermocline.

cf.

of water in lakes below the

Epilimnion.

Hyponasty
The more

rapid growth of the under side of an organ

such as a leaf than of the upper side.

Hypoplasy (Hyperplasis)
The reduction in the number

of cells in an organ,

e.g.,

in certain plant galls.

Hypsometer
An instrument

for

measuring the height of an object,

especially a tree.

Hythergraph

graphic presentation of climatic conditions in which

is the mean monthly temperature and the

one coordinate
other

is

the

mean monthly

precipitation,

183

cf.

Climagraph.

Ice

Age

A glacial

epoch in which glaciers and ice sheets occupied

areas
of
continents, as occurred in the Quaternary
large
period.

Ichthyology

The branch

of zoology which deals with fishes.

Ideograph

are

pictorial

diagram of an object in which relationships

shown between measurements

of various characteristics.

Idiobiology

The

study of the individual organism,

Synecology, Individual ecology.

cf.

Autecology,

Illuminance
Syn. Light intensity.

per square
intensity

is

unit of illuminance

foot, equivalent to the foot-candle

used.

cf.

is

the

lumen

when Light

Illumination value.

Illumination Value

The

illumination capacity or brightness of light as per-

184

ceived by the human eye; on a clear summer day

to 10,000 foot-candles at noon. cf. Irradiance.

it is

8000

Illuviation
The accumulation of material in a soil horizon by precipitation from solution or from suspension from a layer above,
cf.

Eluviation,

horizon.

Imago
The

adult, sexually

Immature

mature stage of an

insect.

Soil

which development

not complete because of

insufficient time since deposition or exposure to the action
of the physical environment and organisms on the Parent
soil in

material (q.

is

v.).

Immigrant

plant or an animal of a species which has recently

invaded an area, whose role is still uncertain, cf. Emigration.

Immigration
it

The Migration (q. v.) of an organism into an area where

did not occur previously, cf. Emigration.

Immunity
The capability
Parasite or

one of

of an organism to resist infection

its

by a

products.

Imperfect Flower

flower lacking pistils or stamens.

Impervious Soil
Refers to

or a certain layer in which the penetration

of water, and usually air and roots as well, occurs slowly
or not at all.
soil

Impoundment
An artificial lake

or pond.

185

Imprinting

when

form of rapid and stable learning in a young animal

it is exposed to a meaningful stimulus.

Inalpage

The

residence of flocks

and herds upon Alpages

(q. v.).

Inbreeding

The mating of closely related

organisms,

cf.

Outbreeding.

Incompatibility

failure or partial failure of some process which results

in lack of Fertilization. See Self-incompatibility.

Increaser

plant already present in a

increases in

community or area which

abundance under overgrazing,

cf.

Decreaser.

Increment

The

increase in the Basal area (q.

v.),

diameter, height,

volume, quality, or value of a tree or a Stand.

Increment Borer

An

instrument used for securing from the trunk of a

which shows the Growth rings.

tree a core

Indehiscent
Refers to a structure, especially fruits of plants, that do
not break open when ripe. cf. Dehiscent.

Index, Frequency
See Frequency index.

Index of Similarity
The ratio of the number

of species found in common in

two communities to the total number of species that are

present in both,

cf.

Coefficient of

community.

Index Species

An

organism that

is

so well adapted to

186

its

habitat

it

seldom occurs elsewhere, therefore useful in characterizing

environmental conditions as a living label, cf.
Autochthonous.

the

Indicator

An organism, species, or community which indicates the

presence of certain environmental conditions, cf. Exclusive
species.

Indifferent Species

species occurring in

Companion

species (q.

v.).

different communities, a

many

See Fidelity.

Indigen

An

indigenous species,

cf.

Cultigen.

Indigenous
Refers to an organism that

an

area. cf.

is

native, not introduced, in

Endemic, Exotic.

Individual Ecology
See Autecology, Idiobiology, Synecology.

Infection

The

establishment of a Parasite

upon an organism.

Infest

The
sites

establishment of an organism in numbers as para-

upon another plant or animal,

e.g.,

aphids infesting

a rose bush.

Infiltration

The

cf.

penetration of water into

Percolation.

Infiltration

soil

or other material,

Capacity

The maximum

rate of Infiltration

of conditions.

187

under a given

set

Infiltrometor

mechanism

which water

is

for measuring Infiltration into the soil in

applied by sprinkling or flooding.

Inflorescence

The
and

flower-cluster in plants, including the flowers, bracts,

stems.

Influent

An

organism which has important interactions (Reactions, Coactions) within a community, but is not a dominant.
(2) The flow of water from a channel into subterranean
(1)

storage, cf. Effluent.

Infrcmeuston
Animals which are supported by the lower surface of the
film of water on lakes and ponds, e.g., mosquito larvae, cf.
Neuston, Supraneuston.

Infusoria
Used formerly in the sense of

all

microscopic organisms
now used chiefly

occurring in infusions of organic matter;

for ciliated Protozoans (Ciliophora).

Ingestive Behaviour
The actions of an organism when eating or drinking.

Inheritance
See Heredity.

Inheritance of Acquired Characters

The outmoded theory of evolution tfyat modifications
produced during the lifetime of an individual, because of
use or disuse, new needs, or because of the direct action of
the environment are inherited by the offspring and are
cumulative with time.
Initial

The

Cause of Succession
process or agent which produces

188

denuded or

partly

denuded

areas

on which

ccologic Succession

is

initiated, e.g.,

Erosion, Deposition.

Innate Releasing Mechanism

device

(postulated)

initiates a certain reaction

in

the

nervous system

when an animal

which

receives a par-

ticular stimulus.

Inoculate

To

introduce a microorganism, virus, serum,

etc.,

into

DDT,

rote-

an organism.
Insecticide

A
none.

material used for destroying insects,

cf. Herbicide, Fungicide.

e.g.,

Insectivore
An animal in the order Insectivora, a primitive Insectivorous group in the class Mammalia, e.g., mole, shrew.

Insectivorous
Refers to an organism that

eats insects.

Insect Vector

An

by which a disease-producing organism or a

disseminated, e.g., aphids and leafhoppers trans-

insect

parasite

is

mitting plant diseases.

Insolation
Solar radiation received by the earth or other planets
from the sun, or exposure to rays of the sun.

Instar
A form in the larval development of
two moults.

insects

between

Instinct

An

inherited and adapted system of co-ordination within

the nervous system as a whole, which when activated finds

expression in behaviour culminating in a fixed action pattern.

189

Interaction

An interrelationship between organisms, between organisms and the environment, or between environmental factors,
Competition, grazing, wilting of a plant, Relative
e.g.,
humidity decreased by heat. See Coaction, Reaction.
Intercellular
Refers to the position between cells of an organism,
air-spaces

between

e.g.,

cells in leaves.

Interception

The

process by which precipitation is retained by leaves,

branches, and other organs of plants before the moisture

reaches the ground.

Interference

The

ability of a species to

by attacking
resources or

its

damage another

either directly

individuals or indirectly by harming

blocking

access

to

them.

cf.

its

Competition,

Exploitation.

Interfluve

ridge between river valleys.

Internal Drainage (Soil)

The quality of a soil that permits downward flow of

excess water through it, determined by the texture, structure,
depth to the Water table, etc. cf. Gravitational water.
Internal Environment

The

its

conditions within an organism or cell that influence

processes, e.g., the oxygen content in body fluids in ani-

mals or in air-spaces in plants.

Interspecific
Refers to relations or conditions between species,
Intraspecific.

Interspecific Association
See Association, interspecific.
190

cf.

Interspersion

The

occurrence of plant communities and

species which provide cover for animals within a limited
area. cf. Mosaic.
irregular

Intertidal Zone
See Tidal zone.

Intracellular
Refers to the location or position of a substance or
structure within a

cell.

Intraclinal

(q.

Refers to the presence of organisms such as Ecotypes

v.) within a Cline (q. v.).

Intradiel
Refers to the period of a single 24-hour day.

Intraneous

The
of

its

presence of individuals of a species toward the center

cf. Extraneous.

entire area of distribution,

Intraspecific
Refers to relations or conditions between individuals

within a species,

cf.

Interspecific.

Intrazonal Soil
A group of soils having

characteristics caused

by the

preponderant influence of local relief or parent material over

the normal influences of the prevailing climate and vegetation, cf.

Zonal

soil.

Intrinsic Cycle
See Cycle.

Introgression
See Introgressive hybridization.

Introgressive Hybridization

The

infiltration of genes of

191

one species by the

inter-

mediacy of Hybrids into another

species, resulting in the

genetic modification of the latter.

Invasion

The

Migration (q. v.) and Establishment

organism in a new location.

Inverse Stratification
The condition in which the water

just

(q. v.)

of an

beneath the

ice

in a body of water is near the freezing temperature and

within a short distance below shows a rapid rise to 3C.,

and further below a gradual

maximum

increase to

4C., or to the
cf. Thermal

temperature of the lake or pond.

stratification.

Inversion, Temperature

An

increase in air temperature with

an increase of

alti-

tude, instead of the normal decrease.

Invertebrate

An

animal lacking a spinal column,

In Vitro
Refers to experiments on

on when they

insects.

which are carried

are separated from the living organisms,

tissue cultures, cf.

In

cells, etc.,

e.g.,

In

e.g.,

vivo.

Vivo
Refers to location within the living system,

cf.

In

vitro.

Involucre

A number of closely associated bracts subtending a flower

or flower cluster.

Involution

The diminution

in the size of an organ, cf. Hyperformation of abnormal yeasts,

plasy, Hypertrophy. (2)
(1)

The

bacteria, etc.

192

Ion Exchange

The

replacement of one kind of ion by another, e.g.,

hydrogen ions replacing calcium ions in certain soil solutions.
See Exchange capacity.

lonization

The

process of ion formation.

Ionizing Radiation
Radiation that takes electrons from atoms and attaches
to other atoms, e.g., Alpha, Beta, Gamma radiation,

them

(q. v.).

Irradiance

The

receipt of radiant energy per unit area per unit of

a clear summer day solar radiant energy equals

On

time.

1.2 to 1.5 gram-calories

at noon. cf. Illuminance,

per square centimeter per minute

Light intensity.

Irradiation

The

exposure of an object to radiation such as sunlight,

Ionizing radiation,

etc.

Irritability

The

characteristic capability of

to a stimulus,

e.g.,

an organism to respond

a plant growing towards the light.

Irruption

An

abrupt, irregular increase in population

number or

size.

Isobar

line

drawn on a map or chart connecting

places of

equal barometric pressure.

Isobath

A line drawn on a map connecting points of equal depth

on the bottom of the sea.
193

Isobiochore
A line drawn on a map connecting regions
similar Biological spectra (q.

that possess

v.).

Isocies

group of Synusiae

(q.

v.)

that

show Physiognomic

similarity.

Isoflor

A line drawn
equal number

on a map connecting regions possessing an

of species within a genus or a family.

Isogamy
The production

of similar Gametes (q.

certain algae (Ulothrix), fungi,

and protozoa,

v.),

cf.

occurs in

Heterogamy.

Isogenous
Refers to organisms that occur in the same region.

Isogram
See Isotherm.

Isohaline

The
same

line or layer within a body of water

Salinity at a certain time or the same

which has the

mean

salinity

over a certain period.

Isohel

line

drawn on a map connecting

places with equal

duration of sunshine.

Isohyet

line

drawn on

map

connecting places with equal

quantity of rainfall.

Isolation

The separation of populations from other populations of

the same species by geographic, ecologic, climatic, physiologic, or other barriers, cf. Natural selection.
194

Isolation Transect
An Exclosure (q. v.) which is divided into plots, one of
which is opened to grazing each year, and another plot which
has been grazed is added.

Isonome

A line drawn on a chart connecting areas of a community

that

show equal Frequency

indices of a species.

Isophene

drawn on a chart connecting

line

areas

where events
an organism

in the life history (e.g., egg-laying, flowering) of

occur at the same time. cf. Aspection.

Isopleth

A line drawn on a map or chart connecting places having

the same value of a certain factor,

cf.

Isohyet, Isotherm.

Isopod

An

animal in the order Isopoda,

class Crustacea, e.g.,

woodlice, pillbug.

Isostasy

The

state of general

and lowland

equilibrium between the upland

areas of the earth, with indications that the

rock materials under the oceans are heavier than those under
continental protuberances, cf. Tectonic.

Isotherm

line

the same

drawn on a map or chart connecting

places with
temperature at a particular time or for a certain

period.

Isotopes
Forms or atoms of the same element that differ in atomic
weight and in the constitution of the atomic nucleus. Some
elements in nature such as radium and uranium have Radio
isotopes (q.

v.).

195

Itograph

An

instrument arranged at the entrance of a bird's nest

for the automatic recording of the

of visits made by the parents.

196

number and

direction

Jarovisation
See Vernalization.

Jordanon

Microspecies

(q. v.).

Jordan's Rule

The

generalization that fishes living in waters of low

temperatures tend to have more vertebrae than do those in

warm

waters.

Jurassic

A geological period in the Mesozoic era which began

about 165 million years ago and lasted about 30 million.

197

Kamo
A short

ridge or

mound

a stream under a glacier,

cf.

of sand or gravel desposited by

Esker.

Karst
Refers to a limestone region with a dry, barren surface
from which most or all of the drainage is through under-

ground channels.

Kar Herbage
An aggregation

of tall herbs growing in fertile soil in

hollows high in mountainous regions.

Karroo

An

open vegetation type in South Africa consisting of

succulent and sclerophyllous shrubs, where the precipitation
amounts to 3 to 14 inches annually, but which falls mostly
in the summer.

Karyokinesis
See Mitosis.

Karyotype
The gross

appearance, i.e., the size, number,

of the set of Somatic chromosomes.

198

and shape,

Key-industry (Animals)
Herbivorous animals which are so numerous that a large
of other animals are dependent upon them for food

number
(e.g.,

Copepods.

cf.

Food-chain, Pyramid-oj'-numbers.

Key Areas
is

Critical areas of range land which represent range that

likely to be overgrazed; used as criteria or indices

most

of proper use of the range.

Key Species
species of plants which because of palatability, abundance, or other characteristics may be used in estimating

Any

degree of utilization, trend, or condition of the range,

cf.

Decreasers.

Krebs Cycle
The aerobic
acid

is

portion of Respiration, in which pyruvic

oxidized, usually to carbon dioxide and water as end

products.

Kinesis

The

behaviour of an animal resulting from unoriented

reflex action of the entire animal.

Klendusity

The capability of an otherwise susceptible variety of

a species to escape infection because of the way it grows,
e.g., plants that mature early and thus escape late-season
diseases.

Klinokinesis

The random

turning movements of an organism which

it nears an unfavorable environment, cf.

increase in rate as

Klinotaxis, Orthokinesis.

Klinotaxis
A sudden movement away from an unfavorable en199

vironment,

directed

by the organism,

cf.

Klinokincsis,

Orthokinesis.

Koprophagous
See Coprophagous.

Krotovinas
one soil horizon, confrom
another
material
of
horizon; caused
sisting
transported
of
made
tunnels
by burrowing animals, especially
by filling
Irregular, tubular streaks within

rodents.

Krummholz
Scrubby, stunted growth-form of
characteristic zone at the limit of tree

200

often forming a
growth in mountains.

trees,

Lacustrine
Refers to a lake.

Lagg
See Raised bog.

Lagomorph
An animal

in the order

Lagomorpha,

class

Mammalia,

e.g. rabbit.

Lamarckism
The doctrine
characters (q. v.)

regarding the inheritance of Acquired

propounded by

Lambing Range
The area used by

J.

B. Lamarck.

bands of sheep during the lambing

season.

Land Bridge

A land connection between two bodies of land over which

migration of organisms has occurred.

Land Capability
The suitability of

land for use of some kind without

damage.
201

Land-capability Class

One

of the eight classes of land in the land-capability

ranging from (1) land that is very good for

classification,

cultivation to (8) land that

is

not suitable for cultivation,

grazing, or forestry.

Larva
The pre-adult,

usually self-feeding, but not sexually repro-

ducing form of an animal,

to the adult stage,

e.g.,

passes through metamorphosis

caterpillar of a moth, tadpole of a

frog.

Union

Periphyton

ciated in a
ent, cf.

(q. v.)

more or

less

in which the organisms are assodense growth and are interdepend-

Epiphyton.

Laterite

red,

highly weathered soil characteristic of

tropical regions such as equatorial Africa,

cf.

damp

Laterization.

Laterization
Weathering which tends to produce Laterite, essentially,
and consequent increase in alumina and
iron oxide content, and a decrease in the Base exchange
the removal of silica

capacity of the

soil. cf.

Podzolization.

laurilignosa
Laurel forests or subtropical rain forests, often with
Dicotyledonous and Gymnospermous dominants, cf. Lignosa.

Layer

The

horizontal part of a community in which the plants

are of about the same height, e.g., tree layer, herb layer.
Also applicable to depth in the soil. syn. Stratum, cf. Layering, Synusia.

Layerage
The propagation
roots

on stems

of plants by inducing formation of

that are attached to the plant.

202

Layering

The appearance of plants or plant parts, or their remains,

in horizontal divisions, syn. Stratification.
Leaching

The removal by percolating water of soluble constituents

from the soil or other material.
Leafmold
The lower
soil,

layer of the A horizon, lying on the mineral

consisting mostly of well-decomposed, finely-divided

organic material.

Leaf-size Classes

The

arbitrary groups of leaves based

proposed by Raunkiaer, in square

blades, as

on the area

mm:

of

Leptophyll

Nanophyll 225, Microphyll 2025, Mesophyll 18,225,

Macrophyll 164,025, Megaphyll larger than 164,025.
25,

Legume
(1)

plant belonging to the family Leguminosae,

The fruit of Leguminosae.

e.g.,

pea, alfalfa. (2)

Leguminous
Refers to the pea family, Leguminosae.

Lemming
One

of the small rodents in genus Lemmus or Dierostonyx, order Rodentia, of circumpolar distribution.

Length-of-day
See Photoperiodism.

Lentic
Refers to the standing-water
cf.

series; lakes,

ponds, swamps.

Lotic.

Lenticel

A pore on the surface of woody stems or roots, filled

with loosely arranged cells that permit diffusion of gases
between the atmosphere and the interior of the plant.
203

Lepidopteron

An

insect in the order Lepidoptera (e.g.)

moth.

Leptophyll
See Leaf-size

Lethal

classes.

Gene

gene

(q. v.) that

causes death of an organism.

Leucoplast

colorless Plastid in

in the Cytoplasm in plant

which starch often forms, located

cells.

Level Terrace

terrace that strictly follows the contour, in contrast to

the Graded terrace (q.

v.).

Ley

An

English term for land that

legumes, or mixtures of these.

is

temporarily under grass,

Liana (Liane)

climbing or twining plant.

Lichen

A Symbiotic

association or relationship of an alga and a

crustose, foliose, or fruticose bodies.

fungus, which forms

Law

Liebig's

The

of the

Minimum
and reproducon
the
nutrient
substance,
dependent

generalization that states the growth

tion of an organism

is

such as nitrogen, oxygen, carbon dioxide, that

in

minimum

is

available

quantity.

Life Belt

vertical subdivision of plant and animal life, determined largely by altitudinal influences, part of a Bio tic

province

(q. v.).

Life Cycle

The phases,

changes, or stages an organism passes through

204

from the

egg to death of the mature plant or

fertilized

animal.

Life

Expectancy
The average duration

of life that a given individual is

expected to live after having reached a certain age. cf.

Life table.

Life-form

The

characteristic

maturity,

e.g.,

tree,

form or appearance of a species at

herb, worm, fish. cf. Growth form,

Habitat form, Raunkiaer's life-form

classification.

Life-form Class

One
forms,

of the groups in Raunkiaer's classification of

e.g.,

Life-form

life-

Geophyte, Therophyte.

Dominance

The

condition in which several species of the same Lifedominate

a plant community, cf. Dominance, ecologic.
form
Life

Span
The maximum

duration of

life

of an individual of a

species.

Life

Table

statistical tabulation presenting complete data on the

mortality of a population, cf. Ecological longevity, Life

Expectancy.

Zone
An altitudinal

Life

distinctive faunal

Hudsonian

or latitudinal biotic region or belt with

and

floral characteristics, cf.

life zones.

Light Intensity
See Illumination value.

Light Quality

The

wave-length composition of light.

205

Alleghenian,

Llgnln
A complex organic compound in the walls of certain
especially in

woody

cells,

tissue.

Lignification

The

process of impregnating cell walls of a plant with

lignin.

Lignosa

Woody

vegetation.

Lime Requirement
The amount of standard ground

limestone needed to

change the upper 6.6-inch layer of an acre of acid soil to

lesser degree of acidity, usually stated in tons per acre.

some

Limiting Factor

The environmental
an organism
the immediate

influence by which the limit of tolerafirst reached and which therefore

tion of

is

acts as

restriction to

tions or activities or in

its

one or more of

its

func-

geographic distribution.

Limnetic
Refers to the open water of a

Limnology
The branch

pond or

lake. cf. Benthic.

of biology that deals with fresh waters

and

organisms in them.

Lincoln Index

The

use of marked animals to estimate the size of a

population.

Line-intercept Method
The sampling of vegetation by recording the plants intercepted by a measured line placed close to the ground, or by
vertical projection to the line. cf. Transect.

206

Line-plot Survey
The sampling of vegetation by means of plots of uniform
size located at regular intervals

along a

line.

Line Transect
Sampling vegetation by recording kinds of plants or
communities intercepted by a measured line. cf. Line- intercept method, Transect.

Linkage
The association

of certain characters in such a

way

that

they are inherited together, because the controlling genes

are in the same Chromosome.

Linnaean
Refers to the work or the concepts of Carolus Linnaeus.

Linneon

species according to the

nomenclature of Linnaeus, a

broad category, often containing variable forms.

Lister

An implement consisting of a double plow, in which the

shares push the soil in opposite directions, forming a series
of alternate ridges and furrows. The -Basin lister has an
attachment that forms low dams of

soil across

at intervals of 15 to 25 feet, so that basins are

the furrows

formed which

can hold large amounts of water.

List

Quadrat

A rectangular

sample area in vegetation in which organisms are merely tabulated according to species.
Liter

According to the metric system the volume of pure water,

760 mm. pressure and 4C., equivalent to 1.057

free of air, at

U.

S.

liquid quart.

207

Lithophyte

A plant growing on a rock,

e.g.,

many

lichens

and mosses.

Lithosere

on

All of the stages of a successional sequence that originated

rock. cf. Succession, Xerosere, Hydrosere.

Lithosol

soil consisting

mainly of partly weathered rock

frag-

ments or of nearly bare rock.

Lithosphere

The

earth's crust, consisting of the surface soil lying upon

is several miles thick, cf.
Hydrosphere,

the hard rock which

Biosphere.

Litter

The uppermost

organic materials, partly or not at

the surface of the soil. cf. A 00 horizon.

(1)

all

decomposed, on
(2)
The group of young born at one time by a Multiparous
animal as a cat.
Littoral
Refers to the zone in a lake or a pond that extends from
the shore to the depth at which plants are rooted. In the

ocean the zone extends to about the depth to which

wave

action,

and

Liver-fluke
A Fluke (q.

tides,

light penetrate.

v.) parasitic

on

sheep, cattle,

and other

ani-

mals, causing liver-rot.

Liverwort

plant in

usually growing

the

class

Hepaticae,

phylum Bryophyta,

in moist places, e.g., Marchantia.

Llano

A
of the

tropical

Savanna

or grassland north of forests

in South America.

(q. v.)

Amazon River basin

208

Layer
Used

at times for the

Aw

horizon

(q. v.).

Llorano

winter fog caused by the invasion of cold air during

"northers" along the shores of the Gulf of California.

Loam

containing relatively equal amounts of sand

and silt and a somewhat smaller proportion of clay. (2)
Specifically, soil material containing 7 to 27 per cent clay,
(1)

soil

28 to 50 per cent

silt,

and

less

than 52 per cent sand.

Local
Refers to a relatively small area, a few square miles as
a

maximum.

Localization

The behaviour

of an animal where

it

becomes associated

with a particular area.

Local Race

group of individuals of a species with better genetic

adaptation to a given environment than other groups, cf
Eco type.
.

Lociation

it

Climax community, differing from

in the kinds of Subdominants. cf. Faciation.
local variation of a

Locies
Similar to Lociation but applies to a Serai community.

Loess

A deposit of relatively uniform,

Silt,

presumably

transported to

Logged-over
See Cut-over forest.

209

its

fine soil material,

mostly
present position by wind.

Logistic Curve
A graph that represents the growth of an individual or
a population, typically S-shaped.

Long-day Plant

A plant that blooms under long periods of light and short

periods of darkness,

e.g.,

red clover,

cf.

Photoperiodism.

Loss-on-ignition
The loss in weight of a soil (or other material), previously dried at 100C., heated to redness hi a crucible; often
used to represent the organic content.

Lotk
Refers

to

running water

as

in

creek,

cf.

Lentic,

Rheology.

Lower Austral
See Austral

life

Lower Sonoran
See Sonoran

Zone

Life
zone.

Life

life

Zone

zone.

Luminescence
The emission

of light that
ture, cf. Bioluminescence.

Lunar Periodicity
The correlation of

is

not caused by high tempera-

activities of certain

organisms with

periods of the moon, e.g., Bioluminescence of the

fireworm at the time of full moon.

Bermuda

Lycopod

the

plant in the subphylum Lycopsida (club-mosses) in

phylum Tracheophyta,

e.g., Selaginella.

Lysimeter

An

apparatus used to collect and measure the amount

210

of water that percolates through a quantity of soil

measuring the amount of Leaching.

and

for

Lysin

substance that causes bacteria, blood corpuscles, and

other organic bodies to dissolve.

211

Macchia
Vegetation consisting of dense evergreen brush (shrubs
and small trees) in the Mediterranean region, denser than

Garique

(q. v.), similar to

Chaparral

(q. v.). Syn.

Maquis.

Macronutrient (Macrometabolic Element)

An element or a compound required by organisms

in

relatively large quantity, e.g., calcium by clams, phosphorus

salts by clovers, cf. Micronutrient.

Macrophyll
See Leaf-size

class.

Macrophytic
Refers to large aquatic plants,

e.g.,

kelps, water cress.

Macropterous
Refers to an animal with unusually large wings or
cf.

fins,

Micropterous.

Mdcrospecies
See Linneon.

Maestro

northwesterly wind

in

region.

212

the

central

Mediterranean

Mafic
Refers to ferromagnesian minerals in a rock.

Malacology
The division

of zoology that deals with mollusks.

Mallee
Scrub vegetation composed largely of various species of
Eucalyptus, about 2 to 10 meters high, in dry, subtropical
parts of southwest

and southeast

Australia.

Malthusian
Refers to the doctrine of T. R. Malthus that organisms
tend to increase in geometrical progression while the food
supply increases in arithmetical progression, so that the increase in the size of a population tends to be at a more rapid
rate than the increase in available food. cf. Competition.

Mammal
An animal

in the class

Mammalia, subphylum Vertebrata,

e.g., rabbit, deer.

Mangrove

type of vegetation that

subtropical saline, tidal mud
trees or shrubs in genera

worldwide on tropical and

consisting usually of low
Rhizopora, Avicennia, and

is

flats,

Sonneratia.

Maquis
See Macchia.

Marl

deposit of chiefly calcium carbonate, mixed with clay

or other material, and formed chiefly in fresh water lakes
by organisms such as Chara.

Marsh

A Swamp in which grasses, sedges, cattails, or rushes form

the dominant vegetation,

cf.

Bog. Moor.

213

Marsh Gas
See Methane.

Marsupial

An

e.g.,

animal in the subclass Marsupalia,

kangaroo, opossum.

class

Mammalia,

Massif

principal, relatively

uniform mountainous mass with

peaks on top.

Mass Selection
The

choosing of individuals that possess a certain charcommon from a population such as a corn field,

acteristic in

and then bulking the seeds or propagules

for later planting.

Mast
Nuts such

as acorns, beechnuts,

sense, especially

Mature

and

others, in a collective

the nuts are used as food for animals.

Soil
in good adjustment with environmental
many regions with well-developed horizons,

soil that is

conditions, in
cf.

when

Podzol, Chernozem.

Meadow
A grassland,
for hay.

cf.

mowed

Pasture, Range.

Mean Sample

usually in a low, moist area; often

Tree
form and that is
volume of the other indi-

tree selected for its representative

average hi diameter, height, and

viduals of the species in a stand.

Mechanical Analysis

laboratory procedure for determining the percentages

of clay, silt, and sand in a sample of soil.

Mediterranean Climate
The climatic conditions

that prevail in lands bordering

214

the Mediterranean Ocean, characterized by hot, dry

and cool, rainy winters.

summers

Medium-height Grass
In the classification of grasses according to height, the
class that ranges from 2 to 5 feet in height, includes Midgrasses (q.

v.). cf.

Highgrass, Shortgrass.

Megagea Realm
One of the three classes of the earth's fauna, which
includes the Ethiopian, Oriental, Palearctic, and Nearctic
regions,

cf.

Neogea, Notogea.

Megaphanerophyte

A group of plants in Raunkiaer's life-form classification

which includes trees, lianas, and epiphytes over 30 meters
high.

Megaphyll
See Leaf-size

classes.

Megaspore
The

two kinds of spores produced by plants such

and the Spermatophytes (q. v.). cf. Microstore.

larger of

as Selaginella

Megatherm
An organism

that requires continuously high tempera-

and according to some usage abundant moisture,

sugarcane, cf. Mesotherm, Microtherm, Hekisto therm.
tures,

e.g.

Nleiosis

The two

successive divisions of the nucleus in

Chromosome number
the Haploid (q. v.)

halved, from the Diploid

number.
is

Melanism
The unusual development
215

which the
(q. v.) to

of a dark pigment in

an

Melanocyte
Cells in certain animals

that contain black pigment,

melanin, as in the chameleon. The contraction of the cells

makes the animal appear

light in color, expansion

makes

it

appear dark.

Melliphagous
Refers to an organism that feeds on honey.

Mendelian
Refers to Mendel's laws (q.

v.).

Mendelian Population

group of individuals of a species that share in a

common Gene pool through reproduction, cf. Species,
Syngameon.

Mendelism
The knowledge

of inheritance according to Mendel's

laws.

Mendel's Laws

The

rules according to which characteristics of organisms

are inherited as stated by Gregor Mendel, such as characters

or factors (genes) act as units, dominance and recessiveness

of characters, the segregation of Alleles during meiosis, and
the independent assortment of alleles in each Gamete.

Mercator's Projection
A method of mapping
are drawn as straight lines

in which the parallels of latitude

of the same length as the equator.

Meristem

A tissue in plants that

concerned with division to form

located in various places such as root tips, stem

new

cells,

tips,

and buds.

cf.

is

Cambium.

Meroplankton

An

of

its

organism that is in the Plankton

life cycle, cf. Holoplankton.

216

(q. v.)

during part

Merriam's

Life

Zones

series of belts

criteria of

or Life zones

(q. v.)

temperature according to C.

based originally on
Hart Merriam. See

Alleghanian, Carolinian, Hudsonian, Sonoran, Transitional,

Tropical Life zones.

Mesa

flat

or nearly

flat

table land with steep sides.

Mesarch
Refers to a successional series that begins in a moderately
cf. Hydrarch, Xerarch.

moist habitat,

Meseta
The greatly

eroded, broad plateau in the interior part

of Spain, crossed by a few mountain ridges.

Mesic
Refers to environmental conditions that are

moisture supply,

cf.

medium

in

Mesophytic, Hygric, Xeric.

Mesolimnion
See Thermocline.

Mesophanerophyte
One of the groups

of plants in Raunkiaer's life form

classification, consisting of trees, lianas, and epiphytes, 8 to

30 meters

tall.

Mesophyll
The palisade and sponge
lower epidermises in a

cells

between the upper and

leaf.

Mesophyte

plant that grows in environmental conditions that are

in moisture conditions, e. g., corn.

medium

Mesophytic
Refers to a Mesophyte.

217

Mesosaprobic
Refers to an aquatic environment in which the oxygen
considerably reduced and in which
position of organic materials is taking place,

content

is

much decomcf.

Catarobic,

Polysaprobic.

Mesotherm
An organism
erate moisture,

that requires moderate

e. g.,

corn, hickory,

cf.

warmth and mod-

Megatherm, Micro-

therm, Hekistotherm.

Mesotrophic
Refers to a

swamp

supplied with a moderate amount of

nutrients.

Mesozoic
One of the
era,

great geological eras, preceding the Cenozoic

about
205 million years ago and lasted about 130
began

million years; divided into the Triassic, Jurassic, and Cretaceous periods.

Metabolic Water

The

water obtained from the chemical breakdown of

foods by some organisms such as the clothes moth.

Metabolism
The sum total

of chemical processes occurring within

an organism or a portion of it, includes Anabolism and

C atabolism (q.v.). Basal metabolism is the rate of expenditure of energy while an animal is at rest. cf. Autotrophic,
Heterotropkic.

Metabolite

Any

substance that plays a part, directly or indirectly,

in Metabolism.

Metagenesis
See Alternation of generations.

218

Metalimnlon
See Thermocline.

Metamorphosis
The change of an

animal from one form to another in its

postembryonic development, e. g., larva of an insect to a
pupa.

Metaxenia
The differential

effect of pollen
fruit.

from

different varieties

on the development of the

Metazoan
An animal
ticellular

in the group Metazoa which includes all mul-

animals as opposed to the unicellular Protozoan

(q.v.).

Meteorograph
An apparatus for

automatically recording simultaneously

two or more meteorological elements.

Meteorology
The study that

deals with physical processes occurring in

the atmosphere such as precipitation, winds, and temperature.

Methane

CH

often called marsh gas, an odorless, inflammable

4
and
gas,
explosive when mixed with air. Develops from decomposing organic matter in marshes and in coal-mines.
,

Micelle (Micella, Micell)

A particle composed of complex molecules that forms the
units of structure in
lose

and

many

organic substances such as cellu-

starch.

Microassociotion

The abstract class or type of community in which similar

Microstands are grouped, e. g., microstands of certain kinds
219

of annual weeds that form a zone around carpenter-ant

in a shortgrass association or community-type.

mounds

Microbe

A Microorganism

(q. v.).

Microclimate

The
cf.

climatic conditions within a Microhabitat (q.

v.).

Local.

Microcommunity

A small Community (q. v.) such as the plants and animals

living in

and on a decaying stump

in a forest.

Microcosm

miniature world, organisms plus the environmental

cf. Ecosystem.

conditions,

Microdissection

The procedure in which organisms or cells are studied

through a microscope by means of a mechanically operated
apparatus.

Microhabitat

A small Habitat (q. v.),

between clumps of grass.

e.

g.,

a tree

stump or a space

Micro-micron

A metric measure,

one-millionth part of a Micron

(q. v.).

Micro-millimeter

metric measure, one-millionth part of a millimeter.

Micron

metric measure, one thousandth part of a millimeter.

Micronutrient

chemical substance required by an organism in very

small quantity,

ment,

boron by many

plants, cf. Essential eleMacronutrient, Vitamin, Deficiency disease.

e.g.,

220

Microorganism

An

organism that

is

microscopic in

size, e. g., bacteria,

protozoa.

Microphagous
Refers to an animal that feeds on particles that are very
its own size, e.g., certain whales feed-

small in comparison to

ing on plankton.

Microphanerophyte

group of plants in Raunkiaer's life-form classification,

includes trees, shrubs, lianas, and epiphytes, two to eight
meters

tall.

Microphyll
See Leaf-size

classes.

Microphyllous
Refers to a plant that has small leaves.

Mictopterous
Refers to a

hind wings,

cf.

fish

with small

fins

or to an insect with small

Macropterous.

Microrelief

Minor differences in topography such as small mounds

or pits with differences in elevation of about three feet or
less.

Microsere

series of successful stages that

occur within a micro-

habitat such as a tree-stump.

Microsome

minute, RNA-rich particle in the cytoplasm of a

cell,

the center of protein synthesis.

Microspecies

Species that is less inclusive than the Linneon (q.

similar to Subspecies (q. v.). Syn. Jordanon.

221

v.),

Mlcrospore

The

smaller of two kinds of spores produced by plants

such as Selaginella and the Spermatophytes,

e.

g.,

pollen

group of plants that occupies a Microhabitat

(q. v.).

grains.

Microstand

A
cf.

Stand.

Microtherm

An

organism that can develop in cool and short summers,

barley, spruce trees, cf. Megatherm, Mesotherm,
Hekistotherm.
e. g.,

Microtome

An

instrument for cutting very thin sections of tissue

for microscopic study.

Mictium

heterogeneous mixture of species such as occurs often

between two kinds of stands.

in a transition zone

Midgrass

grass

which

is

two to four

five feet

Medium-height

or

feet tall, in contrast to a tallgrass

more

tall,

e. g.,

Koeleria

cristata. cf.

grass, Shortgrass, Highgrass.

Migrant

An

organism that

is

undergoing Migration

(q. v.).

Migration
(1) The movement

of a plant or one or more of its parts,

such as fruits, from one area to another. (2) The movement
of an animal beyond its regularly occupied geographic location or

Home

range

(q. v.). cf.

Emigration, Immigration, In-

vasion.

Migrule
See Diaspore.

222

Milacre

An

part of an acre, containing

often used as a plot 6.6 feet square.

area one-thousandth

43.56 square

feet,

Millibar

unit of atmospheric pressure, 1000 millibars repre-

sents a pressure of about 29.53 inches (750.1

mm.)

of mer-

cury.

Millicurie
One-thousandth part of a Curie

(q. v.).

Milligram
One-thousandth part of a gram.
Milliliter

One-thousandth part of a

liter.

Millimeter
One-thousandth part of a meter, 0.0394 inch.

Millimicron (mu)
One-thousandth part of a Micron

(q. v.).

Mima-type Microrelief

type of microrelief characterized by low mounds or

soil pimples, named after the mounds in Mima
prairie in

western Washington.

Mimesis
The kind

of behaviour in which like elicits like, involv-

ing hereditary patterns.

Mimetic
Refers to mimicking behaviour,

cf.

Allelomimetic.

Mimicry
(1) Batesian:

The kind

species escapes death by

to an inedible species.

of behaviour in which an edible

close resemblance in appearance

(2) Mullerian: The kind of be-

its

223

havior in which both species are inedible but are similar

in appearance, so avoidance learned by predators in tasting
one is extended to the other. The term mimicry is often
restricted to the former.

Mineralization

The
forms,

decomposition of organic substances to mineral

e. g.,

proteins to nitrates, phosphates, etc.

Mineral Soil
Soil

composed mainly of inorganic materials and with

amount of organic material.

only a relatively low

Minimal Area
The smallest

area

on which a community develops

Characteristic species-combination (q.

its

v.).

Minimalraum, Minimiareal
See Minimal area.

Minimum, Law of
See Liebigs law of the

minimum.

Minimum Quadrat Area

For a given number of samples in a stand the size of
quadrat in which the Species-area curve (q. v.) becomes
nearly horizontal, and the use of a larger size to secure
greater accuracy is not justified by the time and labor involved.

Minimum Quadrat Number

For a given

number

size of

quadrat used to sample a stand the

of quadrats at which the

number

of species-number

of quadrats curve becomes nearly horizontal, and the use of

more quadrats to secure greater accuracy is not justified by
the time and labor involved. See Species-number curve.

Minor Element
See Essential element, Micronutrient.

224

Miocene

geological epoch which began about 28 million years

lasted about 16 million years, in the Tertiary pe-

ago and

riod of the Cenozoic era.

Mississippian Period

geological period in the Paleozoic era (q. v.), which

began about 280 million years ago and lasted for about 25

million years.

Mistral

cold, northerly

ranean

wind along the northwest Mediter-

coast, especially

during winter.

Mite

An

animal in the order Ac&rina, class Arachnida, phylum

Arthropoda; including both free-living and parasitic forms.

Mitochondrion

minute body in the cytoplasm in

cells,

the chief loca-

tion of respiratory enzymes, syn. Chondriosome.

Mitosis

The

ordinary division of a nucleus that includes the

longitudinal doubling of chromosomes to form pairs of

chromatids, separation of each pair to form two daughter
nuclei; so a constant number of chromosomes is maintained.

Mitotic
Refers to Mitosis.

Mixed

Forest
composed of

forest

ally at least

trees of

two or more

species, usu-

20 per cent of the trees are of other than the

leading species.

Mixed Prairie
An extensive grassland

type lying west of the tall-grass or

True prairie in North America, consisting of a mixture of
tall-, short-, and midgrasses, and other herbaceous plants.

225

Mixotrophic
Refers to an organism that

and Heterotrophic

(q. v.), e. g.

is

both Autotrophic

(q. v.)

Insectivorous plants.

Model
The organism

that in

Mimicry

is

imitated.

Modification

A
istic

non-inheritable, Phenotypic variation of a characterof an organism, caused by the environment, e. g., taller

growth of a plant in the shade than in the sun.

cf.

Acquired

character.

Moisture Equivalent

The

percentage of moisture retained by a small sample

of saturated soil after being subjected to a centrifugal force

1000 times that of gravity for a definite period of time, usually one-half hour.

Moisture Stress

The

tension at which water

is

held in the

soil.

Moisture Tension

The

force at

which water

is

held in the

soil.

Mollusk

An

organism in the large phylum Mollusca,

e. g., snail,

oyster.

Monadnock
An erosion remnant such as a hill or a mass of rock rising
above the surrounding land.

Monandry
The mating

of a female with only one male, or the

presence of only one stamen in a flower.

Monoclimax (Theory)
As postulated by

F.

Clements, ecologic succession will

226

in time culminate in a single Climax (q. v.) within a climatic

cf.

region,

Polydimax.

Monoclinous (Monoclinic)
Refers to plants that have perfect flowers, i. e., stamens
and pistil in the same flower, e. g., a rose flower, cf. Diclinous.

Monocotyledon

A vascular plant

in the subclass Monocotyledoneae, class

Angiospermae (flowering plants), e. g., grasses, orchids, cf.

Dicotyledon.

Monoecious
(1) Refers to a plant with some flowers containing only
stamens and other flowers with only one or more pistils on
the same plant, e. g., corn. cf. Dioecious. (2) A unisexual

animal or plant,

cf.

Hermaphrodite.

Monogamy

The mating

opposite sex. cf.

of an animal with only one

member

of the

Polygamy.

Monogynoys

The mating

of a male with only one female,

cf.

Poly-

andry.

Monohybrld

cross or

Hybrid resulting from the mating of parents

one character, cf. Dihybrid.

differing in only

Monolith

(Soil)

A sample of a vertical section of a soil profile a few inches

thick,

removed from the

possible,

cf.

soil

with as

little

disturbance as

Profile (soil).

Mono
Refers to an organism that subsists

227

on a few or only one

kind of food,

e. g.

many caterpillars,

cf.

Steno-, Euroky.

Monoploid
See Haploid.

Monotopic
Refers to a single area such as in the restricted area of
distribution of a species.

Monotreme
An animal

in the primitive order Monotremata, eggrestricted to the Australian faunal region,

laying mammals,
e. g.,

platypus.

Monsoon

A wind system

that reverses

its

direction with the season,

mostly in southeast Asia.

Monsoon

Forest

A tropical

forest of deciduous trees in regions where seasons of heavy rainfall alternate with long droughts.

Montane
Refers to mountains.

Moor (Moorland)
Primarily high-lying, unenclosed land occupied by
heather and other ericaceous dwarf shrubs, including boggy
areas, cf.

Bog, Heath, Marsh, Swamp.

Mor

A layer of Humus material,

or both lying on the mineral

Moraine
The accumulation

usually compacted or matted

soil. cf.

H-layer.

of rock material by a glacier, occurs

in various topographic forms such as ridges or more level

areas according to the manner of formation. Various kinds
are lateral, terminal, medial,

and ground moraines.

228

Mores
The

general behavioural attributes of motile organisms,

or groups of animals possessing particular ecological characteristics.

Morphogenesis
The origin and development
of an organism or one of

Morphology
The study

its

of the form

and structure

parts.

of the form, structure,

and development of

organisms.

Morphology
The

(Soil)
constitution of the soil including texture, structure,

and other

properties.

Mosaic

pattern of vegetation in which two or more kinds

of communities are interspersed in patches, e. g., clumps of
shrubs with grassland between. (2)
symptom of some kinds
(1)

of virus disease.

Moss

(1)

plant in the class Musci,

phylum Bryophyta.

(2)

Bog.

Muck
An

organic soil consisting of fairly well decomposed unrecognizable organic material that is finely divided, dark in
color, and with a relatively large content of mineral matter.

Mulch

natural or artificial layer of plant residue or other

on the soil surface, cf. Dust

material such as sand or paper

mulch.

Mulch Tillage
Working

of the soil so that plant residues are left

the surface.

229

on

Mulgo

A scrub

thicket consisting mostly of Acacia.

Mull

layer of

Humus

less friable, slightly

that

is

or not at

transition to the mineral soil

granular in structure, more or

matted, and with a gradual
or.
below, cf.

all

Multiparous
Refers to an animal that produces more than one young
at birth,

cf.

Uniparous.

Multiple Use

The policy of using a resource in several ways such as the

use of forests for the production of timber, forage, water
supplies, and game animals, and also for recreation.
Multivoltine
Refers to an organism that has
ing a single season,

cf.

several generations dur-

Univoltine.

Muskeg

in the northern part of North America characan

abundance usually of Sphagnum moss and a
by
or
lesser
abundance of shrubs and low trees such as
greater

Bog

terized

black spruce.

Mutagen
An influence
e. g.,

that induces Mutation (q. v.) in organisms,

Ionizing radiation.

Mutant

An

organism, characteristic, or gene resulting from

Mu-

tation.

Mutation

A sudden,

an organism resulting
alterations of the structure

inheritable variation in

from changes in a Gene, or in

or number of Chromosomes.
230

Mutualism
The kind
biosis that

is

of interspecies relationship, Coaction, or Symobligatory and beneficial to the two or more

participating organisms,

e.

g.

a fungus and an alga in a

lichen.

Mutuality

The relationship where mutual benefit or dependence

occurs because of the proximity of organisms to one another.

Mycelium
The mass of Hyphae

(q. v.) of a

fungus,

e. g.,

bread mold.

Mycetophagous
Refers to an organism that eats fungi,
bolon that eats Hyphae.

e. g.,

a Collem-

Mycetozoa
See Myxomycete.

Mycology
The branch

of botany that deals with fungi.

Mycorrhiza
The symbiotic
certain plants,

cf.

relationship of a fungus with the roots of

Mutualism, Endotrophic, Ectotrophic.

Mycorrhizomata
The association of

a fungus with a Rhizome.

Mycothalli

The

association of a fungus with a Thallus.

Mycotrophic
Refers to a plant with Mycorrhiza.

Myriapod
An animal

in the group Myriapoda comprising classes

Chilopoda (centipedes) and Diplopoda (millipedes), phylum

Arthropod*.
231

Myrmecodomatia
Structures

on plants in which

ants or termites live.

Myrmecolous
Refers to an organism that lives in ant or termite galleries.

Myrmecophilous
Refers to plants that are inhabited by ants or termites.
cf.

Trophobiosis.

Myrmecophobous
Refers to plants that repel ants or termites.

Myrmecophyte

A plant that has structures adapted for the shelter of ants

or termites and usually also has extrafloral nectaries or

glands producing nutritious substances, e. g. Acacia spp.

Myxomycefe

slime mold.

An

organism possessing both animal and

in the
plant characteristics,
phyta in the Fungi, syn. Mycetozoa.
classified

232

phylum Myxomyco-

Nanism
The dwarfed

appearance of plants, as at tree-line in

mountains.

Nanophanerophyte

A subdivision of the Phanerophytes (q.v.)

in Raunkiaer*s

life-form classification, comprising shrubs 0.25 to 2 meters in

height.

Nanophyll
See Leaf-size

classes.

Nannoplankton
Very minute Plankton (q. v.), those that pass through
meshes of a No. 20 silk bolting cloth (0.03 to 0.04 mm.).

Nastic

Movement

response in plants caused by a diffuse stimulus (not

received from a definite direction) or when the response to

a diffuse or lateral stimulus

irritable organ,

pudica

when

e.

it is

determined exclusively by the

g., drooping of the leaves of Mimosa
touched, cf. Tropism.
is

233

Natality

The production

of offspring by organisms.

Natatorial
Refers to the

swimming

capacity of an organism.

Natural Area

An

area of land in which organisms and geological procundisturbed by man, with as few controls as pos-

esses are
sible, cf.

Primitive area.

Natural Selection

The

agent of evolutionary change by which the organisms

possessing certain characteristics in a given environment give

rise to more offspring than those lacking such characteristics.
cf.

Drift, genetic; Mutation.

Nature Reserve
See Natural area.

Nature Sanctuary
See Natural area.

Neap

Tides

The

lowest tides during a month, occurring about the

time of the moon's

first

and

last quarters.

Nearctic

One

of the faunal regions of the earth, in the realm

Megagea, includes North America except the tropical part

of Mexico.

Necrosis

The death of an organism or one of its parts.

Nectar

The sweet liquid secreted by special glands in flowers or

in other parts of plants, attractive to insects, cf. Nectary.
Nectariferous
Refers to a flower or plant that produces nectar.

234

Nectary

gland in a flower or on a vegetative organ that produces nectar.

Nekton
The strong-swimming

animals in water,

e.

g.,

fish.

cf.

Benthos, Plankton.

Nematode
An animal
minthes,

e. g.,

Nematoda, phylum Nemathelhookworm, eelworm in potatoes.

in the class

Nee-Darwinism
The doctrine of modern
etics

with Natural selection

evolution that combines Gen-

(q. v.).

Neogea
The
tropical

faunal realm, containing only one region, the Neowhich includes South and Central America and the

tropical parts of Mexico,

cf.

Megagea, Notogea.

Neo-Lamarckism
The theory of evolution

that includes

fications of the doctrines of

Lamarckism

modern-day modi(q. v.).

Neolithic

The

cultural stage, beginning about ten thousand years

in
human history, following the Paleolithic, during
ago,
which cultivation of plants and domestication of animals

were

started.

Neoplasm
An abnormal

increase in the

number

of cells in

some

part of an organism, often malignant.

Neoteny
The occurrence

of larval or other juvenile characters in

the adult stage of an organism, or the presence of an adult
character in the larval stage, e. g., larval form of the adult

235

female

cf.

glowworm,

Paligenesis,

Caenogenesis,

Paedo-

genesis.

Neotropical
See Neogea.

Nephometer
An instrument
is

for measuring the percentage of sky that

overcast.

Nephoscope
An instrument
the

movement

for

measuring the direction and speed of

of clouds.

Neritic
Refers to the portion of the sea lying above the continental shelf, usually to a depth of 200 meters, cf. Oceanic
province, Pelagic, Littoral, Sub littoral.

Nested Quadrats

An arrangement of placing Quadrats in one area so that

the size of the area sampled becomes progressively larger,
to determine the proper size of quadrat to use for the particular

kind of vegetation.

Net-Assimilation Rate

The

rate of increase in dry weight of the

whole plant in

relation to the unit leaf-area or unit leaf-rate.

Neural
Refers to the nervous system or to a nerve.

Neuston
The organisms

in a collective sense that are associated

with or dependent upon the surface film of water,

mosquito

e.

g.,

larvae.

Neutralism

The

occurrence of two or more populations in an area

and neither influences the other.

236

Granular, compacted snow at the head of a glacier, or

similar

snow elsewhere,

syn. Firn.

Niche
(1) Ecological niche:
its activities

vironment,
abiotic environment.

the role of an organism in the enand relationships to the biotic and

(2) Habitat niche: the specific part

or smallest unit of a Habitat occupied by an organism, cf.

Biotope.

Nidicolous
Refers to young, undeveloped birds that remain in the
nest for a time after hatching.

Nidifugous
Refers to young, undeveloped birds that leave the nest
soon after hatching.

Nitrification
The oxidation of ammonia and ammonium compounds
to nitrites and then to nitrates by certain bacteria, cf. Nitro-

gen

cycle.

Nitrogen Cycle

The

circulation of nitrogen, chiefly by means of organisms from the inorganic nitrogen in the atmosphere to ni-

and protoplasm in plants and animals,

and
return
to nitrites and nitrates, cf. Nitrogen
ammonia,

trates, into

to

proteins

fixation, Nitrification.

Nitrogen Fixation

The
by

assimilation of free nitrogen of the atmosphere

microorganisms in the soil or by bacteria in the nodules

of certain plants, especially legumes,

into organic nitro-

genous compounds.

Nitrophilous
Refers to plants that grow well in soil that
nitrogen, e. g., many barnyard weeds.

237

is

rich in

Nivation

kind of erosion caused by the action of snow,

e.

g.

Solifluction.

Nocturnal
Refers to night time.

cf.

Crepuscular, Diel, Diurnal.

Nodule

A structure formed on the roots of most legumes and a

few other species containing bacteria that carry on Nitrogen
Fixation.

Nodum
An

abstract unit of vegetation such as Association, Sociation, and Alliance; corresponds to Taxon in Systematic*.

Nomad
A member of a group, especially of primitive people, who
change their dwelling place frequently.

Nomina Conservanda
Names of organisms whose usage is maintained by agreement of systematists although the names may be contrary to
the rules of nomenclature.

Non-available Water
The amount of water
permanently,

cf.

in the soil

when

a plant wilts

Wilting.

Non-reactive Factor

An

environmental factor such as weather conditions

which are not influenced by the density of individuals in a
population, but may produce increasingly adverse effects
with increasing density,

cf.

Density-independent factor, Den-

sity-dependent factor.

Normal Dispersion, Normal

The

Distribution

distribution in an area of individuals of a population that is at random.

238

Normal Erosion
The Erosion that occurs on land under natural environmental conditions not disturbed by human activities, cf.
Accelerated erosion.

Normal Spectrum
See Biological spectrum.

Norther (Norte

in Central America)
northerly wind, especially a strong one, that begins
suddenly during the colder half of the year in the region
from Texas southward, including the Gulf of Mexico and
the western Caribbean.

Notogea
One

of the three continental fauna! realms. It includes

the Australian region (q.

v.). cf.

Megagea, Neogea.

Nuciferous
Refers to nut-bearing plants.

Nunatak

A body of land, such as a mountain, projecting at some

time above a mass of ice and snow, or above a glacier.
Nurse Crop
See

Companion

crop.

Nutation

circular or spiral

movement

of the growing portions

of plants such as stems or tendrils.

Nutrient (Plant)

Any

substance absorbed by a plant that

is

used in

its

Metabolism.

Nyctinasty
The movement
tion of night

of a plant organ in response to alternaas in clover leaflets.

and day

259

Nyctitropism
See Nyctinasty.

Nymph
A stage
the larval

in the Metamorphosis of
and adult forms.

240

certain insects

between

Obligate Parasite

A Parasite that cannot attain complete development inde-

pendent of

its

Host.

Oceanic Province
The portion of the ocean seaward from

the Continental

shelf, having a depth greater than 200 meters,

cf.

Neritic.

Oceanography
The science dealing with all aspects of the ocean; physical conditions, plant and animal life, etc.; sometimes restricted to the study of physical conditions only.

Oecology
See Ecology.

Oesophagous
See Esophagous.

Oestrus (Estroys) cycle

The period in mature females in many kinds of mammals when the desire for mating occurs; it varies in length,
is

controlled by hormones,

and

bodily changes.

241

is

often accompanied by

Offset

A short,

basal stem

by which some plants propagate.

Oleaginous
Refers to the production or presence of oil in a plant
organ,

e. g.,

olive fruit.

Oligocene

The

geological epoch near the middle of the Tertiary

period in the Cenozoic era which began about 39 million
years ago and lasted for about 11 million years.

Oligosaprobic
Refers to an aquatic habitat that is high in content
low in dissolved organic matter, and with very
little decomposition of organic substances that are present,

of oxygen,
cf.

Catarobic, Polysaprobic, Mesosaprobic.

Oligotrophic
Refers to ponds or lakes that are low in content of basic
nutritive substances for plants, lacking a distinct stratification of dissolved oxygen in summer or winter, cf. Eutrophic.

Ombrophilous
Refers to plants that endure
are easily wetted.

much

rain,

Ombrophobous
Refers to plants that do not endure
unwettable leaves.

with leaves that

much

with

rain,

Omnivorous
cf.

Refers to an animal that eats both plant and animal food,

Carnivorous, Herbivorous.

Ontocline

A gradation in phenotypic characteristics such as color or

form appearing at different times in the life cycle of an
may be related to the Ecocline (q. v.).

mal,

242

ani-

Ontogeny
The development

of an individual, or a part of

the Zygote to the adult,

cf.

it,

from

Phytogeny.

Oogamy
Sexual reproduction by means of eggs and sperms,

cf.

Heterogamy.

Open Community

in which the plants are more or

which invasion may readily occur.

community

tered, in

Open

less scat-

Pollination

Pollination (q.

v.)

by wind,

insects, etc.,

not directly by

man.

Open Range
An extensive

grazing area

on which the movements

of

livestock are unrestricted.

Open Woodland

A parkland type of vegetation in which trees do not form

an open canopy.

Optimum

(Conditions)

The

range of conditions which is most favorable for an

organism, or for a certain function of an organism, cf. Ecological amplitude.

Order
In plant and animal Taxonomy, a group or Taxon of
e. g. Resales. In phytosociology, a group of
similar Alliances. In classification of soils, the highest category comprising Zonal, Intrazonal, and Atonal soils.
related families,

Ordovician

geological period in the early

pan

of the Paleozoic

which began about 425 million years ago and

about 65 million years.
era,

243

lasted

Organ

A distinct part of a plant

or more particular functions,

Organelle
Any part

or animal which carries on one

e. g.,

a leaf,

wing of a

bird.

of a cell of an organism.

Organic Matter

(In Soil)
Materials derived from plants or animals, much of it in
a more or less advanced stage of decomposition, cf. Humus.

Organic

Soil

composed mainly of organic matter on a volume

containing 20 per cent or more on weight basis, e. g.,

soil

basis;

Muck,

Peat.

Organismic (Organismal)
a

Refers to the concept that a group of organisms such as

qualities of a higher level of organization

community has

than the constituent organisms have individually; changes

occurring in a community are related more to the qualities
of the group than to those of the individual plants and
animals.

Oriental Region

One

of the four continental faunal regions in the realm

Megagea; it includes tropical Asia and the associated continental islands.

Ornithology

The

division of zoology that deals with birds.

Ornithophilous
Refers to flowers that are pollinated by birds such as the

hummingbird.

Orogenesis

The

process of

mountain formation by changes in the

earth's crust.

244

Orographic
Refers to mountains, or to relief characteristics of the
land.

Ortet

The

plant from which

derived,

cf.

members

of a Clone (q. v.) were

Ramet.

Orthogenesis

The

trend in the evolution of organisms in a particular

direction for a long time. cf. Genetic drift, Sewall Wright
effect.

Orthokinesis
The random movements

of an organism that decrease

in rate from one part of an environmental gradient to another part, e. g., a meal worm moving from the moist part

of a gradient

and congregating in the drier

part. cf. Klino-

kinesis, Klinotaxis, Photokinesis.

Orthopterous

An

insect in the order Orthoptera, e.

g.,

cricket, grass-

hopper.

Orthoselection

The

trend in the evolution of organisms which

is

in a

particular direction under the influence of selection,

cf.

Orthogenesis, Natural selection.

Ortstein

strongly compacted, indurated layer (Pan) of soil in

particles are cemented together with iron and or-

which the

ganic matter.

Osmoregulation
The adjustment

in the osmotic concentration of solutes

in fluids in organisms to environmental conditions,

when eels migrate from salt to fresh water.

245

e.

g.,

Osmosis
The diffusion

of a solvent (especially water) across a differentially permeable membrane separating two solutions or
separating a solution and a solvent.

Osmotic Concentration
The concentration of salts

in a solution.

Osmotic Pressure (of a Solution)

The rating or index of potential maximum pressure
which can develop in a given solution when it is exposed to
Osmosis.

Osteology
The study

of the development

and nature of bones

in

vertebrate animals.

Oued

valley that contains water in rainy seasons (Arabian).

Outbreak
The occurrence
sufficient

number

of an organism in large

to cause serious

numbers or

in

damage over an appreci-

able area.

Outbreeding
The mating
cf.

of individuals that are not closely related,

Inbreeding.

Outcrop

geological stratum that

the earth.

is

exposed on the surface of

Outwash, Glacial
Material carried by streams of melt water from a glacier
and deposited in the form of plains, deltas, and Valley
trains.

246

Ovary
The

portion of the Pistil or Carpel of a flower that

contains one or more ovules (q. v.). (2) The organ in female
(1)

animals that produces the egg or ovum.

Overdispersion
See Contagious dispersion.

Overgrazing
Grazing so intensively that it reduces the capacity of
plants to continue production of forage and also causes deterioration by damaging plants or soil or both. cf. Undergrazing.

Overpopulation

population-density in excess of the capacity of the en-

vironmental resources to supply the requirements of the individual organisms, usually accompanied by a high mortality
rate because of inadequate nutrition, insufficient shelter, and
increased predation, disease, or parasitism, cf. Malthusian.

Overstocked
Refers to stands of trees in which the large number
retard growth. (2)
population of animals in which the

(1)

may
number

in excess of the resources of the habitat to provide

shelter, cf. Fully stocked.

is

food and

Overstocking

The placing of more livestock on a range than its resources can support through the grazing season without
Overgrazing.

Overstory

The

layer of trees in a forest that forms the Canopy,

cf.

Understory.

Overturn
The spring and

fall

circulation in lakes induced

247

by the

wind when thermally

become mixed,

different strata

cf.

Epilimnion.

Oviparous
Refers to an animal that lays eggs in which embryos
show little or no development, e. g., most fishes, cf. Viviparous, Ovoviparous.

Ovipositer

specialized structure in insects for depositing eggs.

Ovoviparous
Refers to an animal that keeps ova or eggs within the
until they are ready to hatch, requiring internal fertilization, as in birds, cf. Oviparous, Viviparous.

body

Ovule
The

structure within the Ovary of a flower that after

it develops into a seed.

Fertilization of the egg within

Ovum
A

female Gamete

Oxbow Lake
A more or less
a

meander of a

(q. v.)

or egg.

pond formed when

from
the
main stream.
separated

semicircular lake or

river

is

Oxidation-reduction Potential

The potential of a given material, in comparison with

other materials, to release electrons (oxidation), or to receive
electrons (reduction); symbolized
tial.

Oxylophyte
See Acidophilous.

Oxyphilous
See Acidophilous.

248

by E h

syn.

Redox poten-

Oxyphobous
See Basophilous.

Oxysere
The stages
soil that

is

of a successional series that began in water or

appreciably acid.

cf.

Succession, Hydrosere.

249

Paddock

small Enclosure in a grassland.

Poedogenesis
Reproduction occurring in
cf. Neoteny.

larval or other

young

stages

of an animal.

Paedomorphosis
The evolutionary

process in which a character of an immature stage of an organism appears in the adult stage, cf.

Neoteny.

Palafability

The
shown

acceptability of food by domestic or wild animals as

by their preferences; in range management often used

for utilization of forage, especially the proper degree of use

under good management,

cf.

Proper use

factor.

Palearctic

One

of the four continental faunal regions in the realm

Megagea (q. v.). It includes Eurasia north of the Tropics and

the northernmost part of Africa.

250

PQ looDoto ny
The study of fossil

plants, cf. Paleontology, Paleozoology.

Paleocene
The earliest

geological epoch in the Tertiary period of

the Cenozoic era, which began about 75 million years ago
and lasted for about 17 million years.

Paleoecology

The

study of Ecology of former geological periods.

Paleogenic (Palaeogenic)
See Paleozoic.

Paleolithic
Refers to the period of

human

history characterized by

food-gathering, fishing, and hunting, without

and by the use of stone implements.

cultivation;

Paleontology

The

study of the

means of

fossils, cf.

life

of former geological epochs by

Paleobotany, Paleozoology.

Paleozoic

One

of the major geological eras, preceding the Mesozoic,

which began about 505 million years ago and ended about

205 million years ago.

Paleozoology
The study of animal

fossils, cf.

Paleontology, Paleobotany.

Palingenesis

The

appearance during the development of an organism

of stages or structures which occurred in earlier forms during its evolution, cf. Caenogenesis, Recapitulation.

Paludel
Refers to marshes.

251

Palynology
The study

and other microfossils, especially

and other bodies of water, to deterstrata and the kind of plant life existing

of Pollen

from deposits in
mine the age of

lakes

in former periods,

cf.

Paleobotany.

Pampas
Extensive grasslands in South America, particularly in
Argentina, large portions of which are

now

cultivated,

cf.

Prairie, Steppe, Veld.

Pampero

suddenly arising, violent, southwesterly wind on the

Pampas of South America, most prevalent from July to September.

Pan

layer in the soil that is strongly compacted and

(1)
indurated, or with a very large clay content, cf. Ortstein.
shallow, basin-like depression without vegetation or
(2)
outlet for drainage.

Panclimax
According to F. E. Clements two or more related climaxes that have the same life-form, common genera of dominants, and the same general climatic factors, cf. Formation.

Pandemic
Refers to something which has a wide occurrence such as
a disease.

Panmixis
The wide

interbreeding of individuals of a population,

where each individual has the potential capacity of mating

with any other individual.

Pannage
The

feeding of swine in woods, or the food such as

252

acorns that

is

secured.

term used in England

especially.

Pantono

fresh-water or brackish

marsh in Argentina.

Pantograph

drafting instrument used in copying maps or charts,

adapted for charting the location and area of plants in a

Quadrat

(q. v.).

Papagayo

tral

violent northeasterly

wind

of the Pacific coast of Cen-

America.

Papilionaceous
Refers to the butterfly-like flower of

many

species in the

pea family, Leguminosae.

Paramo
An alpine
land, in high

America,

cf.

type of vegetation, or the sparsely vegetated

mountains in the Andes and in northern South

Tundra.

Parang

type of mixed vegetation composed of species differing

in height, which occurs on areas
following the repeated cutting of forest in southeast Asia.

Parasitism

The

interaction or Coaction in

which one or more

or-

ganisms, the Parasite, benefits while feeding upon, securing

shelter, or otherwise injuring one or more other organisms,
the Host; often the term
cf.

is

restricted to nutritive relations,

Symbiosis, Saprophyte.

Paratonic
Refers to movements of plants such as tropic or nastic
movements induced by an external stimulus, cf. Tropism,
Nastic movement.

253

Parch Blight

The kind of injury to plants, especially evergreens that

have been exposed to strong, drying winds in winter.

Parenchyma
(1) A common

tissue in the soft parts of plants consisting

of thin-walled, cubical cells, e. g. pith, fleshy fruits. (2) The

loose tissue that forms a large part of the body of flat-worms.

Parent Material (Soil)

The C horizon (q. v.) of
Parent Rock (Soil)
The rock from which

the

soil.

the parent material of the soil has

been formed.

Parkland
The type

of landscape in which trees occur in clumps in

grassland.

Parthenocarpy
The development
zation, e.

g., as

of the fruit of a plant without Fertili-

in the banana.

Parthenogenesis

The development

of the egg of an organism into an em-

bryo without Fertilization,

cf.

Apomixis.

Pasturage
Herbage of an area taken by an animal when

grazing, the

yield of a Pasture.

Pasture

An

area of vegetation used for grazing, sometimes restricted to areas of cultivated land which, have been seeded

and then used

for grazing,

cf.

Range.

Patabiont

An

animal that spends

its

normal

forest floor stratum.

254

life

in the debris of the

Poland
(1)

montane

grassy slope (Ceylon). (2)

grassy slope

with a moderate supply of moisture, resembling a Savanna.

Pathogen

An

organism or virus that causes

Pathology
The study

disease.

of diseases.

Patocole

An animal that spends a regular part of its normal

outside of the forest floor but lives transiently in it.

life

Patoxeite

An

animal that occurs accidentally in the

litter of

the

forest floor.

Pattern

The arrangement formed by

the occurrence of indivi-

duals or groups of organisms in an area, such as Contagious

dispersion, Hypodispersion,

and Normal dispersion

(q. v.).

Peat

An

organic soil consisting of partially decomposed or-

ganic remains which can be identified as to the kind of constituent plants. It accumulates in water or under wet conditions, cf.

Muck.

Peck-dominance
The dominance

of one bird over another in a flock, applied also to other animals, cf. Social dominance.

Peck-order

The
flock,

order of dominance of some birds over others in a

applied also to other animals.

Peck-right
The dominance of one bird over
255

all

the others

iri

flock.

Ped

An

individual soil aggregate occurring naturally.

Pedalfer

The kind
downward

and iron oxides move

and in which no accumulation

of soil in which alumina

in the soil profile

of calcium carbonate occurs,

cf.

Pedocal, Laterite.

Pedigree

A record

of the ancestry of an individual.

Pediment

A gradual slope covered with scattered rock adjacent to a

mountain in semi-arid and arid

regions.

Pedocal

A type of soil in which a layer of accumulated carbonates

occurs,

cf.

Pedalfer, Laterite.

Pedogenic
Refers to effects caused by soil factors.

Pedology
The science

dealing with

soils.

Pedon

Community dependent on

the bottom in lakes,

cf.

Benthos.

Pelagic
Refers to the open water of the ocean, lacking association with the shore or the bottom, cf. Abyssal, Neritic, Benthic, Littoral.

Peneplain

land surface worn

level so that

most of

Penicillin
An Antibiotic

it

down by

erosion to almost Base

appears as a plain.

(q. v.)

produced by the mold Penicillin

notatum.

256

Pennsylvania!!

geologic period in the latter part of the Paleozoic era

which began about 255 million years ago and

lasted for

about

25 million years.

Perched Water
The body of free ground water

in a zone of saturation,

separated from an underlying body of ground water by an

unsaturated layer of material.

Percolation

The downward movement

of water in the

in saturated or nearly saturated

Perennate
The continuance
as in a

Rhizome or

soil,

especially

soil, cf . Infiltration.

of life in an organism

from year to year

seed.

Perennial

plant that lives for three or

Biennial.

more

years, cf.

Annual,

Perfect
Refers to flowers containing one or

more stamens and

pistils.

Perianth

The

flower parts surrounding the stamens and petals; the

petals and/or sepals of a flower; much reduced in some
flowers.

Periodicity

The

repeated occurrence of events at fairly frequent and

Phenology.

regular intervals, cf. Aspection,

Periphyton

The

assemblage of organisms attached to surfaces subcf. Benthos, Plankton.

merged
in water, above the bottom,

257

Permafrost
Permanently frozen ground in

arctic

and subarctic

re-

gions.

Permanent Pasture
Grazing land that remains under grazing use for many
years, cf. Rotation Grazing, Range.

Permanent Quadrat

marked sample area or quadrat

vegetation

is

(q. v.)

recorded over a period of

many

in which the
years.

Permanent Wilting Percentage

The quantity o water in the soil on
when

plants growing in

it

a dry weight basis

have reached the condition of

permanent Wilting.

Permeability

The

(1)

property or condition of the

soil that relates to

the passage of water or air through it. cf. Percolation. (2)

The rate of diffusion of molecules of a substance through a

membrane,

cf.

Osmosis.

Permeant

An

animal in a

motility,

e. g.,

terrestrial

community which has

great

a bird.

Permian
The latest

geological period in the Paleozoic era which

million years ago and lasted for about 25
about
230
began

million years.

Pessimum
The conditions

mum

of the environment outside of the Optiwhich an organism can endure, cf. Ecological ampli-

tude.

Pesticide

An

agent or substance that destroys pests,

or
insecticide.
cide

258

e. g.,

a fungi-

Petal

One

of the parts of the Corolla of a flower.

Petiole

The

stalk of a leaf.

Petran
Refers to the Rocky Mountains.

Petrification
The formation of fossils by the replacement of organic
substances in dead organisms by minerals.

P*

soil

measure of the energy by which a

dried at 100-110

has a

pF

soil

holds water;

of 7.0, the tension de-

creases as the water content increases.

pH

measure of the acidity or alkalinity of a solution, or

H or
to 14.
ions, ranging from
Values above 7 are alkaline, below 7 are acid. cf. Reaction
the concentration of

OH

(2).

Phoge
See Bacteriophage.

Phagocyte

A cell that engulfs bacteria or other particles,

e. g.,

white

corpuscles in the blood.

Phagocytosis

The

engulfing of particles by a Phagocyte.

Phanerogam
See Spermatophytes.

Phanerophyte
One of Raunkiaer*s

life-form classes (q. v.) in which the

buds or other perennating parts are more than 25 cm. above
the ground, especially trees and shrubs.

259

Phenology
The study
life

plant
e. g.

and

of the periodic phenomena of animal and

their relations to the weather and climate,

the time of flowering in plants,

cf.

Periodicity, Aspec-

tion.

Phenotype
The expression

of the characteristics of an organism as

determined by the interaction of its genie constitution and
the environment, cf. Genotype, Ecad.

Phloem
The tissue
which

is

in plants that conducts foods such as sugar

performed especially by the sieve tubes.

Phoresy
The transport
carried

by

of one organism

by another,

e. g.,

mites

insects.

Phosphorescence
See Bioluminescence.

Photeolic
See Nyctinasty.

Photic

Zone

The upper

portion of bodies of water into which light

penetrates in sufficient intensity to influence plants or animals,

cf.

Aphotic zone.

Photogenic
cf.

Refers to the capacity of a substance to produce light,

Bioluminescence.

Photokinesis

The

undirected locomotion of

response to light,

many lower

accomplished by
ence the speed of their movements,

kinesis.

260

organisms in

their capacity to influcf.

Phototaxis, Ortho-

Photometer

An

instrument for measuring the intensity of

Photon
One

of the particles in a

beam

light.

of radiant energy,

cf.

Quantum.

Photonasty
The response
stimulus,

e. g.,

of an organism or organ to a diffuse light

closing of oxalis flowers in the evening.

Photoperiod

The

duration of light during a 24-hour period.

Photoperiodism (Photoperiodicity)

The response of plants and animals to the relative duration of light and darkness, e. g. a chrysanthemum blooming
under short days and long nights.
Photosynthesis

The synthesis of carbohydrates from carbon dioxide and

water by Chlorophyll using light as energy with oxygen as a
by-product.

Phototaxis

The

directed

movement

to a light stimulus,

cf.

of a motile organism in response

Photokinesis.

Phototrophic
cf.

Refers to organisms that can obtain energy from sunlight,

Autotrophic, Heterotrophic, Chemotrophic.

Phototropic

The growing

or turning of an organ of a plant when unequally illuminated, toward the light of greater intensity.

Phragmosis
The process
an ant closing

of opening or closing holes by animals,

entrance to the nest in a plant stem.

its

261

e. g.,

Phreatophyte

plant that absorbs its water from a permanent supply

in the ground, e. g., willows along a stream.

Phycology
See Algology.

Phylad

A phylogenetic group of closely related species.

Phylloclade
See Cladophyll.

Phylogeny
The evolutionary development and

relationships of a
of
such
rodents
as
or
organisms
group
species of rose. cf.

Ontogeny.

Phylum
One

of the major subdivisions used in classifying plants

and animals,

e. g.,

Tracheophyta (vascular

plants), Arthro-

poda (arthropods).

Physiognomic Dominance
Dominance (ecologic) (q. v.) caused by the similarity of
a number of species in a certain life-form rather than because of greater cover, number, or size of one or a few
species, e. g., a weed patch consisting of many species of

annual weeds similar in form.

Physiognomy
The appearance

of vegetation as determined by the lifeplants, e. g., a grassland, pine forest.

form of the dominant

Physiographic Climax
See Climax.

Physiography
The branch of

physical science that deals with the physical features of the earth, cf. Geomorphology.

262

Physiological Drought

The

when

a plant wilts or suffers

from insufficient water although the habitat contains ample
water, cf. Aridity, Cold desert.

conditions that obtain

Form

Physiological

See Biological race.

Physiological Isolation

The condition of organisms that have become isolated

because of their physiological requirements rather than because of other kinds of Barriers, cf. Isolation.
Physiology
The branch

of biology that deals with the functions

on by plants and animals.

and

processes carried

Physogastry
The condition
comes swollen,

some insects in which the body

and white, as in some beetles.

in

soft,

be-

Phytocide

effect

chemical substance that exerts a differential killing

within a crop, e. g., one variety but not the other

varieties killed

by

DDT in a barley crop.

Phytocoenosis

The

totality of plants in a stand of vegetation, the entire

plant Community,

cf.

Biocoenosis.

Phytocoenosfics

The term

Gams

preferred by

in place of Plant sociology.

Phytogeography
See Plant geography.

Phytograph

A polygonal diagram

that expresses several kinds of

characteristics such

munity
quency index,

size classes,

as

and

basal area

a certain species of tree in a forest.

263

com-

numerical abundance,

on various axes

fre-

for

Phytometer

plant such as the sunflower, used to measure environ-

mental conditions.

Phytopathology
The study of plant

diseases.

Phytophagous
See Herbivorous.

Phytoplankton
The plants occurring

in Plankton (q.

v.), e. g.

diatoms.

Phytosociology
See Plant sociology.

Phytotron

An

extensive set of rooms used for growing plants under

controlled environmental conditions.

Pioneer

plant, animal, or community that first invades a bare

area, e. g., willows on a newly formed sandbar.

Pisciculture

The growing

of

fish.

Pistil

See Carpel
Pistillate
Refers to the

pistil, e. g. pistillate flower.

Pitting

The making

of shallow pits or depressions, especially in

rangeland, with an offset disk or pitting machine, in order

to retain rain water or snowmelt.

Pituitary

The

gland inside the skull of vertebrates which

264

is

of

major importance in the secretion of Hormones, many of

which control the activity of other Endocrine (q. v.) glands.

Plagioclimax

A type of

(q. v.) vegetation which is the result of

a
biotic
climax, e. g., an apparently stable
activity,
continued
caused
mowing or grazing, cf. Disby
community

Climax

man's

climax, Proclimax,

Sub climax,

Plagiosere, Ser climax.

Plagiosere

A Sere (q. v.) deflected from its undisturbed course by the

constant intervention of
grazing,

man

in such activities as burning,

in a Plagioclimax.

and mowing, resulting

Plain

An

extensive tract of nearly level or gently undulating

land that

is

usually occupied by grassland vegetation.

Plane Table

surveying instrument used for making a sketch-map

of a small area.
,

Planimeter

An instrument used to determine the area of a plane

ure or object such as a leaf by tracing the boundaries.

fig-

Plankter (Plankt, Planktont)

An

individual organism in the Plankton (q.

Plankton
The floating

or weakly

v.).

swimming animal and plant

or-

any depth in lakes, ponds, streams, or

ganisms
often
seas;
microscopic in size.
occurring at

Planosol

An

Intrazonal group of soils with eluviated surface hori-

zons underlain by clay pans or fragipans, developed on nearly

flat or gently sloping uplands in humid or subhumid climates,

cf.

Eluviation.

265

Plant Association
See Association.

Plant

Community

See Community.

Plant Cover
See Cover.

Plant Formation
See Formation.

Plant

Geography

The

science that deals with the geographic distribution

and the causes of their distribution and dispersal,

of plants
syn.

Phytogeography, Synchorology.

Plant Nutrient

The
in

substances or elements absorbed by a plant and used

metabolism, e. g., nitrates, phosphates, cf. Essential

its

element.

Plant Unit

The part of a vegetatively propagating plant which is considered as a unit in analyzing vegetation, e. g., each stalk of
plant that has rhizomes.

Plantigrade

An

e. g.,

animal that walks on the entire bottom of the

feet,

bear, man.

Plant Sociology

The

study of plant communities, including their origin,

composition, structure, characteristics, distribution,

namics, and classification, syn. Phytogeography.

dy-

Plasmagene
Gene-like, non-Mendelian carriers of hereditary characlocated in the Cytoplasm.

ters,

266

Plasmodium
The mass of

cytoplasm containing many nuclei that is

enclosed by a single plasma membrane, occurring in Slime

molds

(q. v.). cf.

Syncytium, Coenocyte.

Plasmolysis

The shrinking of the Cytoplasm from the

caused by osmosis of water out of the cell.

cell

wall,

Plasticity

The

(1)

capacity of an organism to adapt itself to various

be
(2) The capacity of a soil to

environmental conditions.

changed in shape under applied stress and to retain the impressed shape after removal of the stress.

Pkutid

A
e.

g.,

protoplasmic body in the Cytoplasm in

Chloroplast, Leucoplast, Chromoplast.

cells of plants,

Maya
Undrained,

flat,

barren basins that are usually dry and

often saline, in arid and semiarid regions.

Pleistocene

The

geological epoch preceding the Recent in the Quaternary period of the Cenozoic era, which began about one
million years ago and lasted for about one million years.

Pleomorphic
Refers to an organism that has two or more forms in
life cycle, cf.

its

Polymorphism.

Pleuston

one-layered

community

within bodies of water,

cf.

of plants that float

on or

Plankton.

Pliocene

The

latest geological

epoch in the Tertiary period of the

267

Cenozoic era which began about 12 million years ago and

about 1 1 million years.

lasted for

Ploidy

number

Refers to the
e. g.,

Diploid, Polyploid

of sets of

Chromosomes

in a cell,

(q. v.).

Plot

An

area of land that

purposes, in

is

studied or used for experimental

which sample areas are often

located.

Plowpan

compacted layer formed in the soil immediately below

the depth of plowing, syn. Plowsole.

Plumule
The portion

of the embryo of a seed, above the place of

attachment of the cotyledons, consisting of the stem tip and
a few embryonic leaves.

Pluvial
Refers to rain.

Pluviilignosa
Vegetation that includes rain forest (Pluviisilvae) which
is

dominated by evergreen broad-leaved

trees,

and rain bush

(Pluviifruticeta).

Pneumatophore

special structure on an aquatic or marsh plant that

(1)
extends above the water making a direct connection of the
tissues with the aerial environment. (2) Air sacs exposed to

the aerial environment occurring in some aquatic insects.

Pocosin
A bog

in shallow, undrained depressions in savannas in

the southeastern part of the United States.

Podzol (Podsol)

A Zonal group

of soils having surface organic layers and

268

mineral horizons above gray, leached horizons

upon illuvial, dark brown horizons; developed under coniferous or mixed forests or heath vegetation in cool-temperate,
thin, organic

moist climates.

Podzolic
Refers to

soils that

have part or

all

of the characteristics

of Podzol.

Podzoiization

The

process by which soils are depleted of bases, becomacid, and develop leached surface layers from which

ing more
clay

is

removed,

cf.

Laterization, Calcification, Solonization.

Poikilotherm

An animal
ture which

is

that lacks capacity to control its body temperaapproximately that of the environment, e. g.,

a frog.

Point-contact

Method (Point-frame)

A technique for determining the area of herbage cover by

listing the

number

of times that various species are touched

Numerous contacts are used in

by the point of a rod or pin.

each Stand or Plot.

Poisson Distribution
See Normal dispersion.

Polar Front

The boundary between

the

warmer

air of

the cold air of a polar region

lower latitudes,

cf.

Warm

and

front.

Polarity

The property of an organism to respond differently in its

various ends or in contrasting parts of its body to stimuli.
Polder

An area
dams or

of land reclaimed

from the

dikes, especially in Holland.

269

sea or

from a lake by

Pollen

The

Microspores which give

phytes in seed plants,

cf.

rise to the

male Gameto-

Pollination.

Pollen Analysis

The

identification

and determination of abundance

pollen in soil deposits, particularly in peat.

cf.

of

Palynology.

Pollen Profile

A tabular or graphic expression of the occurrence of various kinds of pollen in deposits of peat or other materials at
different depths.

Pollen Spectrum

The

expression in percentage of the kinds of pollen in

one sample of a Pollen analysis (q. v.).

Pollen Tube

The

tubular growth, male Gametophyte containing the

sperms, produced by a pollen grain when it germinates on
the stigma and extends into the style of the pistil of a flower.

Pollination

The

transportation of pollen

by wind,

insects,

or other

agent from an anther to a stigma in flowering plants; usually

by wind from a pollen-bearing cone to the Ovw/e-bearing
cone in conifers.

Pollution
Contamination of a habitat with substances which make
it less

favorable for organisms.

Polster

plant form resembling a cushion, consisting of closely

packed stems, dead leaves, and often roots, e. g., many saxifrages, mosses.

Polyandry
The mating
cf.

of a single female animal with several males,

Monogynous.
270

Polyclimax
The concept
vegetation in an

that several Climaxes (q. v.) constitute the

area as the result of Succession (q. v.).

Polyembryony
In animals the development of more than one embryo
from a fertilized egg; in plants the development of more than
one embryo within a single Ovule of a plant.

Polygamy
The mating
cf.

of one male animal with several females,

Monogamy, Polygyny.

Polygonal

Soil

The surface configuration of

gons, common in arctic regions.

soil

characterized

by

poly-

Polygyny
Mating by Polyandry or Polygamy

Polymorphism
The presence

(q. v.).

of several distinct forms

in a species,

particularly within a certain habitat or population,

cf.

Pleomorphic.

Polyploid

An

organism or a

Diploid number

of

cell

that contains

Chromosomes per

more than the

cell.

cf.

Haploid,

Tetraploid.

Polysaprobic
Refers to an aquatic habitat that

is

characterized by con-

siderable decomposition of organic material and low concentration or absence of free oxygen, cf. Catarobic, Mesosa-

probic, Oligosaprobic.

Pol/topic
Refers to a species that occurs in
especially to Discontinuities (q. v.).

271

more than one

area,

Polytypic
Refers to a species that occurs in various forms in different parts of

its

range.

Pome
A multicarpellate fruit in which
ing the ovary

is

the fleshy part surround-

formed from the receptacle,

e.g.,

apple

fruit.

Population

A group

smaller

of interacting individuals of the same species or

in a common spatial arrangement.

Taxa

Population Cycle

The

recurrent changes in the size of a population from

low to high numbers and the return

the cycle of the snowshoe hare.

Population Density
The number of individuals

to

low numbers

as in

in a population per unit area.

Population Dynamics

The

totality of

changes that take place during the

life

of a population.

Population Pressure

The combined

forces of the individuals of a population

upon the organisms in a

ment, cf. Biotic pressure.

Pore Space
The fraction

of the

occupied by solid

community and upon

volume of

soil

the environ-

or rock that

is

not

particles.

Porosity

The

state of

matter which contains Pore spaces.

Postadaptation

The

increase in Adaptation in a Preadapted organism

after its invasion into a given environment.

272

PostclKmax

Climax community (q. v.) that requires more mesic

conditions than obtain generally in the region where it is
present, often considered a remnant of a former widespread
Climatic climax (q. v.).
Potential, Biotic
See Biotic potential.

Pothole

hole formed in rock by the grinding action of a stone

motion by a stream.

kept in

Potometer

An
by

instrument used to measure the absorption of water

plants.

Prairie
Grassland vegetation, particularly the extensive tract of
nearly level or rolling land in North America occupied by
tall grasses.

Prairie Soils
A Zonal group of
ing through brown
to five feet,

climate,

cf.

soils with dark surface horizons gradto lighter colored parent material at two
under tall grasses in a temperate, humid

formed
Chernozem.

Preadaptation
The possession by an organism of characteristics that
enable it to survive when exposed to new ("prospective")
the possession of a disease-resistant gene in
an organism not yet exposed to the disease, cf. Postadaptation.
conditions,

e.g.,

Preboreal Period
See Boreal period.

Precambrian
The geological time

preceding the Cambrian period, the

oldest period of the Paleozoic era.

273

Precipitation

general term for all forms of falling moisture insnow, hail, sleet, or modifications of them.
rain,
cluding
(1)

(2)

The quantity of water

that

in which water as a liquid

upon land or water.

is

is

precipitated. (3)

The process

discharged from the atmosphere

Precipitation-effectiveness Ratio

The total amount of precipitation for a certain period of

time divided by the total amount of evaporation, both in
liquid form.
Precipitation Rose
A radial diagram expressing the amounts of precipitation
by months or other intervals of time.

Preclimax

Climax community

(q. v.) that

occurs usually in

more

Xeric conditions than obtain generally in the region where

it is present, often considered a
stage in succession preceding
the full development of a climax,

cf.

Postclimax.

Precocial
Refers to young animals that do not need parental care
after birth or hatching, cf. Altricial.

Predation

The

behaviour of animals, Predators, in killing other

animals, Prey.

Predator

An

animal that attacks other animals, Prey,

e.g.,

a fox

that kills mice or other prey.

Predominant
Refers to organisms that are of outstanding abundance
or conspicuous importance in a community.

Preferendum
The preferred or

"selected" conditions of a motile organ-

274

ism when exposed to a gradient of one or more environmental conditions, cf. Optimum, Minimum, Pessimum,
Tolerance.

Preferential Species
Species in Class 3 of Braun-Blanquet's classification of
Fidelity (q.

species occurring

v.);

more or

but predominantly or with greater

community.

less

vitality,

abundantly,
in a certain

Premature Grazing
The grazing of vegetation

before the most important

have
forage species
grown sufficiently, or before the soil has
become dry and firm enough, to prevent cumulative injury
to the range,

cf.

Range

readiness.

Prescribed Burning

The

use of

fire

under control

to

improve growth condi-

tions in vegetation.

Presence

The

degree of occurrence of a species in Stands of a

Community-type,

cf.

Constancy.

Pressure, Biotic
See Biotic pressure.

Prevernal
Refers to early spring, cf Aspcction.
.

Prey

An

dator

animal that

(q. v.), e.g.,

is attacked and killed

by another, Prea ground squirrel killed by the coyote as a

predator.

Primary Succession
v.) beginning on a bare area such as a lava
not previously occupied by plants or animals, cf.
Secondary succession.

Succession (q.

flow,

275

Primate

An

animal in the order Primates which includes lemurs,

monkeys, apes, man, and others, in the

class

Mammalia.

Primeval
Refers to vegetation, geological features, and other
natural phenomena, in original condition, before any modification has been made through the influence of modern

man,

e.g.,

a primeval forest.

Primitive
Refers to an organism, organ, or behaviour that

is

char-

an early

stage in evolution, not specialized or

advanced in evolution.

acteristic of

Primitive Area
An area in which conveniences for transportation and
living are kept simple and not modernized, cf. Natural area.

Primordium

part of an organism where growth

is

initiated.

Prisere
See Primary succession.

Proclimax
According to F. E. Clements any community that resembles a climax in permanence or extent such as a Postclimax and Preclimax (q. v.). cf. Subclimax, Plagioclimax,
Disclimax.

Producer

An

organism that can

utilize radiant

energy to synthesize

organic substances from inorganic materials,

cf.

Consumer

organisms.

Productivity
(1) The total quantity of organic material produced
within a given period by organisms, or the energy that this

276

represents such as gram-calories per square centimeter per

year. (2) The innate capacity of an environment to produce

plant and animal life. (3) The capacity of a soil to produce

a certain kind of crop under a defined set of management
conditions.

Profile (Soil)

vertical section of soil

the parent material,

cf.

through

all

its

horizons into

horizon.

Profundal (Zone)

The body

of deep water

and the bottom of

the depth of effective penetration of light,

cf.

lakes

below

Abyssal.

Proliferation

The

rapid development of new growth such as the production of new parts from buds, offsets, and other organs.

Proliferous
Refers to the ready vegetative reproduction by means of
organs such as buds and offsets; the development of leafy
shoots from a flower or flower head or other organ.

Propagate

To

increase the

number

of plants vegetatively by bulbs,

conns, cuttings, or other plant parts.

Propagule
Any part

of a plant that when it is separated from a plant

new individual, cf. Diaspore, Disseminule.

will give rise to a

Proper Stocking
The number of individual
utilizes the

livestock in a grazing unit that

herbage without permanent deterioration of the

vegetation or the

soil. cf.

Overstocking.

Proper Use Factor

The maximum percentage

of the total

amount

of annual

forage production of a species in a given area within easy

277

reach of the livestock that

may be

grazed without permanent

deterioration of the plants of this species or associated

species nor of the soil. cf. Overstocking.

Protandrous
is

Refers to a flower that produces pollen before the stigma

receptive, e.g., fireweed; or to animals that produce sperms

sooner than eggs are produced by the

certain nematodes. cf. Protogynous.

same animal,

e.g.,

Protective Coloration

The

concept that coloration in animals benefits the

individual by affording concealment from predators or from

prey animals, cf. Mimicry.

Protein

A nitrogenous
and complex

organic

structure,

compound

of large molecular size

formed from amino

acids.

Proterozoic

The geological era preceding the Paleozoic which began

about 2,000 million years ago and lasted for about 1,500
million years.

Prothallus

The vegetative structure of the Gametophyte (q. v.) generation that is part of the life cycle of ferns and their allies,
cf. Thallus.
Protista

group including

all

one-celled organisms such as one-

celled algae, bacteria, and protozoans; suggested as a third

kingdom of living organisms, the other two being plants
and animals.

Protocooperation

An

interaction between organisms that is mutually beneficial but not obligatory to those participating, not appli-

278

cable to conscious cooperation of

human

beings,

Com-

cf.

mensalism, Symbiosis.

Protogynous
is

Refers to a flower that produces pollen when

receptive to pollen, cf. Protandrous.

its

stigma

no longer

Protonema
The branched

filament of the Gametophyte (q. v.) generation that develops from a spore in mosses, and produces

leafy branches.

Protoplasm
The living material

and
and cytoplasm.

in cells of animals

differentiated into nucleus

plants, usually

Protoplast

The

organized protoplasmic contents of a cell, used particularly in plants to distinguish the cell wall from the parts
within.

Protozoan

An animal, unicellular or non-cellular in the

Protozoa.
Provenance
The place

phylum

of origin of seeds or other Propagules.

Psammolittoral

The

sandy shore of a lake.

Psammon
The assemblage of organisms that live in the water in
the interstices between sand grains in the Psammolittoral
(q. v.).

Psammophyte

A plant

that grows in sandy

279

soil. cf.

Hydrophyte.

Psammosere
All the stages of a successional series or Sere (q.
inating in sandy soil. cf. Hydrosere.

v.) orig-

Psychrometer

An

instrument used to measure the Relative humidity of

the atmosphere by means of the effect of temperature differences of the wet and dry bulb thermometers, cf. Hygrometer.

Pteridophyte

Vascular plant in one of the subphyla of the phylum

Tracheophyta, exclusive of the seed plants, e.g., fern, clubmoss, horsetail.

Public

Domain

Land for which the title was originally vested in the

Government of the United States by virtue of its sovereignty.
More than half of the original public domain has been
granted to

states,

The remainder

homesteaders, railroads, or has been sold.

set aside for national forests, national

is

parks, national monuments, Indian reservations, grazing districts, and similar purposes.

Puddled

(Soil)

Dense, massive
ing no regular

soil artificially

compacted when wet, hav-

structure.

Puddling

The

process of destroying the structure of the soil during

which the porosity and permeability are reduced.

Pulse

The sudden

appearance of a great abundance of plant

Plankton.

Puna
The cold, bleak portions of the high plateau region in
the central part of the Andes in South America.
280

Pupa
The

stage in the

and adult

larval

Metamorphosis of an

insect

between the

stages.

Pupation

The
when

process during the Metamorphosis of an animal

the Pupa is formed.

Pure Line

A
a

series of generations of individuals

Homozygous

which orginated in

ancestor.

Puszta

A
cf.

grassland type of vegetation in the Plains of Hungary,

Steppe, Prairie.

Pyramid of Numbers
The concept of C. Elton

that in most Food-chains the

number

of individuals decreases in each succeeding stage,

numbers
of animals occur at the base, a few large ones
large
at the top.

Pyrheliometer

An

instrument for measuring solar radiation.

Pyrrhic
Refers to

fire.

281

Qio Rule, Van't Hoff Rule

The rate of response of a process in an organism is often

doubled or more for each increase of 10C. of temperature
within certain limits.

Quadrat

sampling area, originally square, most commonly one

square meter, used for analyzing vegetation. A major quadrat
is usually 10 meters
square, cf. Plot, Permanent quadrat.

Quadruped
An animal

with four

feet, e.g.,

cow.

Quagmire
Soft, wet,
cf.

boggy ground which quakes or yields underfoot,

Bog.

Quantum

unit of energy that

is

Quaternary
The latest

emitted by a Photon

(q. v.).

geologic period of the Cenozoic era which

about
one
million years ago, includes the Recent and
began

Pleistocene epochs.

Quotient of Similarity
See Index of similarity.

Race

Biology.
Population within a species that differs in
one or more inherited characteristics from other populations
(1)

but not

sufficiently distinct to rate as a

rapid movement

Taxon

(q. v.). (2)

of the tide through a narrow channel.

Rachion

The line where waves break in lakes, the places where

wave action and undertow cause the greatest turmoil.

Rod
The

dose or unit of ionizing radiation absorbed by tissues

of an organism, equal to 100 ergs of energy per gram.

Radiation
(1)

source,

The
e.g.,

emission and transmission of energy from a

Ionizing radiation

electromagnetic waves such as

See Adaptive radiation.

(q.

v.),

solar radiation

by

gamma-rays.

(2)

light, x-rays,

Radicle

The lower end of the axis of the embryo in a seed and

which develops into a root during germination.
283

Radioactivity

The

spontaneous breakdown of certain atomic nuclei

usually resulting in the emission of radiant energy in the
form of Alpha or Beta particles, or Gamma rays.

Radioautograph

representation of an object containing radioactive

Isotopes (q. v.) such as a leaf on a photographic negative to
show the distribution of the radioactive material.

Radiocarbon Dating
Determination of the age of organic remains such as
long-buried wood by measuring its radioactivity caused by
C 14, which has a half-life of 5568 years and begins to break
down upon the death of organisms.

Radioisotope

An Isotope (q. v.) that is unstable, disintegrates, and

emits radiations, e.g., uranium-235 which emits alpha and
gamma

rays.

Radiometer

An

instrument that measures the intensity of solar Radia-

tion, cf. Pyrheliometer.

Radiosensitivity

The

sensitivity,

or lack of tolerance of organisms to

endure Ionizing radiation

(q. v.).

Radiosonde

A free balloon with attached instruments and radio transmitter for securing measurement of temperature and atmospheric pressure.

Rainfall

The
hail,

total

amount

of Precipitation including rain, snow,

and other forms.

Rain Forest

type of vegetation consisting of

284

tall,

evergreen

trees,

mostly broadleaved, occurring in equatorial regions with

much rainfall and no, or very short dry seasons.

Rain

Gage

An

instrument to measure the amount of

Shadow

Rain

Refers to an area in which

it

is

rainfall.

or no rain

falls

because

located to the leeward of mountains which

on the

little

opposite side are exposed to moisture-laden winds.

Raised Beach

The

shore of a former lake or sea that has been elevated

movement

by a

of the earth to

form a narrow

plain.

Raised Bog
A Bog with

vegetation of Sphagnum spp. and associated

plants that is typically convex and gently sloping from the
center toward the steep margins, and bordered by a ditch

or a watercourse (lagg).

Ramet
An individual member

of a Clone (q.

v.). cf.

Ortet.

Random Sample

sample of plant or animal life, soil, or other material

or objects in an area in which the sample is located spatially
by chance or at random; in contrast to selected samples or
Systematic sampling (q.

Random

v.).

Searching

The

hypothesis that populations obtain food, suitable

niches, and mates by entirely unorganized search, in contrast
to systematic searching.

Range
(1)

The

extent of the geographic area in which a plant

(2) Land covered with plants that are

or animal occurs.

suitable for grazing; usually extensive in area and not suitable for cultivation, especially in arid, semiarid, or forested

285

regions, cf Pasture. (3)

livestock.
.

A unit of grazing land used by a given

herd of

Range Condition
The

status of vegetation

in relation to the

optimum

and

soil of

a given range area

by some the

status (considered

Climax) obtainable under the prevailing environmental

conditions.

Range,
See

Home

Home

range.

Range Improvement
procedures that are used to increase the value and
ease of management of the range such as the development of
water supplies, fencing, revegetation, and control of unde-

Any

sirable plants.

Range Management
The handling of range land to obtain the continuous production of forage and livestock, consistent with uses of the
land for other important purposes, cf. Proper stocking.

Range Readiness
The

degree of growth of important forage plants on the

and
the condition of the soil so that livestock may
range
without
undue compacting of the soil or decreasing the
graze
capability of the plants to maintain themselves,

cf.

Pre-

mature grazing.

Range Survey

systematic and comprehensive analysis and inventory

of the resources of a range area and the related problems of

management, and the formation of plans

for

management

of

these resources.

Raptorial
Refers to a predatory animal that has feet with curved,
sharp claws adapted for seizing Prey, e.g., eagles.

286

Rasorial
Refers to an animal that usually scratches the ground
for food,

e.g.,

barnyard fowl.

Rassenkreis

series of races in

which

distinct forms of a Polytypic

species replace each other in a geographic progression,

Race

cf.

(1).

Ratoon

A shoot from a perennial plant such as sugarcane.

Raunkider's

Law

of Frequency

See Frequency, law

of.

Raunkider's Life-form Classification

A system of classification

of Life-forms of plants based on

the kinds and position of the organ with respect to the soil
level that survives unfavorable environmental periods, cf.

Phanerophyte, Geophyte.

Rdvine

An

elongated, narrow depression, larger than a gully,

usually formed by running water.

Rdw Humus
See Mor.

Reaction
(1)

The

effects

which one or more organisms produces

Interaction. (2) The degree of acidity or

alkalinity of a substance, usually expressed as
(q. v.). cf.
concentration.
Hydrogen-ion

upon

its

habitat,

cf.

pH

Reaction Time

The time required by an organism for the manifestation

of a response to a stimulus.

Realm
One

of the major divisions in the classification of con-

287

Faunas according to P. J. Darlington,

Megagea (Arctogea), Neogea, Notogea (q. v.).
tinental

Jr.,

e.g.,

Recapitulation

The theory that in the development of an individual

the stages of earlier forms in its evolution are repeated,
in the embryo of a pig. cf. Palingenesis.
e.g., gill slits
Recessive
Refers to a

Gene

that has

no

effect

an organism unless it is Homozygous

nant gene is not present, cf. Allele.

on the appearance
(q. v.),

i.e.,

of

the domi-

Redox-potential
See Oxidation-reduction potential.

Red Tide
See Dino flagellate.

Reduction Division
See Meiosis.

Reed

Swamp

of plants such as cattail or bulrush that

grows in shallow water and often extends landward on wet
soil where the water table is near the surface.

community

Reef

series of rocks close to the surface of a

may be exposed at low

body of water,

tide.

Reflex

An

innate, simple, stereotyped response, located in the

nervous system, occurring very shortly after the stimulus has

been received by an animal.

Reforestation

The
cf.

establishment of a forest on previously cleared land,

Afforestation.

288

Refuge

An

area designated

for

the

within which hunting or fishing

controlled, cf. Natural area.

maintenance of animals
is

prohibited or strictly

Refugium

An area that has not been exposed to great changes undergone by the region as a whole, and as a result provided
conditions suitable for the survival of Relic (q. v.) species,
cf.

Nunatak.

Reg
Parts of the Sahara desert with a gravelly or stony surface
because the fine materials have been blown away.

Regeneration

The

process occurring in some animals by which a part

body which has been lost may be restored, e.g., a
crayfish growing a new appendage, growth of new tissue in

of the

the

wound

of a

mammal.

Regional Climax
See Climatic Climax.

Regionalism

The

concept of the integration of relations in

human

society to the particular conditions and resources that obtain

in a region such as the Columbia River basin or the northern

Great Plains.

Regolith

The unconsolidated mantle of soil material and weathered

rock on the surface of the earth.
Regosol

deep soil consisting of loose material without stones

and shows only slight development of a Profile (q. v.).
289

Regression

statistical method for the study and expression of

(1)
the change in one variable associated with and dependent
upon changes in another related variable or group of vari-

ables. (2) See Retrogression.

Regulatory Mechanism
Any influence in the physical

or biotic environment of a

population that tends to maintain the

number

of individuals

which the resources of the habitat can support,

cf.

Reaction,

Coaction, Predation, Parasitism.

Relative Humidity
See Humidity, relative.

Relev6

An

sample of a Stand of vegetation in which are

given the data on characteristics such as kinds of species,
Cover, Density, and sometimes others, cf. Sample area.
analysis

Relic (Relict)

(1) A remnant or fragment of a flora or fauna that remains from a former period when it was more completely
developed. (2) A remnant of the population of a species that
was formerly more widespread.

Relief

The

inequalities in the elevation of the land surface, cf.

Topography.

Rendzina

An

Intrazonal group of soils usually with brown or

and light gray or pale yellow

black, friable surface horizons

calcareous material below, formed under grassland or mixed

grassland-forest in humid or semiarid regions, cf. Prairie
soil.

Replacement Control
The substitution of one kind

of plant

chiefly as a result of competition, e.g.,

290

by another kind,

downy bromegrass

which is resistant to leafhoppers replacing Russian thistle

and mustards which are susceptible to the insect, cf. Succession.

Reproduction, Vegetative
Propagation of a plant by stems, roots, or other asexual
in number by means
organs, e.g., strawberry plant increasing
Sexual
of runners, cf. Propagate,
reproduction, Asexual
reproduction, Apomixis.

Reproductive Isolation

The

separation of populations or organisms so that interbreeding cannot occur.

Reproductive Potential

The maximum

rate of increase in

numbers of individuals

of a species or a population under the most optimum conditions, in contrast to the actual reproduction obtained under
existing

conditions,

cf.

Biotic

potential,

Environmental

resistance.

Reptile
An animal in the

class Reptilia of the

subphylum Verte-

brata. e.g., snakes, crocodiles.

Roseau
The group of meteorological stations operating under
common direction or in the same territory.

Residual Soil

A kind of soil

formed in place by the disintegration and

of
rocks and the consequent weathering of
decomposition
the mineral materials, cf. Alluvium.

Residual Stand
See Second growth.

Resistance

The
affected

capacity of an organism to remain relatively unby insects, disease-causing bacteria or fungi, or

291

severe conditions in the physical environment because of

inherent qualities that it possesses.

Respiration
The complex series of chemical reactions in all living
organisms by which the energy in foods is made available for
use. In aerobic respiration free oxygen is utilized and carbon
dioxide is liberated; in anaerobic respiration, free oxygen
not required.

is

Respiratory Quotient
The ratio of the volume of carbon dioxide given off by
an organism to the volume of oxygen used in a unit of time.

Restocking

The
trees

is

a forest in which replacement of important

taking place by natural or artificial means, cf.

state in

Reforestation.

Retrogression

The change from

a more highly organized individual,

or
state
of
group,
organization to one on a lower level, as in
a Succession (q. v.) that recedes from the Climax.

Revetment

A structure or obstacles placed along the margins of a

stream in order to protect the bank from erosion.
Rheology
The division

of

Limnology

(q. v).

waters, their physical, chemical,

and interrelationships, cf. Lotic.

and

dealing with running

biological conditions

Rheophyte

plant that grows in running water,

Rheotaxix
The orientation

in

the

cf.

Hydrophyte.

locomotion of organisms in

streams with reference to the current.

292

Rheotropism
The response

of an organism to a current.

Rhesus Factor
See

RH

RH

factor.

Factor
Antigen

An

(q. v.)

found in the blood of a large number

human beings who consequently possess Antibodies against

the antigen. Syn. Rhesus factor.

of

Rhizine

An

organ that serves for the attachment of certain organmany intergrown filaments in many lichens.

isms such as the

Rhizobia
Bacteria that occur in the nodules of certain plants,
especially in the pea family, Leguminosae, and fix free litro-

gen into forms useful

to the Host.

Rhizoid

filamentous organ, one cell thick, found in mosses,

fern Gametophytes, and other plants, used for attachment
and probably also for absorption of water and nutrient salts.

Rhizome

An

underground stem that produces shoots and roots

cf. Rootstock, Runner.

at

the nodes,

Rhizosphere
The portion

of the soil close to

and under the influence

of the root of a plant.

Rhythm
The more
as

or

less

day and night,

regular recurrence of phenomena such

differences in animal behaviour, cf.

Periodicity.

Ridge Terrace

A long,

low ridge with gently sloping sides and a shallow

channel along the upper side for the purpose of collecting
293

run-off water

and diverting the flow

cf. Bench terrace.

across the slope, thus

controlling erosion,

Rift

Valley

A long, narrow valley between two approximately parallel

geological faults, e.g., the extensive one extending from
Lake Nyasa northward in the eastern part of Africa.
Rill

Erosion

The removal

of soil

by running water resulting in the

formation of shallow channels that can be smoothed completely by cultivation in the

sion, Sheet erosion.

normal manner,

cf.

Gully ero-

Rime

feathery or rough layer of ice deposited on plants and

other objects by a fog. cf. Hoarfrost.

Riparian
Refers to land bordering a stream, lake, or tidewater.

Riprap
Stones placed on the face of a dam or on stream banks
or other land surfaces in order to protect them from erosion;
often applied also to other materials that are used for erosion
control.

Riverwash
Barren alluvial land exposed along streams at low water
levels.

RNA
A

(Ribose Nucleic Acid, Ribonucleic Acid)

nucleic acid occurring in the cytoplasm of plant and

animal

cells.

Roaring Forties
Strong westerly winds over the ocean between latitudes
40 S. and 50 S., or the region in which these winds occur.

294

Rock Flour
Fine material formed by the action of a glacier grinding
its base as it moves forward.

rocks in

Rodent

An
e.g.,

animal in the order Rodentia in the

mouse.

class

Mammalia,

Roentgen
(1)

rays

A unit of measurement of radiation caused by Gamma

and

X-rays, very similar to

Rad

(q. v.). (2)

Refers to

X-rays.

Rogue
To remove

undesired individuals from a population to

prevent their reproduction.

Rookery
The breeding

place of a group of birds or seals.

Root Climber

plant that ascends by means of roots attached to a

support, e.g., poison ivy on the trunk of a tree.

Root Nodule
See Nodule.

Rootstock
See Rhizome.

Root Sucker

A sprout arising from a root.

Root Zone
The part

of the soil occupied by roots, or subject to such

under
normal conditions, cf. Rhizosphere.
occupation

Rotation Grazing

The

orderly alternation in the use of two or

tions of a range or pasture.

295

more

por-

Rotifer

An

aquatic animal in the phylum Rotifera, possesses

cles of cilia at the anterior end.

Rouches Moutonnees
Mounds of smoothed

cir-

rock marked by striations caused

by a glacier passing over them.

Roughage
Feed for animals consisting of plants or plant parts conhigh fiber content and low total digestible nutrients,

tains a
e.g.,

hay, Stover.

Rough Grazings
largely on hills and mountains in Great
which have replaced forest by natural processes,
maintained as grassland by grazing, in contrast to pastures
seeded by man.

Grasslands,

Britain,

Roundworm
See Nematode.

Row Crop
A crop such

corn planted in rows relatively far apart,

usually two to four feet, to permit cultivation between the
as

rows.

Ruderal

plant inhabiting fields or waste places,

Exotic.

cf.

Weed,

Rudimentary
Refers to an organism or part of one that
stage of development or evolution.

is

in

an early

Rumen
The

first

stomach of a Ruminant

Ruminant
An animal

(q. v.).

in the order Artiodactyla, even-toed ungulates,

296

class

cud,

Mammalia,
e.g.,

that lacks

upper

incisor teeth

and chews the

giraffe, ox, deer.

Runner

An
roots

above-ground, more or

and shoots

conditions,

e.g.,

at

the

less

horizontal stem that forms

some of the nodes under favorable

strawberry plant,

Bermudagrass.

cf.

Rhizome, Stolon.

Runoff

The
off the

part of Precipitation which as surface run-off flows

soil and the part that

land without sinking into the

ground and passes through into surface streams

groundwater run-off.
enters the

297

as

Sabdlicm Life Zone

The portion of the Austral life zone (q. v.) which borders
the Gulf of Mexico from the southern tip of Florida to the
17th meridian.

Sabulicole

sand-dwelling insect.

Salina

A salt

flat.

Saline Soil

soil that

contains soluble

salts,

usually chlorides

and

sulfates in

high enough concentration so that the growth of

most crop plants is reduced, pH is less than 8.5, often called
"white alkali" because of the presence of a white or gray
crust

on the

surface, cf. Alkali soil, Solonchalk.

Salinity

The

quality of saltness in seawater or fresh water, most

commonly expressed in parts of dissolved salt per 1000 parts

of water,
cf.

e.g., salinity

of seawater

Alkalinity.

298

is

35 parts per thousand.

Salinization

The

formation of a saline

soil

by the addition of

salts

to a non-saline soil, as occurs often in irrigating land with

water of a high degree of Salinity.

Saltation
A sudden change.
Saltatorial (Saltatory)
Refers to leaping or dancing, e.g., the hind limbs of a
kangaroo adapt it to saltatorial motion.

Salt

Grounds

Places in a pasture or

consumption by

on a range where

salt is

placed for

livestock.

Saltigrade
Refers to an animal possessing legs that are adapted for
leaping, e.g. kangaroo rat.

Salt

Marsh
Marsh in which the water

is

salty or brackish,

with

greater Salinity than fresh water.

Salt

Pan
depression in a salt marsh, usually bare of vegetation.

Sample Area

portion of an area of vegetation or of a plot that

used for sampling purposes, cf Plot, Quadrat.

is

Sample Plot

measured area in vegetation used for sampling or an

area of land used for experimentation.

Sample, Random

sample taken without bias from an area or from a

population in which every part of the area or population has
an equal chance of being taken.

299

Sample, Representative

sample taken that is typical of or that represents a

value of the area or population from which it is taken.

fair

Sand Binder

plant that holds sand from being blown away.

Sapling

A tree that is more than three feet in height and

than 4 inches in diameter at breast height.

less

Saprobe

An

organism that

lives

on dead organisms or on decaying

organic material.

Saprophyte

A plant

material,

cf.

that obtains food

from dead or decaying organic

Parasite, Heterophyte.

Sopwood

The outermost part of the wood or xylem of the trunks

of trees, generally lighter in color than the heartwood, contains living cells, active in translocation of water and mineral
nutrients.

Saturation Deficit

The difference between

atmosphere

at a given

the pressure of water vapor in the

maximum that it could

time and the

contain at the same temperature, expressed in millimeters

of mercury; or sometimes expressed as the difference between
the relative humidity

and the humidity

at saturation.

Saturation Point

The density of a given population above which

longer increases.
Saurian
Refers to a lizard.

300

it

no

Savanna (Savannah)
An area of grassland in which are
but

little

scattered trees or shrubs

or no breaks in the continuity of grassland cover.

Saxicolous
Refers to organisms growing on or
many mosses and saxifrages.

among

rocks, e.g.,

Scandent
Climbing.

Scansorial
Refers to an organism that has adaptations for climbing,
a Liana such as Virginia creeper, cf. Ambulatorial,

e.g.,

FossoriaL

Scarp
See Escarpment.

Scatology

The

study of Scats, identification, determination of con-

tents, etc.

Scats
Animal

feces or

droppings such

as pellets of rabbit

dung.

Scavenger

An

animal that eats animal wastes and dead bodies of

animals not killed by

itself, e.g.,

vulture.

Schizomycete

plant in the

phylum Schizomycophyta,

bacteria.

Scion
aerial plant part, often a small branch, that is
onto
the root-bearing part (Stock) of another plant.
grafted

Any

Sciophyllous
See Heliophyllous.

301

Sclerenchyma
Thick walled

cells,

or stone

fibers

cells,

constituting

strengthening tissue in plants.

Sclerophyll
Plants with stiff, leathery, evergreen leaves, may be
broad-leaved as the holly, or narrow-leaved as the pine. cf.

Chaparral.

Sclerosis

The hardening

of tissue

by an increase in the content of

lignin in plants, or an increase in collagen in animals.

Sclerotium

hard, compact, rounded mass of hyphae serving as a

stage for carrying a fungus through an unfavorable

dormant

environmental period;

it

may

survive

many

winters in the

soil.

Scree
See Talus.

Scrub
Densely growing, low, often stunted bushes or
Fruticeta, Bush, Chaparral.

trees, cf.

Searching
See

Random

searching.

Season, Critical

The

part of the year when a species suffers greatest

mortality, e.g., the migration time of some migratory birds.

Seasonal Aspects
See Aspection.

Seaweed
An alga,

usually large, growing in the sea,

e.g.,

kelps.

Sebaceous
Refers to fatty material, particularly to the gland in the
skin of mammals that secretes sebum.

302

Secondary Sexual Character

characteristic, not directly associated with the characters directly connected with reproduction, in which the
male and female animals differ, such as the difference in

coloration of

many male and female

Secondary Species
The species in a community
Dominant

species (q.

white oak

forest.

v.), e.g.,

Secondary Succession
The kind of Succession

birds.

that are subordinate to the

dogwood shrubs or

trees in a

which takes place following the destruction of part or all of the vegetation in an
area, usually caused directly or indirectly by man. cf Primary
succession, Sere, Plagiosere, Sub sere.
(q. v.)

Second-foot

measuring unit for the volume of the flow of water

expressed in cubic feet per second.

Second Growth
(1)

forest

which comes up

after the

removal of the old

stand by cutting, fire, or other cause; actually Young growth.

(2) The smaller trees left after cutting all the merchantable
actually Residual stand,

trees,

cf.

Virgin forest, Advance

growth.

Secretion

The
ticularly

stance

process of passing substances made within a cell, pargland cells, to the outside of the cell; or the sub-

itself, e.g.,

nectar from nectar glands in flowers.

Sedentary
Refers to an animal that has
about,

e.g.,

certain spiders,

little

tendency to move

cf. Sessile.

Sedge

plant, resembling a grass in vegetative appearance, in

303

the family Cyperaceae, with usually solid stems, three-ranked

leaves, and closed leaf sheaths.

Sedimentary Rock
materials such as pebbles, sand, and
clay in rivers, lakes, and seas; usually in distinct layers, e.g.,
conglomerate, sandstone, limestone.

Rock formed from

Sedimentation
The process of

depositing materials from a liquid, espein

of
water,
cf. Sedimentary rock, Alluvium.
bodies
cially

Sediment Delivery Ratio (Percentage)

The relation of the annual Sediment yield
gross

amount

and

annual

of erosion.

Sediment Yield
The total sediment
coarse

to the

outflow from a watershed, includes

fine materials, bedload,

and suspended

materials;

a part of the gross erosion from an area.

Seed
The

reproductive structure in Spermatophytes (flowering

plants and conifers) formed from the Ovule (q. v.), containing an Embryo, seed coat, and, in many kinds of plants, an

Endosperm.

Seed Leaf
See Cotyledon.

Seedling
A young plant produced from a

seed.

Usage in

forest

is still
growing in the nursery, not
in
forest
transplanted. Usage
reproduction; a tree grown
<
from seed and less than three feet in height.

nurseries; a tree

which

Seed Plant

Spermatophyte

(q. v.).

304

Seed Tree

tree purposely left standing at the time of cutting a

purpose of producing seed for reproduction

forest, for the

of trees in the surrounding area.

Seed Year

year in which a given species bears seed in large

numbers.

Seepage
(1) The

water that passes through or emerges from the

ground along a line or surface in contrast to a spring where
the water emerges from a localized spot. (2) The process

by which water

passes through the soil.

Segregation
Separation of the Gene pairs (Alleles) and distribution
of each gene into separate cells during Meiosis (q. v.).

Seiche

An

oscillation in the level of the surface of a lake or

inland sea.

Selection
See Artificial selection, Natural selection.

Selection Pressure

A criterion of the results of Natural selection (q. v.) upon

a population.

Selective Cutting (Felling)

The system of removing certain
ones in a

forest, cf.

trees

such as the largest

Clear cutting.

Selective Grazing

The

habit of grazing animals to eat certain plants in

preference to others, cf. Palatability.

Selective Species
The group of Characteristic species
305

(q.

v.)

in Braun-

Blanquet's scheme of classification that contains species occurring most frequently in only one kind of community, but

may

rarely occur in others also.

Seleniferous
Refers to

soils, plants,

and other substances

that contain

a relatively high concentration of selenium. Some species of

Astragalus are toxic to livestock because of accumulations of

selenium in the

tissues.

Self-fertile
Refers to an organism in which Self-fertilization occurs.

Self-fertilization

The
lized

process by which eggs of an organism can be ferti-

by sperms produced by

itself, cf.

Hermaphrodite,

Self-

sterility.

Self-incompatibility
The condition where pollen of a plant fails to develop
effectively on a Stigma of the same plant, cf. Compatibility,
Self-sterility.

Setting

process of causing Self-pollination.

Self-pollination

The
flowers

transfer of pollen

on the same

plant,

from an Anther
cf.

to the

Stigma in

Cross-pollination.

Self-pruning

The

death and falling of branches, especially the lower

ones, of living trees.

Self-sterility

The
tilized

an egg of an organism to be
by a sperm produced by the same organism,
failure

of

Self-incompatibility.

306

fercf.

Selva

An

equatorial Rain forest in the

Amazon River

basin in

South America.

Sematic
Refers to an organ, odor, color, or other attribute of an
may serve as a warning to other animals.

animal that

Semiarid
Refers to a region or climate that is intermediate between
Arid and Subhumid, with Precipitation-effectiveness ratios
ranging between 16 and 32, and supporting grassland or
shrub types of vegetation.

Seminal
Refers to seed or semen.

Seminatura! Community (Vegetation)

A community in which the development or

character-

have been modified in part by man's influence, e.g.,

a successional community on an area where sagebrush was

istics

burned by man.

Semipermeable
Refers to a

membrane

that permits certain substances

to pass through readily while others pass through slowly or

not at all; differentially permeable.

Senescence

The

process of aging.

Senility

The

state of old age.

Sensory
Refers to the capacity or sense-organ of an animal
by

which

it

receives stimuli.

Sepal
See Calyx.

307

Serai
Refers to Sere

(q. v.).

Serclimax

stage in a Sere before the Climax is reached and remains in that stage indefinitely, e.g., tule marshes in Califor-

Subclimax, Plagioclimax.

nia, cf.

Sere

The

one another in an ecologic

Hydrosere, Xerosere, Subsere, Primary

series of stages that follow

Succession (q.

v.). cf.

succession.

Serology

The

study of the reactions of blood serums to the introduction of foreign substances into the body of organisms.

Serotinal
Refers to the latter part of the

summer

season,

cf.

Aspec-

tion, Estival.

Serotinous
Refers to late opening such as cones of some pine trees
which remain on the trees for several years without opening.

Serpentine

rock or mineral consisting of hydrated magnesium

silicate.

Sessile

An

organism that

place, e.g.,

barnacles,

is

attached to an object or

cf.

is

fixed in

Sedentary.

Seston

The aggregate of substances and organisms that float or

swim in water, including the Bioseston (living organisms)
and the Abioseston (non-living).
308

Settling Basin
The widening or deepening of a stream so that materials
carried in suspension will be deposited.

Sewall Wright Effect

The postulate that if a population is subject to cyclical

fluctuations in abundance, the evolutionary trend of the
influenced by the size (population density and
area inhabited) of the minimum breeding population, cf.
is

species

Natural selection.

Sex Chromosome

Chromosome

(q. v.)

that determines the sex of the

offspring of an organism.

Sex-linkage

The

connection or association of certain Genes or

butes of an organism with the Sex chromosome,

kinds of color blindness.

Sex Ratio
The relationship

of the

numbers

in a population, approximately

such as color,

size,

certain

and females

in most kinds of animals.

Sexual Dimorphism
The condition in which marked
istics

of males

e.g.,

attri-

differences in character-

and form occur between male and

female animals in the same species.

Sexual Reproduction
The production of offspring

resulting from the fusion of

sex cells (Gametes, eggs and sperms), cf. Asexual reproduction, Propagate.

Sexual Selection

A theory to explain certain kinds of evolution based upon

selective

mating such

as the

choosing of a certain mate by a

309

female animal because of attractive features such as the

bright coloration of the male.

Shade Plant

plant that can grow in the shade,

cf.

Heliophyllous.

Shale

An
or

easily splitting

sedimentary rock formed from clay

silt.

Shamal

A
much

wind

that blows with considerable constancy, carrying

dust, in Iraq.

Sheep Month
The amount
by

of forage or feed required for maintenance

its suckling lamb for 30

mature sheep or an ewe and

days, usually figured as equivalent to one-fifth of a

month

Cow

(q. v.).

Sheet Erosion

The

erosion or removal of a rather uniform layer of soil

from the surface of the land by rainfall and Run-off water,
cf.

Gully erosion, Rill erosion.

Shelter

The conditions, objects, or material that provide organisms suitable resting places or protection from attack by
predators or from unfavorable conditions of the physical
environment,

cf.

Covert.

Shelterbelt
A long Windbreak of living trees and shrubs extending
over an area larger than a single farm.

Shingle
More or less rounded pebbles varying
with sand, on seashores.
310

in size, often

mixed

Shinnery
Vegetation consisting of dwarf oaks as dominants, especially in sandy areas in the southern Great Plains.

Shipworm
An animal

of the Lamellibranchiata (clams), especially

Teredo navalis which burrows in submerged wood.

Shock Disease
The deterioration
ganism in which
is abnormal and

in overcrowded populations of an orthe activity of the Endocrine glands (q. v.)

the general condition and viability of the

animals are reduced, which

(crash) in the

number

Shoot
The stem and

result in a rapid decline

of individuals.

may

leaves of a plant taken collectively,

cf.

Sprout.

Shore, Depositing

The

addition of sand,

silt,

rock, to the land adjacent to a

of water or wind.

and

clay,

body

or the removal of

of water

by the action

Short-day Plant

plant that blooms when periods of light are short and

periods of darkness are long, e.g., chrysanthemum, cf.

Photoperiodism.

Short Grass
Grasses that grow only a few inches high, particularly
blue gramagrass and buffalograss. cf. High grass, Medium-

height grass.

Shrub

perennial

woody plant

that differs

low growth and the possession of several

the base.

311

from a

tree

by its
stems arising from

Siblings (Sibs)

The offspring,

brothers and sisters taken collectively, from

the same parents.

Sibljack
Shrub vegetation on deforested land in the Balkan
Peninsula.

Siccation
Processes that include the diminution of rainfall (desiccation) and the drying out of the earth's crust and atmosphere.
(Exsiccation, q. v.)

Siccideserta

Dry

areas such as steppe

and

desert occupied

by open

vegetation.

Siccocolous
See Xerophilous.

Sierozem

Zonal group of soils with brownish gray surface horizons that grade through lighter colored material to a layer
with accumulated calcium carbonate, in arid temperate
climates where vegetation usually is shrubby.

Sierra

chain of mountains with jagged tops.

Sieve Tube

connected end to end, part of the Phloem

tissue in plants, used to conduct food.
tube of

cells

Silage

The
as corn,

partly fermented above-ground parts of crops such

sorghum, legumes, or grasses preserved in a succulent

condition for feeding livestock.

Silt

Mineral particles in the

soil,

312

intermediate between clay

and sand;

mm.

0.5 to 0.002

in diameter according to the

Department of Agriculture system, 0.02 to 0.002 mm.

in diameter according to the International system. (2) In a
U.

S.

general sense waterborne sediment in which the diameters

of individual grains are similar to those of silt (1). (3) Soil
material containing 80 per cent or more of silt (1) and less

than 12 per cent of

clay.

Silting (Siltation)
The deposition of water-borne sediments in bodies of
water, caused usually by a decrease in the velocity of the

water movement.

Silurian

One

of the geological periods in the Paleozoic era, which

began about 360 million years ago and lasted for about 35
million years.

Silva

The

aggregate of the forest trees in an area or country.

Silviculture

The

production and care of forest

trees.

Simian
Refers to monkeys and apes, particularly anthropoid apes;
noun especially for the latter.

or used as a

Simoon
An intensely

hot,

dry wind of Arabian and Saharan

deserts, usually carrying

much

sand.

Sinkhole

A hole

into which water drains

and

passes into

ground channel, occurring usually in limestone

an under-

regions.

Sinter
Deposits, mainly siliceous and calcareous (Travertine),
formed in lakes or springs by evaporation, e.g., terraces of

313

siliceous sinter

around hot springs in Yellowstone National

Park.

Sippe

A plant in the abstract as compared to the concrete plant.

Sirocco

A hot,

south wind, occasionally dust laden, blowing from

the Sahara in the Mediterranean region.

Site

An

area delimited by fairly uniform climatic

conditions, essentially equivalent to Habitat (q.

Site

and

soil

v.).

Index

numerical evaluation of the quality or productivity of

land, especially used in forest land where it is determined
by the rate of growth in height of one or more of the tree
species.

Site Quality

The

capacity of a Site to produce vegetation, particularly

timber or forage.

Skiophyte
See Heliophobous.

Slack

A damp

hollow, or low area,

among sand

dunes.

Slash

The

branches, cull logs, uprooted trees, and other waste

material left on the ground after an area has been logged off.

Slashing

An

area of forest that has been logged off and where the
Slash remains.

Slate

fine-grained, dense rock

by compression,

produced from clay or shale

splitting readily into thin plates.

314

Sleet
or partly frozen raindrops
in the form of particles of clear ice. (2) In British use, snow
(1)

In the United

and rain

States, frozen

falling together.

Slick (Slick Spot)

small area of Alkali or Solonetz (q.

v.) soil.

Slime Mold

An

organism in the phylum Myxomycophyta, characterized in part by a naked, fluid mass of protoplasm that can
move with a flowing motion, cf. Wasting disease.
Slip

The

downhill movement for a short distance of a mass

of wet or saturated

soil.

Slope

The
8.5-16.5

from the hori(5-15%), moderate

inclination of the surface of the land

zontal. Level 0-3.0

(0-5%), gentle 3.0-8.5

(15-30%),

steep 16.5-26.5

(30-50%), very steep

(50-100%), precipitous above 45

26.5-45

(over 100%).

Slough

A wet depression with deep mud.

cf

Swamp, Marsh, Bog.

Sludge
Muddy,

ooze-like sediments in a river bed, tidal

flat,

or

similar location.

Smog
A polluted

atmosphere in which products of combustion

such as hydrocarbons, soot, sulfur compounds, etc., occur in
detrimental concentrations for human beings and other
organisms, especially during foggy weather.

Snow

Density

The

water content of snow expressed as a percentage by

volume. In snow surveys, the ratio of the scale reading
(inches of water) to the length of the core of

315

snow

in inches.

Snowfence

A fence of slats and wire

or other material used to inter-

cept drifting snow.

Snowfield

An

area or mass of

snow

that remains throughout the

summer.

Snowflush

A deposit of soil

material accumulated in a mass of snow

following melting of the snow.

Snow

Line

A line marking

the lower limit of perpetual snow.

Snow-Patch

An

area in which snow melts late in the year and where

Snowflush forms and vegetation is characteristic of such a site

or

is

lacking.

Snow Sample

A core

taken in an accumulation of snow from which the

and
density of the snow may be determined.
depth

Snow Survey

series of measurements of the depth and density of

the accumulation of snow, usually for the purpose of determining the amount of water that is stored in the form of

snow on a drainage

basin, as a

means of forecasting the

later

run-off.

Sociability

The

distribution of organisms in relation to one another

groups within a community. J. Braun-

as individuals or as

five classes of sociability, ranging

isolated individuals to dense masses.

Blanquet recognizes

from

Social Behaviour
The activity of an animal caused by another animal or
316

that influences another animal; the reciprocal interactions

more

of two or

animals.

Dominance
The behaviour pattern

Social

in which one or

dominate other individuals in the group,

cf.

more animals

Peck-dominance.

Social Facilitation.
See Facilitation, social.

Social Hierarchy
See Hierarchy.

Sociation

vegetation type characterized by Dominant species in

the various strata; a subdivision of the Association (4) (q. v.)
in the Scandinavian School of Phytosociology.

Socles
According to F. E. Clements a group of one or more
kinds of subdominant plants in a stage of Succession preceding the Climax, cf. Associes, Society.

Society

group of individuals of one species which

in
their
activities. (2) According to F. E. Clements
cooperate
a group of subdominant plants in Climax vegetation, cf.
Association, Socies.
(1)

social

Sociology

The
istics,

study of the development, composition, characterinteractions of groups of organisms or communiPlant sociology. Ecology.

and

ties, cf.

Sod

A
roots

Sod

surface layer of soil matted or

and rhizomes of

grasses

bound together by

and other herbs,

grasses.

317

especially

by

Sod Grass

A grass

that forms a Sod,

Softwood
The wood
Hardwood

e.g.,

Kentucky bluegrass.

of a coniferous tree,

e.g.,

pine, in contrast to

(q. v.).

Soil

The

aggregate of weathered minerals and decaying

material
that covers the earth in a thin layer in which
organic
plants grow.

Soil

Creep
The very

slow

movement

of surface soil

down

a slope.

Soil Erosion

The

loosening and movement of particles of soil from

the surface of the land by wind or flowing water, including
Accelerated erosion and Normal erosion, cf. Gully erosion,
Rill erosion, Sheet erosion, Splash erosion.

Soil

Horizon

layer of soil with characteristics resulting from soilbuilding processes. See A, B, C horizons, Podzolization.

Soiling

The

as

feeding of livestock with mowed, fresh forage such

bromegrass or legumes, in contrast to their grazing on a

pasture.

Soil Productivity
The capacity of a
of

its

soil to

produce plant growth because

chemical, physical, and biological properties.

Soil Profile

A
all its

vertical section of the soil

from the surface through

horizons into the parent material,

cf.

Soil horizon.

Soil Reaction

The
as

pH

acidity or alkalinity of the soil usually expressed

(q. v.).

318

Soil Structure

The arrangement

of particles in the soil,

e.g.,

single

grain, granular, columnar.

Texture
The relative

Soil

proportions of the various

particles (gravel, sand, silt, clay) in the soil.

sizes of

mineral

cf. Silt.

Soil

Type
An area

is relatively uniform in profile

in texture of the surface soil, a sub-

of soil which

characteristics

and

division of a soil series,

loam are

soil types in

e.g.,

Cecil sandy

loam and Cecil

clay

the Cecil series.

Solar Constant

The

energy received from the sun above the upper limit

of the atmosphere, equal to 1.94 gram-calories per minute

per square centimeter.

Solarizafion

The

inhibiting effect of extremely high light intensities

on Photosynthesis.
Solifluction

The

flow of saturated soil

upon an impermeable

layer

or on frozen ground, especially under conditions of alternate

freezing

and thawing.

Solonchalk

A
salts

type of soil that has a high concentration of soluble

in relation to other soils, usually light-colored, "white

alkali." cf. Saline soil.

Solonetz

type of soil in which the surface horizons of varying

friability are underlain by dark-colored, hard soil which is
usually highly alkaline and columnar in structure, "black
alkali." cf. Alkali soil, Solonchalk.

319

Solonization

The process of soil formation in semiarid and arid

climates where Saline soil (q. v.) or Solonetz is formed, cf.
Podzolization, Calcification.

Solstice

The
which

is

time of the year when the sun is above the point

farthest north or south of the equator, in the

northern hemisphere the

summer

the winter solstice about

December

Solum
The upper part

solstice is

about June 21,

22.

of the Soil profile (q. v.) above the parent

material, usually the A and B horizons; often considered the

true soil because of its development by soil-building forces.
cf. Soil.

Soma
The cells of an organism exclusive of those concerned
with Sexual reproduction.
Somatic
Refers to the Soma, or the non-reproductive parts of an

organism.

Sonoran Life Zone

The part of the Austral

life

zone

(q. v.) lying

west of the

100th meridian, divided into Transition, Upper Sonoran,

and Lower Sonoran zones.

Spat

juvenile form of a bivalve mollusk such as the oyster.

Spawn
(1) The eggs of frogs, fishes, oysters and other aquatic
animals. (2) The Mycelium (q. v.) of certain fungi especially
of the mushroom in which it is used for propagation.

Spay
To remove

the ovaries from a female animal.

320

Specialized
Refers to an organism, or part thereof, that is adapted to
a particular kind of life or to a certain combination of
environmental conditions; more limited than an unspecialized organism.

Speciation

The
formed,

processes in evolution
cf.

by which new

species are

Mutation, Natural selection. Sub spe elation.

Species

unit of classification of plants and animals, consisting

and most inclusive array of sexually reproducand
ing
cross-fertilizing individuals which share a common
gene pool; the most inclusive Mendelian population (q. v.),
of the largest

the white pine (Pinus strobus) and ponderosa pine

(Pinus ponderosa) are two species in the genus Pinus. cf.
e.g.,

Jordanon,

Ecospecies,

Coenospecies,

Taxon, Syngameon,

Superspecies.

Species-area Curve

graph showing the number of species on the vertical

axis and the area of the sampling-unit or Quadrat on the
horizontal axis; used to determine the most suitable area
of quadrat to use in sampling vegetation.

Specific Gravity (Soils)

The ratio of the weight of a given volume of soil, pore
space excluded, to the weight of an equal volume of water;
the average specific gravity of tilled surface soil is about 2.65.
Specificity

The

limitation of an organism to restricted, definite set

of environmental conditions, a single kind of food plant or

animal host, or other set of circumstances.

Spectrum, Biological
See Biological spectrum.
321

Speleology

The

study of the conditions and the

life

in caves.

Sperm

The male

sex cell or Gamete.

Spermatogenesis
The formation of sperms

Spermatophytes
The seed-bearing

in

an organism.

plants, Spermatophyta, a section of the

subphylum Pteropsida, phylum Tracheophyta.

the Gymnosperms and the Angiosperms (q. v.).

It includes

Spermatozoon

A highly motile Sperm occurring in animals.

Sphagniherbosa
Plant communities with abundance of

with peat in the substratum,

cf.

Sphagnum and

Bog.

Sphagnum

genus similar to the true mosses, in the subclass

Sphagnobrya, class Musci, phylum Bryophyta; usually occurring in bogs.

Sphagnum Bog

kind of community characterized by the presence, and

often the abundance, of Sphagnum, acid substrata, and the
accumulation of peat. cf. Bog.

Spikelet

One of the main parts of the inflorescence of a grass or

a sedge, containing one or more flowers (Florets) and associated bracts or scales.
Spillway

A passageway for the escape of excess water around a dam.

Spinney (Spinny)

A copse

or small grove.

322

Spiracle

One
most

of the external openings of the Trachea (q.

terrestrial

v.)

of

Arthropods.

Spirochete (Spirochaete)

microorganism which moves by undulating its body

(not by cilia), parasitic or free-living, classified usually with
the bacteria, e.g., the organism causing syphilis.

Spit

long,

narrow

strip of

land extending into the

sea,

attached to the mainland at one end.

Splash erosion

The
ground

direct effect of the impact of rain drops on the

surface or on a thin film of water causing detachment

which are then readily available

of soil particles

away.

cf.

for

washing

Erosion, Sheet erosion, gully erosion.

Sponge
An animal

in the

phylum

Porifera.

Spontaneous Generation
The belief that organisms, even

complicated ones, orig-

inated directly from non-living substances,

cf.

Biogenesis.

Sporangium

structure

case-like

in

plants

in

which spores are

produced.

Spore

An

tive

Haploid (q. v.), one- or few-celled, reproducbody produced by organisms, cf. Spore-mother cell.
asexual,

Spore-mother

Diploid

Haploid

Cell

(q. v.) cell in plants that gives rise to

four

spores.

Sporophyll

or

leaf or leaf-like structure or scale that

more Sporangia^

e.g., leaves of

323

many

ferns,

produces one
a Stamen.

Sporophyte
The part,
plants in

or asexual generation, of the life cycle of

cells contain the Diploid (or Polyploid)

which the

number

of chromosomes, begins with Fertilization, produces Spores, e.g., a flowering plant, a fern.

Sport

A vegetative or Somatic Mutation

e.g.,

(q. v.) in an organism,

a shoot differing from other shoots arising from a bud

on a

plant.

Speculation

The

rapid formation of Spores by fission as in

bacteria, molds, algae, and protozoons.

Spread
The combined
ment
cf.

results of dispersal

of the individual

and then the

and of the

species in a

many

establish-

new

place,

Dispersal, Establishment.

Sprigging

The

planting of a part of the stem and root system of

a grass.

Spring Overturn

The mixing

of water in lakes after the ice melts, result-

uniform temperature from the surface to the bottom.

Another mixing occurs in the autumn, the Fall overturn.
ing in a

Springtail
See Collembolon.

Spring

Wood

The

portion of the annual woody growth of a tree or

is formed in the early
part of the growing
it
is
more
than
Summer
the
wood (q. v.).
season;
porous
a shrub that

Sprout
The

first

growth or shoot from a

seed, root, or other plant

part; or a tree that has grown from a stump or root.

324

Square-foot Method
A method used to determine

the species composition and

the cover of range vegetation by means of systematically
located sample areas one square foot in area.

Stabilization

The

(1)

state in the interrelationships of

organisms in

which integration and adjustment between the organisms

and between them and the prevailing environment is being
attained, maximum stabilization occurs in climax communities usually. (2) In oceanography the condition in a
mass of water in which a density gradient has become established such as when a Thermocline occurs.

Stamen
The

part of a flower that produces pollen, consisting of

an Anther (contains the pollen) and a filament (the

stalk).

Staminate
Refers to a flower that bears stamens.

Stand

A
or

less

general term for an aggregation of plants with more

uniformity in Physiognomy, composition, and habitat

conditions; a local example of a

tion (q. v.).

Community-type or Associa-

Standing Crop
The total amount of the Biomass (q. v.) of organisms of
one or more species within an area. cf. Productivity, Yield.
Standort

The

influence in the aggregate of all factors (climatic,

edaphic, biotic, orographic) upon a geographically delimited
locality, cf. Habitat.

Stand Table

A listing

of species that occur in a stand, including data

325

on
cf.

characteristics such as Cover,

Vitality,

and Frequency.

Association table.

Station

A particular location
or a locality,

cf.

comprising a stand, part of a stand,

Habitat, Standort.

Steady State
See Homeostasis.

Stele

The central part of the stem or root of plants, includes

the pericycle, Phloem, Xylem, and pith when present.
Steno-

A prefix denoting a narrow range of Ecological amplitude

an organism,

(q. v.) of

e.g.,

stenothermal refers to tempera-

stenophagous to variety in the diet, stenoky to number

of factors, stenohaline to salinity, stenohydric to water, cf.
ture,

Euroky.

Steppe

An extensive area of natural, dry grassland; usually used

in reference to grasslands in southwestern Asia and southeastern Europe, cf. Prairie, Pampas.

Stereotaxis
See Thigmotaxis.

Stereotropisiii

The growth
an

of a plant organ in response to contact with

around a stem.

object, e.g., tendrils of vines coiling

Sterility

The

lack of ability of an organism to carry

on Sexual

reproduction.

Stigma
The upper
the pollen

and

part of the pistil (carpel) of a flower, receives

aids in its germination, cf. Pollination.

326

Stilling Basin
An excavation or structure below a waterfall or rapids
that reduces the velocity and turbulence of the current.

Stimulus

An

influence that causes a response in an organism or

in a part of

it.

Stock
and

The

parts of a plant, usually a portion of the stem

the root system, to which a Scion is grafted. (2) Live-

(1)

stock. (3) See

Standing crop.

Stocking
Placing animals such as deer or domestic livestock on

an area of vegetation.

Stolon

on the surface

ground where it
propagates vegetatively by forming new Shoots and roots at
the nodes, e.g., Bermuda grass, cf. Runner, Rhizome.
horizontal stem

of the

Stoma (Stomate)

A minute pore and two surrounding guard cells occurring

in the epidermis of leaves, young stems and fruits,

organs, through which diffusion of gases occurs.

and other

Stool

The base of a plant from which shoots arise, or the base

including the shoots, cf. Tiller.
Stover

The

dry, cured stems and leaves of grain crops such as

corn and sorghum after the removal of the grain, cf. Fodder,

Forage, Feed.

Strain
A group of organisms having distinctive attributes and a
common lineage which differs from other groups, but which
is not sufficiently distinct to form a breed or Variety.
327

Strand
(1)

which

The
is

area of bare beach above the level of high water,

subject to the action of wind. (2) The intertidal

portion of a beach.

Stratification
See Layering, Thermal

stratification.

Stratified Sampling
In sampling vegetation or a geographic complex the
separation into types or blocks in order to secure the maxi-

mum degree of Homogeneity

in the area to be sampled.

Stratosphere

The upper

region of the atmosphere beginning about

six miles above the surface of the earth, in which water-vapor
clouds do not form and where no marked changes in temperature take place as the altitude increases.

Stratum
See Layer.

Stream

general term for water flowing in one direction such

as a rill, rivulet, brook, creek, and river.

Streptomycin

An Antibiotic (q. v.)

produced by the mold, Streptomyces

griseus.

Stress
(1) Systemic. According to Selge the condition of an
animal in which large parts of the body deviate from their

normal resting state, either because of their activity or

because of an injury. (2) The total energy with which water
is

held in the

soil.

Stressor

A stimulus causing systemic stress.

328

Stridulation

The making
crickets

by certain insects such

one
by rubbing
organ against another.
of shrill sounds

as

Cropping
The growing of

Strip

crops in narrow fields or strips so that

wind and water erosion is reduced or prevented, cf. Buffer
strips.

Survey
The use of

Strip

continuous narrow

strips as

sampling units,

especially in forestry.

Strobilus (Strobile)

cluster of Sporophylls; the cone of conifers in

seeds or pollen grains are produced.

which

Structure
(1)

ing,

An

expression of the composition, abundance, spacattributes of plants in a community, cf.

and other

Layering, Life-form. (2) The composition of a population

with reference to age-classes, or to some other criterion. (3)

See Soil structure.

Struggle for Existence

Refers to the processes used by an organism to maintain
life and to reproduce, especially in an unfavorable environ-

ment or where Competition

(q. v.)

is

severe, cf.

Natural

selection.

Stubble

The lower parts of plants that remain after the tops have
been removed in harvesting operations; may also be applied
to the parts left ungrazed

on range or

Stubble Crop
(1)

pasture.

A crop that is produced from Stubble of the previous

A crop sowed in the grain Stubble after the grain

season. (2)

329

crop such as wheat has been harvested; for the purpose of

plowing it under the following spring to increase organic
matter in the soil.

Stubble Mulch

The

residues of a crop left

to prevent or reduce erosion

on the

soil surface as

when preparing

a mulch

the land for

planting another crop.

Stumpage
The

it

stands in a forest; the uncut

pistil

between the stigma and the

value of timber as

timber.

Style

The

portion of the
ovary in a flower.

Subalpine
Refers to the region or zone in mountains below the
treeless

Alpine

by coniferous

(q. v.) region, characterized in

forests, especially

spruce and

North America

fir.

Subarctic
Refers to the region south of the Arctic (q. v.) region
and includes the northern part of the region south of the
geographical timber line. (2) Boreal.
(1)

Sub-boreal Period

The

from about 2500 B. C. to about

700 B. C. according to Blytt and Sernander, a period drier
than the preceding Atlantic (5500-2500 B. C.) and the followclimatic period

ing Subatlantic (700 B.C. to the present) periods,

cf.

Boreal

period.

Subclimax

A
ment

subfinal stage in Succession in which further developis inhibited because of the influence of some factor

other than the climatic factors,

330

cf.

Proclimax, Serclimax.

Subdominant

species in a

nance

(q. v.)

community

that exerts

much

less

Domi-

than the Dominant species.

Suberin
The waxy

material found in walls of chiefly cork cells

in plants.

Suberization

The

process of Suberin formation in plants.

Subhumid
Refers to climatic regions where the moisture conditions
range from 20 inches in the cool parts to 60 inches in the

hot parts; and where the natural vegetation consists chiefly

of tall grasses, and where many kinds of crops can be grown

without irrigation, or dry farming procedures.

Subinfluent

An

organism that has

community and

is

less effect

than an Influent in a

present usually for only a part of the year.

Subirrigotion

The

control of the water table so as to raise

it

near or

into the root zone.

Sublittoral
The lower division, at a depth from about 40 or 60
meters to about 200 meters in the sea, of the Neritic or Benthic zone, below the Littoral division. These terms apply
also in a general

way

to lakes.

Subpolar Region
Approximately the region south of the Tundra, occupied

by Boreal

forest.

Subsequent Reproduction
Trees which have grown up in openings in the forest
331

or under the canopy following cutting or after regeneration

operations have been started.

Subsere
See Secondary succession.

Subsoil
Approximately the B horizon in soils that have distinct
profiles; where the profile development is weak the subsoil
is below the plowed soil, or its
equivalent, in which roots
normally grow, a vague term.

Subsoiling
Tillage of the Subsoil (q. v.) or the soil below the normal
depth of plowing, cf. Chiseling.

Subspeciation

The

formation within a species of populations that differ

consistently one from another in Genotypic constitution and
in the resulting Phenotypes. Isolation of such Subspecies
may in time give rise to new Species, cf. Speciation.

Subspecies
A Taxon

of distinct, geographically separated complexes

of genes, immediately below Species and above Variety (if
varieties are recognized in a species), sometimes considered

as

synonymous with

variety, or as

an incipient

species.

Substitute Species
See Vicariation.

Substratum
(1) The base,
growing.

(2)

or substance upon which an organism

term for the C horizon (q. v.).

is

A vague

Subtropical
Refers to the region between the Tropics and the Temperate zone, with distinct summer and winter seasons and
with greater heat than the Temperate zone.

332

Succession (Ecological)

The

replacement of one kind of Community by another

kind; the progressive changes in vegetation and in animal
life which may culminate in the Climax (q. v.). cf. Allogenic,
Autogenic, Primary succession, Secondary succession, Sere.

Succulence

The

condition of a plant that contains

and is therefore fleshy or juicy, e.

in cell sap

much

tissue rich

g., cactus.

Sucker
(1)

In some animals an organ of attachment and also

often used for the absorption of food. (2) See Haustorium.

(3) In many plants a shoot arising from the lower parts of

the stem or from the root.

cf.

Tiller, Sprout.

Sudd
An

extensive Marsh type of vegetation characterized by

Dominance of papyrus (Cyperus papyrus) along the
upper White Nile River, large masses of which may break
loose and float down the river.
the

Suffrutescent
Refers to Perennial plants that normally are somewhat
woody at the base so they do not die down to the ground

each year.

Suffruticose
Refers to Perennial plants that are distinctly woody at
the base, herbaceous above (Undershrubs), intermediate to
Suffrutescent and Fruticose (q. v.).

Sulfofication

The

Mineralization

(q.

v.)

of organic

compounds

in

dead remains of plants and animals to inorganic compounds

containing sulfur such as calcium sulfate which can again
be absorbed by plants.
333

Summation Temperature
See Temperature summation.

Summer Fallow
The

which crops have not been

control weeds and to accumulate soil

cultivation of a field in

planted in order to
moisture for the growth of a crop subsequently,

cf.

Fallow.

Summer Wood
The less porous and harder portion of the Xylem (q. v.)
of a growth layer in woody plants produced in the latter part
of the growing season, cf. Spring wood.

Sun Plant

A plant that grows well in full sunlight, cf. Heliophyllous.

Sunscald
Death of tissues of a plant caused by high temperature
and loss of water in organs exposed to bright sunshine.

Sunspot Cycle
The alternation
spots
spots;

in occurrence of a period of numerous

the surface of the sun and a period with fewer

on
one

cycle averages

about

11 years.

Super-organism
See Epiorganism.

Superparasite

A secondary Parasite,

i.

e.,

a parasite using another as

its

Host.

Supersonic
Refers to vibrations exceeding 20,000 per second, not

audible to the

human

ear.

Superspecies

group of related Species that are geographically isowithout any implication of natural Hybridization
among them. cf. Syngameon.

lated;

334

Supralittoral (Zone)

The

portion of the shore immediately adjacent to the

tidal zone.

Supraneuston
Collectively, the

minute organisms associated with the

upper surface of the film of water in

lakes, streams, ^etc. e. g.,

the water-strider.

Supraorganism
See Epiorganism.

Surface Run-off
See Run-off.

Surface Soil

The upper

part of cultivated soil, usually stirred during

tillage operations, or the equivalent depth of 5 to 8 inches
in non-cultivated soils.

Surplus Stock

The

portion of the population of

game animals or fish

number needed

at the time of harvest that are in excess of the

to maintain

an adequate breeding

Survival Potential
The capacity of an organism

stock.

to survive in a given en-

vironment.

Swale
An arei of low, wet land;

Swamp
A land

a low meadow.

area containing excessive water

much

of the

year and covered with dense, native vegetation that includes

trees; but the term is used with various meanings, cf. Marsh,

Bog.

Sward
An area
grasses, cf.

of grassland, especially one composed of sod-

Turf.

335

Sworm
A dense

aggregation of minute aquatic organisms, or of

certain insects such as bees

and midges.

Sweep-net Method

A technique for determining an evaluation of the density

and other invertebrates

an area by making a
certain number of swings of a standard entomological sweep
of insects

in

net.

Sweepstakes Bridge
The accidental transportation
rier

from one area

tion occurs,

e. g.,

of organisms across a bar-

where no land connecthe migration of a few kinds of animals

to another, usually

from Africa to Madagascar,

cf.

Filter bridge, Corridor.

Symbiont
In a broad sense an organism that
tion with another, cf. Symbiosis.

lives in close associa-

Symbiosis
In a broad sense the living together of two or more organisms of different species; including Parasitism, Mutualism, and Commensalism (q. v.). cf. Coaction. In a narrow
sense synonymous with mutualism.

Symmetry
The

condition of similarity in form or structure in the

of
an organism on each side of an axis dividing it.
parts
cf. Bilateral symmetry,
Zygomorphy.

Sympatric
Refers to the origin or area of occupation of two or more
closely related species in the same geographical area. cf.
Allopatric.

Synapse
One of

the places in the nervous system of animals where

336

nerves touch one another and where stimuli are transmitted

from one nerve

cell to

another.

Synopsis

The

pairing of Homologous chromosomes (q.

of
Meiosis (q. v.).
stages

v.)

in early

Synchorology
The branch of

Plant sociology dealing with the occurrence and distribution of communities, cf. Plant geography.

Syncline

geological structure or fold

posite sides dipping

Anticline.

formed by

strata

downward toward a common

from opline. cf.

Synconium

kind of fleshy fruit in which the seeds are produced

surface of the concave or hollow receptacle,

on the inner
e. g., fig.

Syncytium
In certain animals a mass of cytoplasm containing many
nuclei within a single plasma membrane, cf. Coenocyte,

Plasmodium.

Syndactylism

The

condition in which two or more digits are at least

partly joined.

Synecology
The study
ties,

of the environmental relations of communia branch of Plant sociology.

Synergism
The total
producing an

activity of separate agents such as various drugs

effect which may be greater than the sum of

the effects of the individual agents.

337

Syngameon
The sum

total of species linked

by frequent or occasional

Hybridization in nature; a hybridizing group of species; the

most inclusive interbreeding population.

Syngamy
The

fusion of Gametes; the Fertilization of an egg* by a

sperm.

Syngenetics

The branch

of Plant sociology dealing with the origin

and development of communities,

cf.

Succession,

Community

dynamics.

Synthesis Table
See Association table.

Synusia

An

aggregation of plants belonging to the same Life-form

having similar environmental requirements and occurring

in a similar Habitat, e. g., a layer of moss plants, a
of floating herbs such as water lilies.

group

Systematic Plant Sociology

The branch

of Plant sociology that deals with the de-

and description of communities, followed by

them
into categories such as Sociation, Association,
grouping
Alliance, Order, and Class.
limitation

Systematic Sampling
A method of sampling in which the samples are
tributed in a regular manner so that the sampling units
be located as uniformly

as possible over the area

dis-

will

under

study.

Systematics

The

science of classification; including the description,

naming, and grouping of organisms in categories such as

338

species, genus, family, order, and class; with especial consideration of evolutionary relationships.

Systemic
Refers to the entire body of an organism, e. g., the whole
body of an organism being affected by a disease.

339

Tableland

A
or

broad, elevated area of land

cliffs, cf.

bounded by

steep slopes

Mesa.

Taiga

The open
Tundra

forest, usually coniferous,

(q. v.) cf.

adjacent to the arctic

Boreal Forest.

Tailings
Accumulations of coarse rock debris from which the finer
materials have been removed during mining operations.

Tallgrass Prairie
See True prairie.

Talus
Accumulations of rock fragments below steep slopes or
caused by the effect of gravity.

cliffs,

Tame
An

Pasture
area of land once cultivated

plants, used for grazing,

cf.

and seeded

Range, Ley.
340

to cultivated

Tank, Earth

made by an

structure

excavation and an earthen

across a drainage course for the purpose of

drinking water for livestock.

dam

impounding

Tapeworm

flatworm in

class Cestoda, phylum Platyhelminthes,

adult
in
the
stage in the intestines of Vertebrates.
parasitic

Taproot System

root system in plants characterized by a large primary

root (the taproot) that extends deep into the soil and has
many smaller branches, e. g. alfalfa, cf. Fibrous root system.

Tarn

small lake or pool in the mountains.

Taungya
An area

cleared of vegetation and undergoing Secondary

Succession in Burma.

Taxis
Movement
a stimulus,

of an organism directly towards or

e. g.

Phototaxis, (q.

away from

v.)

Taxocline

series of gradations in

in which hybridization

is

taxonomic

status of organisms

involved.

Taxon
Any taxonomic

category,

e. g., species,

genus, variety.

Taxonomy
The
ment

science of classification of organisms; the arrangeof organisms into systematic groupings such as Species,

Genus, Family, and Order,

cf.

Systematics.

Tectonic
Refers to processes that cause the formation of features
of the earth's crust, e. g., upwarping. cf. Isostasy.

341

Teleology

The
wards

belief that the processes of nature are directed tosome end or goal such as plants store starch for the

purpose of surviving.

Telotaxis

The

direct orientation of an organism to the gradient of

known only in response to light, cf. Taxis, Tropo-

a stimulus,
taxis.

Temperate Zone
The portions of

the earth in the northern and southern

between
the Tropics (q. v.) and the polar circles
hemispheres
2327' from the poles, cf. Frigid zone.

Temperature
See

10

Coefficient

Temperature, Effective
The temperature above

a certain

minimum,

at

which

physiological processes such as growth of an organism are

active, considered
(41 F.) for many plants.

5C

Temperature Inversion
See Inversion, temperature.

Temperatures, Cardinal
The minimum, optimum, and maximum temperatures
for the

growth of an organism or organ, or for a process or

activity.

Temperature Summation
The summing of effective

temperatures or Day-degrees

(q. v.) for a period of time or for the length of time required
for the development of an organism or organ. See Aliquote.

Temperature Zero
The temperature below which

number

of physiological

processes of an organism cease or are carried

slow

rate. cf.

Temperature,

effective.

342

on

at a very

Temporary Pasture

pasture used for grazing for only a short period, usually composed of annual plants, cf. Tame pasture.

Tendon

A band of dense, fibrous tissue connecting a muscle

some other part, usually a bone, in an animal.

to

Tendril

or stipule of a plant, modified into

a slender structure that coils around an object thus giving
stem, leaf,

leaflet,

support to the plant bearing the tendril,

e.

g.,

pea vines,

clematis.

Tensiometer

An

instrument for measuring the tension with which

water is held in the soil. cf. Stress.

Tentacle

slender, flexible organ, usually tactile, attached to the

head of many kinds of animals such

snails; also the hair-like structures

dew

as insects, jellyfish,

on the

and

insectivorous sun-

plant which traps insects.

Teratology

The

study that deals with monstrosities and malforma-

tions in organisms, especially in

Termitarium
A mound constructed and

man.

inhabited by termites.

Termites
Animals in the order Isoptera (white ants), resembling
true ants, forming large, complex colonies with a highly developed social system, occurring especially in the Tropics.

TermiticoSe

An

organism inhabiting a termite

nest.

Termitiphile

An

organism living with termites in their

343

galleries.

Terrace
Flat or undulating land usually with a steep face
bordering a stream, lake, or sea cf. Floodplain. (2) An em(1)

bankment of earth

built across a slope to control Run-off

and

reduce erosion.

Terrestrial
Refers to the land.

Terrigenous
Refers to deposits derived from the land.
nous, Autochthonous.

cf.

Allochtho-

Terriherbosa
Herbaceous types of vegetation on dry land,

e. g.,

Steppe,

Prairie.

Territoriality
The behaviour of an animal when
intruders,

e. g.,

various birds and

it

defends an area from

fishes.

Territory

The

area occupied by an individual or group of organisms. (2) The area which an animal defends against in(1)

truders,

cf.

Home

range.

Terron

An

earthen construction

made

of bricks that have been

cut directly from the natural sod of sedge

in the sun. cf. Adobe.

meadows and dried

Tertiary

The

of two geological periods in the Cenozoic era

comprising the Paleocene, Eocene, Oligocene, Miocene, and
Pliocene epochs; in order from the oldest to the most recent.
first

Testa

The

outer covering or coat of seeds.

344

Tetraplotd

An organism or part of one having four sets of chromosomes in its nuclei, cf. Haploid, Diploid, Polyploid.

Texture (Soil)
The property

of the composition of soil that deals with

the relative proportions of various sizes of separates or mineral particles including clay, silt, sand, and gravel, cf. Structure.

Thai lop hyte

plant in any one of the phyla of algae and fungi, formerly classified in the division Thallophyta.

Thallus

A
and

plant body that

is

not differentiated into leaves, stems,

roots; one- to many-celled, e.

Thermal Constants
The sum of Day-degrees

g.,

Thallophytes.

(q. v.) of

temperature that

quired fqr a plant to mature after planting,

cf.

is

re-

Temperature

summation.

Thermal Stratification
The condition of a body

of water in which the successive

horizontal layers have different temperatures, each layer

more or less sharply differentiated from the adjacent ones,
the warmest at the top. cf. Epilimnion, Hypolimnion, Inverse stratification, Thermocline.

Thermal Zone

(Belt)

A well defined area or zone, occurring on some mountainwhich the vegetation

in the spring and fall.

sides, in

is

exceptionally free from frost

Thermocline

The
which

layer in a thermally stratified body of water within

the temperature decreases rapidly with increasing

345

depth usually
cf.

Thermal

at a rate greater

than

C. per meter of depth,

stratification.

Thermodynamics, Laws of
(1)

Energy and work are transformable from one to an-

other kind, e. g., sunlight to chemical energy. (2) Spontaneous transformation of energy is accompanied by dispersal of a part into non-available heat such as in respiration.
(3) The absolute zero temperature is not attainable.

Thermogenic
The production

of heat as occurs in an organism during

respiration.

Thermogram
The

continuous

record

of

temperature

made by

Thermograph.

Thermograph

A self-recording

thermometer.

Thermonasty
The response
in temperature,
ture rises.

of an organism to a general diffuse change

e.g., the opening of flowers as the tempera-

Thermoperiodism
The effects of the

alternation of temperature such as

occurs during day and night alternations

upon organisms.

Thermophilous
Refers to organism that grows well in high temperatures, e.g., bacteria in hot springs.

Thermotaxis
The movement

of an organism toward heat or cold as a

stimulus.

346

Therophyte
One of the

classes of life-forms of

Raunkiaer that includes

the annual plants.

Thiamine

vitamin (Bj) required by numerous organisms, but

formed only in green plants and in some microorganisms.

Thicket
Vegetation that
trees

is

dominated by a dense growth of small

and shrubs.

Thigmotaxis
The movement

of an organism to secure close contact

with an object, syn. Stereotaxis.

Thigmotropism
The response

of a plant or a portion of it to a contact stimulus, e.g., a tendril growing around a stem. syn.

Stereotropism.

Thorax
(1) The

part of the body in higher Vertebrates, containheart

and lungs. (2) The middle portion of the body
the
ing
of insects, bearing the legs and wings (when present).

Thorn

stiff,

pointed, modified branch in plants such as the

hawthorn.

Thorn Forest

A vegetation

type in the Tropics or Sub tropics consisting

of
thorny trees, shrubs, and vines; Xerophytic in
mostly
and
subject to long droughts.
aspect,

Threadworm
See Nematode.

347

Threshold

The
to

duration or intensity of a stimulus that

produce response in

is

required

an organism.

Thrombosis
The coagulation

or clotting, as of blood, in the vascular

and lymphatic systems of living animals.

Thyroid
One of
secretes a

the Endocrine glands (q. v.) found in Vertebrates,

containing iodine.

Hormone

Thyroxine
The substance

containing iodine produced by the Thy-

roid gland.

Tick

An

animal in the order Acarina,

sucks blood,

the fever tick

e.g.,

on

Arachnida, which
Also used for some

class

cattle.

parasitic dipterous insects such as the sheep tick.

Tidal Flat

An

flat, muddy area, periodithe lower parts daily, the higher parts

essentially barren, nearly

cally covered by

tides,

only during exceptionally high

Marsh

Tidal

tides.

low

flat

marshland that

tidal sloughs, usually

is

intersected

by channels and

covered by high tides, with vegetation

and other low, salt-tolerant

consisting of rushes, grasses,

plants.

Tidal

Zone

The

area of a shore between the levels of high and low

zone.

tides, syn. Intertidal

Till

An

unstratified deposit of gravel, boulders, sand, and

which has been transported by a glacier, cf.

finer materials

Drift, Colluvium.

548

Tillage

The

operations such as plowing, harrowing, and disking

that are used in cultivating the soil in order to make conditions more suitable for the growth of crop plants.

Tiller

A Shoot

arising

from the base of a plant

as in

wheat and

other grasses.
Till

Plain
more or

less level

land area covered with glacial

Till.

Tilth, Soil

The

physical condition, particularly Structure, of soil with

reference to favorableness for growth of crops; characterized
by friability, high degree of non-capillary porosity, and stable

granular structure. Soil in poor

tilth

is

non-friable, hard,

non-aggregated, and difficult to cultivate properly.

Timberline
in

This term usually denotes the upper limit of tree growth

mountains or poleward in latitude, cf. Tree limit.

Tissue

organized, usually compact group of cells that have

similar structure and function, e.g., cork tissue in plants,
bone tissue in animals.

Tissue Culture
The growth in a suitable medium of a portion of
separated from a plant or animal body.

tissue

Tolerance

The capacity of an organism to live under a given set

of conditions within its range of Ecological amplitude (q. v.),
between the Maximum and the Minimum (q. v.) (the limits
of tolerance),

cf.

Preferendum.

Topography

general term to include characteristics of the ground

349

surface such as plains, hills, and mountains; degree of Relief,

steepness of slopes; and other physiographic features.

Topsoil

The uppermost

portion of the soil, often considered the

layer six or seven inches in thickness, which is richer in
organic material and lighter in texture than the material

below. In uniform material the topsoil includes the layer

that

is

usually plowed up.

cf.

Subsoil.

Tornado

violent vortex, with a diameter usually of about

(1)
0.25 mile, in the atmosphere, accompanied by a pendulous,
more or less funnel-shaped cloud. (2) In West Africa a
violent thundersquall.

Torrential
Refers to the rapid and violent movement of materials
such as water in a stream, heavy rainfall, sliding of gravel,
etc.; or to organisms living in swift streams.

Torrid

Zone

See Tropics.

Total Digestible Nutrients

(T. D. N.)
standard evaluation of the digestibility of materials
in the feed of livestock, including proteins, fats, nitrogen-

The

free extract,

and

fiber content.

Total Estimate
The combined estimates of abundance and cover characteristics of vegetation;

used commonly in England.

Toxin

poison produced by an organism.

Trace Element
See Essential element.

350

Tracer

Radioisotope isotope (q. v.) used to follow the course

of or to determine the location of a normal element in an
organism.

Trachea
(1)

Vessel in the

Xylem

The tube
One of the

(q. v.) in plants. (2)

from the throat

to the lungs in Vertebrates. (3)

small tubes that conduct air in the bodies of most Ar-

thropods,

especially

through Spiracles

in

insects,

opening to the exterior

(q. v.).

Tracheid

long,

thick-walled

cell,

without perforations, with

tapering ends, that conducts water and gives support, located

in the Xylem of plants, especially Conifers.

Tracheophyte
A member of

the Tracheophyta (vascular plants) com-

most primitive),
Lycopsida (the clubmosses), Sphenopsida (the horsetails), and
the Pteropsida (the ferns, conifers and their allies, and the
prising four subphyla;

Psilopsida

(the

flowering plants).

Trade Winds
Winds

blow regularly from subtropical areas of high

pressure towards areas of low pressure along the equator,
in the northern hemisphere from the northeast, in the southern hemisphere from the southeast; important in producing
that

ocean currents.

Transad

species, or closely related species, that exist on both

sides of a barrier and consequently must have extended across
it

at

one time.

Transect

A long, narrow sample area, or a line,

351

used for analyzing

vegetation; essentially a cross section of the vegetation,

cf.

Line-intercept method. Quadrat.

Transformation

The change
as

when

DNA

to

Type

II it

of one type of bacterium to another type,

from Type I of Pneumococcus is transferred
replaces some of the Chromatin in the latter

whose characteristics such as resistance to Penicillin may

thus be modified. Genetic information is thus transferred.

Transgressive
Species that regularly occur in an upper layer in a community found also in a lower stratum.

Transhumance
The periodic and

alternating movement of livestock

differ in climate.

between two regions that

Transient Species

species that migrates through a locality without breedor

over-wintering.
ing

Transition Life-Zone

The

northern part of the Austral life-zone

(q. v.).

Translocation

The movement

from one
part of a plant to another part. cf. Xylem, Phloem. (2) The
separation of a part of a Chromosome and its attachment to
(1)

of materials in solution

another one.

Transpiration

The

loss of

water in vapor form from a plant, mostly

and lenticels. cf. Stoma, Lenticel.

through the stomata

Transpiration Coefficient

The

ratio of the oven-dry material

produced by a plant

during a more or less extended period of time (usually the

entire growth period) to the total amount of water transpired
during the same period.
352

Transpiration Efficiency
The amount in grams of dry substance produced by a
plant for every kilogram of water transpired.

Transplant

A seedling, or young plant, that has been moved from one

location to another; in forestry practice a seedling that has

been transplanted one or more times in the nursery.

Transportation (in Soil Erosion)

The movement of detached particles or masses
across the land or

of soil

through the air by wind, water, or gravity.

Trap Line

A series of traps arranged in a more or less linear arrange-

to secure a sample of the mammals in an area, or for

securing animals for their fur, or some other purpose.

ment

Traumatic
Refers to a shock or a wound, or the resulting condition
in an organism.

Travertine

calcareous,

formed in water,

concretionary
cf.

limestone

that

has

been

Sinter, Tufa.

Tree

A woody plant that has a single main stem and commonly

more than

eight or ten feet

tall. cf.

Shrub.

Tree Limit (Line)

The

altitude in mountains, or the southern or northern

which only isolated trees grow and beyond which

stunted
forms, Krummholz (q. v.), or Tundra (q. v.)
only
latitude, at

occur,

cf.

Timber line.

Tremotode
cf.

Fluke.

353

Trtassic

The oldest geologic period in the Mesozoic era; it began

about 205 million years ago and lasted for about 40 million
years.

Tribe

group of plants of related genera, a division of the

the tribe Festuceae includes the genera Poa,

Family,

e.g.,

Festuca,

Bromus, and

others.

Triploid
An organism or one of its parts that has three times the
Haploid set of Chromosomes in the nucleus, cf. Polyploid.

Trisomic
Refers to an organism that has one more Chromosome
(q. v.) number; occurs in barley, and peas.

than the Diploid

Tristat

Method

method

of photographing the

periods of time by permanently

each leg of the tripod is set

same area

at successive

marking the spot where

Trophic (-trophy)
Refers to nutrition.

Trophic Level

One

of the parts in a nutritive series in an Ecosystem

(q. v.) in which a group of organisms in a certain stage in
the Food chain secures food in the same general manner.

The

or lowest trophic level consists of Producers

(green plants), the second level of Herbivores, the third
level of primary Carnivores, the fourth level of secondary
first

Carnivores. Bacteria and fungi are organisms in the

poser

Decom-

trophic level.

Trophobiosis

type of association of species involving aphids

coccids with ants. cf. Myrmecophilous.

354

and

Tropholloxts

The exchange

of food, or the interchange of a stimulus

response concerning food, between animals, especially in the
social insects.

Tropical Cyclone
See Hurricane.

Tropical Life

Zone

The
life

portion of Central America south of the Austral

zone (q. v.), bounded on the north by an accumulation

of temperatures during the growing season above 43 F. of

26,000F. cf. Life zone.

Tropics

The Tropic

of Cancer,

2327' north

latitude,

and the

/
Tropic of Capricorn, 2327 south latitude; or the region
between these parallels.

Tropism
The curvature

response of an organ to a stimulus, e.g.,

a stem growing towards a source of light and roots away from
the light.

Tropoparasite

An

Obligate parasite (q. v.) that regularly lives as a nonparasite during part of its life cycle.

Tropopause
The uppermost

portion of the Troposphere

(q. v.).

Tropophyte

A plant

that can live under moist conditions pan of the

and
under
year
dry conditions during another part, e.g.,
woody plants that lose their leaves during the dry parts of

the year or during winter.

Troposphere
The part of

the atmosphere extending

355

upward about

six miles to the Stratosphere (q. v.), in

which clouds of

moisture form and the temperature decreases with increasing altitude.

Tropotaxis

The

an organism in response to two

lights that are moving toward or away from the midpoint
between them. cf. Telotaxis.
direct orientation of

True Prairie

The prairie grassland characterized by tall grasses (five

to six or more feet tall) and mid-grasses (two to four feet
tall) in the central part of the United States, cf. Pampas.
Truffle

Underground fungi
cetes,

in the genus Tuber, class

Ascomy-

or their fruiting bodies, edible.

Truncated Soil Profile

Soil profile (q. v.)

A and B

horizons (q.

which has
v.)

lost part

or

all

of the

by accelerated erosion or by

cultivation.

Trypanosome

flagellated

Protozoan in the genus

Trypanosoma,

parasitic in the blood of various Vertebrates, and causing

serious diseases in man and other animals such as sleeping
sickness.

Tsetse Fly

dipterous insect in the genus Glossina, sucks blood and

transmits diseases caused by Trypanosomes such as sleeping
sickness.

Tsunami

high wave on shore areas, particularly bordering the

Pacific Ocean, caused by an earthquake in the ocean floor.

356

Tuber

An

enlarged, underground stem, tending to be oval or

spherical in shape, usually rich in starch, and capable of
vegetative reproduction of the plant,

e.g.,

a potato tuber.

Tufa

porous rock formed by the deposition of material,

especially calcium carbonate from water, as in springs, cf.
Travertine, Sinter.

Tularemia

disease in rabbits, rodents,

and man, caused by the

microorganism Pasteurella tularensis, which

by

is

transmitted

insects.

Tullgren Funnel

A modification of the Berlese funnel (q. v.)

Collembolons
from the soil.

(q. v.),
cf.

Tundra
The treeless
from bare area

for separating

Mites, larvae, and other small organisms

Baerman

funnel.

land in arctic and alpine regions, varying

to various types of vegetation consisting of
dwarf shrubs, mosses, and lichens.

grasses, sedges, forbs,

Turbidity

The

condition of a body of water that contains suspended

material such as clay or silt particles, dead organisms or their
parts, or small living plants and animals.

Turf

The

layer of low, dense grassland, comprising the above-

ground portions and the upper roots and rhizomes with

tached

soil particles, cf.

at-

Sward, Sod.

Turgid

The condition of a cell or a tissue when

with water causing Turgor pressure (q. v.).
357

it

is

swollen

Turgor Pressure
The actual pressure
cell wall resulting

of the sap within a cell against the

from the intake of water by Osmosis

(q. v.).

Turion

winter

bud on some water

tached, overwinters,

into a

new

plants that becomes deand under favorable conditions develops

plant.

Turnover
(1) The mixing

of layers of water in lakes in the spring

Thermal stratification. (2) The period of

time required for an organism to grow, mature, die, and
undergo decomposition.

and autumn,

cf.

Tussock

plant-form that is tufted, bearing many stems arising as

a large, dense cluster from the crown, e.g., a large bunch
grass such as Arizona fescue.

Twin Communities
Communities that are similar in a dominant or combining

layers,

or in Synusiae

(q. v.),

but vary in others.

Tychocoen
See Ubiquist.

Type
(1)

kind of vegetation,

e.g.,

Community-type, forest

type, birch type. (2) The one or more specimens of a species,

subspecies, or variety on the basis of which the Taxon was

described. (3)
e.g.,

Miami

One

silt

of the groups of soils in a soils series,

loam type in the Miami

series.

Typhoon

Tropical cyclone or Hurricane

particularly in the China Seas.

858

(q. v.) in

the Far East,

Ubiquist (Ubiquitist)

An

organism that flourishes in several kinds of commured maple tree.

nities or ecosystems, e.g., the raven,

Ubiquitous
Refers to a Ubiquist.

Ultrasonic
See Supersonic.

Ultraviolet Radiation
The electromagnetic waves not perceptible to the human
eye, between violet light waves and X-rays, from about
390 mu to 10 mu in length.

Unconformity

An

irregular line of contact between

two geological

strata

caused by exposure to erosion of the lower one before submersion and consequent deposition of the second stratum.

Underdispersion
See Hypodispersion.

Undergrazing

An

intensity of grazing

by

livestock in

359

which the forage

available for consumption

is

not used

sufficiently,

under good management

practices

thus causing loss of forage.

Undergrowth
Collectively the shrubs,
trees,

and

all

sprouts,

herbaceous plants in a

seedling and sapling

forest.

tlnderpopulation

A size of population so low in number of individuals that

mortality is greater than in denser populations largely

because of increased exposure to unfavorable environmental
conditions.

Undershrub

low shrub.

Understocked
Refers to a range area on which a smaller number of
is
present than it is capable of supporting adefor
a
given season, cf. Fully stocked. Overstocked.
quately
livestock

Understory
Collectively the trees in a forest
cover, cf. Overstory.

below the upper canopy

Uneven-aged
Refers to a forest in which considerable differences in
the ages of trees occur.

Ungulate

A Mammal with hooves,

e.g.,

horse, cow, swine, elephant.

Unicellular
Refers to an organism that consists of only one
e.g., blue-green algae, Protozoans.

cell,

Union

A homogeneous grouping of plant species within a given

stratum or of the same or closely similar life-forms, cf.
Synusia.

360

Uniparous
Refers to an animal that produces only one egg or one
offspring at one time.

Unisexual
Refers to an organism that

is

either

male or female,

cf.

Hermaphrodite.

Univoltine
Refers to an organism that has only one generation in a
year. cf. Multivoltine , Diapause.

Unpalatable
Refers to plants and other kinds of food that are not
readily eaten by animals.

Unspecialized
Not Specialized

(q. v.).

Upper Austral Life Zone

One of the divisions in Merriam's Austral

Upper Sonoran
See Sonoran

Life

life

life

zone

(q. v.).

Zone

zone.

Use, Actual

The total number and period of time livestock graze

on a range, usually expressed as animal-unit months, cow
months, or sheep months.

Use,

Common

The

practice of grazing a given range by more than

kind of livestock within the same grazing year.

one

Use, Dual

The

grazing of a range area by more than one kind of

same time, such as cattle and sheep.

livestock at the

Use, Proper

The

utilization of a

Range

so that the Condition

maintained in a good to excellent rating.

361

is

Vacuolated
Refers to a cell that contains one or

more

Vacuoles.

Vacuole

space within a cell, enclosed by a membrane and

containing a watery solution, the cell sap, surrounded by

protoplasm.

Vacuole, Contractile
A structure in some

one-celled organisms that excretes

water by means of energy supplied by the Cytoplasm.

Vagility

The

capability of

an organism for Dispersal

(q. v.).

Valence, Ecological
See Ecological amplitude.

Valley Train
Materials carried beyond a glacial ice-front by streams
of melt water and deposited over a narrow area within a
valley.

Van't Hoff Rule

SeeQw.
362

Vopor Pressure
The

Deficit

between the actual vapor pressure in the

atmosphere in a certain space and the vapor pressure at
difference

saturation.

Variant

An

organism, community, types of soil, etc., that differs

or
sufficiently in its attributes from the typical specimen
norm to be classified as a variation of the group as a whole.

Variate

The
that

is

attribute or characteristic such as height and weight

used in statistical measurements of Variation.

Variation
Divergences in the characteristics of organisms, or other
objects, of the same kind caused either by the environment
or by differences in the genetic constitution of the organism,
cf.

Phenotype, Genotype.

Variegation

The

irregular occurrence of patches, bands, or other

areas on the surface of organs of plants and animals, such as
leaves, caused chiefly by the lack of pigment in the cells of

these areas or beneath them.

Variety

A taxonomic group or

a Subspecies,

e.g.,

(Burgsd.) Rydb.

cf.

Taxon (q. v.) within a Species, or

Juniperus communis L. var. sibirica

Cultivar.

Varve

layer in a mass of lacustrine sediments, which may

consist of coarser and finer sediments, deposited annually

in a lake or sea.

Vascular
Refers to vessels or ducts that conduct fluids in organisms.

363

Vascular Bundle

strand consisting of

Xylem

(q. v.)

and Phloem

(q. v.)

in plants.

Vascular Cylinder

vascular bundle with associated tissues in stems

roots of plants,

and

cf. Stele.

Vascular Plant

A plant

phylum Tracheophyta which includes the

pteridophytes (ferns and their allies) and the spermatophytes
in the

(seed plants).

Vector

An

organism, usually an insect, that transmits a patho-

genic virus, bacterium, protozoon, or fungus

ism to another, e.g., Tsetse fly (q. v.).

from one organ-

Vegetable Ball

more or less spherical mass of plant material consistof

ing
algae, other water plants, needles of trees, etc., formed
wave
action in shallow water on sandy shores.
by

Vegetal
See Vegetative.

Vegetation
Plants in general, or the
area. cf. Flora, Floristic,

sum

total of plant life in

an

Community.

Vegetational
Refers to Vegetation, in contrast to Vegetative

(q. v.).

Vegetation (Vegetational) Cover

The sum total of plants and plant
leaves, stems,

and

fruits that

materials such as
forms coverage on the surface

of the soil; sometimes used in a

designate the

sum

of living plants

364

more
on an

restricted sense to
area.

Vegetation (Vegetational) Type

(q.

kind of Vegetation (q. v.) or the kind of Community

v.) of any size, rank, or stage of Succession.

Vegetative (Vegetal)
Refers to the nutritive and growth functions or structures
of plants in contrast to the reproductive functions or struc-

not to be confused with Vegetation or Vegetational

v.). cf. Somatic.

tures;
(q.

Vegetative Propagation
The propagation, or increasing

the number, of plants by

the use of Vegetative parts such as rhizomes (q. v.), runners

gemmae, or other parts, cf. Asexual reproduction.

(q. v.),

Vein

See Vascular bundle. (2)

Vessel in animals that
carries blood from the capillaries to the heart. (3) A thick(1)

ened structure that gives support

to

wings of

insects.

Velamen

tissue in the outer part of aerial roots of certain plants,

especially orchids, that absorbs water rapidly.

Veld (Veldt)

tract of

open country in South Africa occupied by

and by Scrub or Savanna

grasslands at the higher elevations

at the lower elevations.

Venation
The arrangement

of Veins in a leaf blade or in a

wing

of insects.

Verano
The long,

dry period of the year in tropical America.

Vermiform
Refers to a shape of an object that

365

is

similar to a

worm.

Vernal
Refers to spring,

cf.

Aspection.

Vernalization

The

process of hastening the flowering phase of plants

by subjecting young seedlings or other parts

ture, less

commonly

Versant
The general

to

low tempera-

to a high temperature.

slope of a

mountain range or a landscape.

Vertebrate

An

animal in the subphylum Vertebrata, phylum Chor-

data, e.g.,

mammals,

fishes, reptiles, birds.

Vesperal
Refers to evening time.

cf.

Crepuscular.

Vessel

series of cells

Xylem

(q. v.)

forming a tube-like structure in the

of plants, conducts water

and substances in

solution.

Vestigial
Refers to a structure, function, or behavioural act of an
organism that has so decreased in importance during the
course of evolution that only a trace remains,
form appendix in man. cf. Primitive.

e.g.,

the vermi-

Viability

The

capability of a seed, spore, egg, or other organ of a

plant or animal to continue or resume growth when it is

exposed to favorable environmental conditions, cf. Dormancy.

Viable
Refers to the state of being alive,

cf.

Viability.

Vicariad (Vicarious Species)

One
Taxon

of a pair of closely related species, variety, or other

that replace each other geographically.

366

VIcoriation

The phenomenon

of ecologically equivalent species, or

taxonomically corresponding species, replacing (or "substituting") each other in similar environments in different

geographic areas,
deer in Eurasia.

e.g.,

caribou in North America and rein-

Vicinism

The

condition of variation in a population or in an

individual resulting from growing in close proximity to

other organisms.

Virgin (Forest, Community, Region,

etc.)

Refers to objects or aggregations, especially vegetation,

essentially uninfluenced by human activity.

Virology

The branch

of biology dealing with viruses.

Virus

submicroscopic parasite in organisms consisting of

and protein, incapable of increasing in number

outside of the host cell, causing various diseases in plants
and animals.
nucleic acid

Vitalism

The doctrine that life processes are caused by some force

that cannot be measured, in addition to the operation of the
laws of chemistry and physics.
Vitality

The

condition of vigor of organisms; the capacity to live

and complete the life cycle. Braun-Blanquet classified plants
according to states of vitality into four categories.

Vitamins
Organic substances required in minute quantities by
plants and animals in their metabolic processes, cf Thiamine.
.

867

Viticulture

The

cultivation

and production of

grapes.

Viviparous
(1)

Refers to an animal in which the embryo develops

its body and which produces

living offspring, e.g.,
most mammals, cf. Oviparous. (2) Refers to a plant in which
the embryo within the Ovary continues development without
interruption, e.g., the mangrove; or the production of
Bulbils or small plants instead of flowers and seeds, e.g.,
bulbous bluegrass.

within

Volume Weight

soil,

figure denoting the

number

including the pore space,

water,

cf.

Bulk

density.

368

is

of times heavier a dry

than an equal volume of

w
Wadi (Wady)

A watercourse in deserts, dry except after rains, term

used in southwest Asia and the Sahara, cf. Arroyo, Wash.

Wallace's Line

The

by A. R. Wallace (1860) as a
boundary between the Oriental and the Australian Faunal
line

regions (q.

established

v.).

Warm-bloodedness
See Honuoio therm.

Warm

Front

The border between

a mass of

or above a mass of colder

air. cf.

warm

air

advancing into

Cold front.

Warning Coloration
See Aposematic.

Wash
In southwestern United States, a dry bed of an intermittent stream, usually sandy and gravelly.

Wasting Disease

disease of eelgrass (Zostera marina) often producing

serious epidemics, caused

by a Slime mold (Labyrinthula sp.).

369

Water Gap

hills,

narrow valley or gorge in a ridge of mountains or

eroded by a stream, e.g., the Delaware Water Gap.

Water-holding Capacity
The amount of water, stated as

the percentage of oven-dry

soil, that is retained by the soil after the gravitational water
has drained off. cf. Field capacity.

Waterlogged
The condition
filled

of a soil in which

all

the pore spaces are

with water.

Water Requirement
The

ratio of the

number

of units of water absorbed by

a plant during the growing season to the number of units

of dry matter produced by the plant during the same time,
cf.

Transpiration coefficient.

Watershed
(1) The total

area of land above a given point on a

waterway that contributes run-off water to the flow at that

point. (2)
major subdivision of a drainage basin.

Waterspout

tornado-like vortex

and cloud occurring over a body

of water.

Water Spreading
The application by means of stream diversion or otherwise of water over the land in order to increase the soil
moisture supply for the growth of plants or to store
ground for subsequent withdrawal by pumping.

it

under-

Water Table
The upper

surface of the free

ground water in a zone

of saturation, except where it is separated by an underlying

body of ground water by unsaturated material.

370

Water Table, Perched

The upper

body of free ground water in a

zone of saturation, separated by unsaturated material from
another body of ground water in a saturated zone beneath,
cf. Perched water.
surface of a

Weather
The

atmosphere at any given time with retemperature, humidity, cloudiness,

gard
wind movement, and barometric pressure, cf. Climate.
state of the

to precipitation,

Weathering
The process
of rocks

of the physical

and chemical

disintegration

and minerals.

Weed
A general

term for any troublesome or otherwise undesirable plant, usually introduced, grows without intentional

cultivation.

Wegener's Hypothesis
See Continental

drift.

Weir

A dam across a water channel for diverting or for measuring the flow of water.

Westerlies
Winds that blow

prevailingly

from the southwest in the

northern hemisphere, from the northwest in the southern

hemisphere, located between the high pressure areas of the
Subtropics and the arctic or antarctic circles.

White Alkali
See Saline

soil.

Wilderness Area
See Natural area.
371

Wildlife
Collectively

except

fishes,

the

non-domesticated vertebrate animals,

such as deer, moose, birds,

etc.

Wildling

seedling or a young plant that grew under natural

conditions, not cultivated, outside of a nursery, and that

has been

dug

WilHwaw
A sudden

for use as planting stock.

blast of

wind descending from mountains

to

the sea, especially in the Straits of Magellan.

Willy-willy

A violent

storm of rain and wind on the northwest coast

of Australia; also applied in

local

Dust whirl

some

parts of Australia to a

(q. v.).

Wilting

The temporary or transient loss of turgidity in a plant

caused by a rate of transpiration in excess of the rate of
absorption of water. Permanent wilting: wilting to such a
degree that plants do not recover unless water is added to
the soil soon after wilting occurs. Permanent wilting percentage (wil ting-point, wil ting-coefficient): the water remain-

ing in the soil in percentage of dry weight of the soil

the plants are in a condition of permanent wilting.

when

Windbreak

A planting of

trees

and shrubs, usually

in three or

more

rows to serve as a barrier to reduce or check the velocity of

the wind. cf. Shelterbelt.

Winter Annual

plant that germinates in the autumn, lives through

the winter as a small plant usually, renews growth in the
spring, flowers, produces fruit,

and then

372

dies.

Wireworm
The

larva of certain slender beetles as in the genus

Agriotes.

Witches'

Broom

The abnormal

brushlike production of numerous weak

shoots toward the tip of a branch of a tree or a shrub, caused

by a fungus or a mite.

Woodland
Any

land used for the growth of trees and shrubs such

permanent woodland cover, plantings along roadsides and

stream banks, Shelterbelts, farm Woodlots, etc.
as

Woodlot

small area of land occupied by trees.

Working Depth
The depth

(Roots)

which a large number of roots

Depth, effective soil.

in the soil to

of a plant penetrate,

cf.

373

Xenia

An effect produced in the offspring in the endosperm of

a seed brought about by the fusion of one of the sperms with
the Diploid fusion nucleus in the Ovule.

Xenogamy
See Cross-pollination.

Xerorch
Refers to a successional sequence (Sere) which begins in
a dry habitat, cf. Xerosere, Hydrarch.

Xeric
Refers to a dry habitat, cf Xerocolous, Xerophyte, Hygric,
.

Mesic.

Xerochase

A seed pod
e.g.,

that opens in dry air. and closes in moist air,

carrot seed pods.

Xerocolous
Refers to animals living in dry places,

Hygrocole.

374

cf.

Xerophilous,

Xeromorphy
The
phytes

(q.

form

characteristic of organs of Xerodesert

e.g., tough, leathery leaves on some

structure or
v.),

shrubs.

Xerophilous, Xerophytic
Refers to a plant that
e.g., cactus, cf.

is

capable of growing in dry places,

Xerophyte, Hydrophilous, Mesophyte.

Xerophyte

plant that can grow in dry places,

cactus,

cf.

e.g.,

creosote bush,

Xerophilous.

Xeroplastic
Refers to characteristics which are developed under the
influence of drought.

Xerosere

A
cf.

series of successional stages

beginning in a dry area,

Hydrosere, Sere, Xerarch.

Xerothermic
Refers to a dry and

warm

climatic period,

e.g.,

one of

the postglacial periods.

X-rays
Electromagnetic rays, 0.1 to 50 mu, shorter than Ultraand longer than Gamma rays.

violet

Xylem
Woody

tissue in the Stele (q. v.) of plants,

and substances in

solution.

Xylophagous
Refers to organisms that consume wood.

375

conducts water

Yeasts
One-celled plants in the class Ascomycetes, phylum Eumycophyta, the true fungi, reproduce vegetatively by budding,

and convert sugar

to alcohol

and carbon dioxide in An-

aerobic respiration.

Yield

The

part of the production or Productivity (q. v.) of a

of
group
organisms that is removed or expected to be removed by man, e.g., the number of deer killed during a

hunting season, the timber produced by a stand of

Yield Table
A table showing the volumes of timber
trees

will

trees.

that a stand of

produce at different ages (usually in ten-year

periods) per unit of area.

Young Growth
See second growth.

376

Zonal
Refers to Zone.

Zonal

Soil

kind of

soil

that has a

permanent type of

profile,

characteristic of the prevailing conditions of the climate

vegetation,

e.g.,

Chernozem

(q. v.). cf.

Intrazonal

and

soil.

Zone
(1) Vegetation occurring in more or less well marked belts
or areas much longer than wide, usually fairly uniform in
physiognomy, as along lake shores, mountain sides, and sea

the two

One

of the five great climatic belts of the earth;

frigid zones, two temperate zones, and the torrid

shores. (2)

zone.

Zoochore

An
cf.

organism that

is

normally disseminated by an animal,

Diaspore.

Zoogeography
The

science that deals with the geographic distribution

of animals,

cf.

Biogeography, Plant geography.

377

Zoology
The study

of animals.

Zoophagous
Refers to organisms that feed

on substances

of animal

origin.

Zooplankton
Animals occurring in Plankton

(q. v.).

Zoospore

A motile spore,

algae

and

possessing one or

more

flagella, in certain

fungi.

Zygomorphy
See Bilateral symmetry.

Zygote
The product
the fertilized egg.

resulting

from the union of two gametes;

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Alee,

W.

C.,

A. E. Emerson, O. Park, T. Park, and K. P.

W. B. Saunders

Schmidt. Principles of Animal Ecology,

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Andrewartha, H. G., and L. C. Birch. The Distribution and

Abundance
Chicago,
Becking, R.

111.,

of Animals,
1954.

W. The

University of Chicago Press,

Zilrich-Montpellier School of Phytoso-

ciology, Botanical Review, vol. 23 (1957), pages

Plant Sociology, McGraw-Hill

Braun-Blanquet, J.
Inc., New York, N. Y., 1932.

411488.

Book

Co.,

Brown, Dorothy. Methods of Surveying and Measuring

Vegetation, Bulletin 42, Commonwealth Bureaux Pastures and Field Crops, Hurley, Berks, England, 1954.
Cain, S. A. Foundations of Plant Geography, Harper and
Bros., New. York, 1944.
Cain, S. A., and Q. M. de Oliveira Castro. Manual of Vegetation Analysis, Harper and Bros., New York, N. Y., 1959.
Clarke, G. L. Elements of Ecology, John Wiley & Sons, Inc.,
New York, N. Y., 1954.
Clements, F. E. 'Plant Succession, Carnegie Institute of Washington Publication 242 (1916), Washington. D. C.
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&

Sons,

E.,

New

and V.

E. Shelford. Bioecology,
York, N. Y., 1939.

John Wiley

Dansereau, P. Biogeography. An Ecological Perspective,

Ronald Press, New York, N. Y., 1957.

The

Darlington, P. J., Jr. Zoogeography: the Geographical Distribution of Animals, John Wiley & Sons, New York,

N.

Y., 1957.

and Environment, a Textbook of

Plant Autecology, John Wiley & Sons, Inc., New York,
N. Y., 1959. 2nd Edition.
Dayton, W. A. Glossary of Botanical Terms Commonly Used
Daubenmire, R.

F. Plants

Range Management, U. S. Dept. of Agriculture Miscl.

Publication No. 110 Revised (1950).
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Dice,

Lee R. Natural Communities, University of Michigan

Ann

Arbor, Mich., 1952.

Dodson, E. D. Evolution: Process and Product, Reinhold
Publishing Corporation, New York, N. Y., 1960.
Ecological Society of America. Reports 1, 2, 3, of the
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Committee

on

Nomenclature,

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1934,

1935).

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Eggleton, F. E. Report of the Committee on Nomenclature
of the Ecological Society of America, Revised. (1952).
(Photoprinted).
Esau, Katherine. Anatomy of Seed Plants,
Inc., New York, N. Y., 1960.
Giese, A. C. Cell Physiology,
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W.

John Wiley &

Sons,

B. Saunders Co., Philadel-

Good, R. The Geography of Flowering Plants, 2nd Edition,

Longmans, Green & Co., London, England, 1953.
Hanson, Herbert C. Ecology of the Grassland H, Botanical
Review, vol. 16 (1950), pp. 283-360.
Hanson, Herbert C., and E. D. Churchill. The Plant Community, Reinhold Publishing Corporation, New York,
N. Y., 1961.
Hawley, A. H. Human Ecology, The Ronald Press Co., New
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380

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Macfadyen, A. Animal Ecology, Aims and Methods, Sir Isaac

Pitman & Sons, Ltd., London, England, 1957.

The Species Problem (A Symposium),

American Association for the Advancement of Science
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Philadelphia, Pa., 1949.

Meyer, B. S., D. B. Anderson,
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N.

J.,

Odum,

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1960.

E. P.

Fundamentals of Ecology, 2nd Edition,

W.

B.

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The Study of Plant Communities, 2nd Edition,
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Principles and Pracand

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Department of Agriculture. Soils, the Yearbook of

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Government

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382

McGraw-

Pictorial History
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DAGOBERT

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DICTIONARY OF
PHILOSOPHY
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DAGOBERT

Edited by

"This book
that

RUNES

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editor

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REV. JAMES F. CARROLL,

C.S.Sp.,S.T.D.

Dean, Graduate School,

Duquesne University