Unit- I, PLANT

PHYSIOLOGY
Structure and Germination
of Seeds
conditions for seed germination.
Sylabus : Structure of dicot and monocot seeds. Germination of seeds, types, and
DCope of Sylabus
" Differences :Structure
between and gemination
monocot and dicot seeds. ofDifferences
Beanseedbetween
and Maize grain. and epigeal germination.
hypogeal
" Conditions for seed germination To be expained and supported by expem
3
INTRODUCTION (2) The embryo (Fig. 5.1) - An embrvo
defined as a young miniature plant along with
seed coat.
n the life of flowering plants, seeds are very cotyledóns, enclosed within the The
Limportant structures as they help in the embryo is differentiated into
formation of new plants, A seed is a mature ovule (A) cotyledons and (B) embryo
axis
after fertilization. The ovule develops rapidly after PLUMULE

fertilization using the food reserves. In addition -EPICOTYL

to the development of new plants, seeds also help SEED COAT
in the dispersal ofa species as well as overcoming
ENDOSPERM
unfavourable conditions. -COTYLEDON

5.1 STRUCTURE OF SEED (Fig. 5.1) COTYLEDON STALK

(MESOCOTYL)
HYPOCOTYL
All seeds have some common features. Though,
they vary in size, shape, colour and some other -RADICLE
features. A typical seed is differentiated into three
parts i.e. Fig. 5.1 ::Structure of generalized seed

(1) Seed coat (2) Embryo (3) Stored food. (A)Cotyledons - Also called seed leaves, they
(1) The seed coat - Each seed is covered by are either two (in dicotyledonous plants) or one (in
a protective covering called seed coat. It develops monocotyledonous plants) in number:. They are food
from the integument of ovule. The seed coat is laden, fleshy structures attached to the embryo axis.
differentiated into an (i) outer tough, protective testa They provide nourishment to the embryo in the
and (ü) inner thin tegmen. The testa protects the early stages of development. In endospermic seeds
seed from dessication,bacteria, fungi and insects. cotyledons are not massive e.g., castor.
(B) Embryo axis - It is the young or miniature
On the seed is present a scar called hilum. It plant differentiated into the following parts :
represents the point of attachment of the seed with
(a) Mesocotyl - It is a part of the embryo axis
its stalk. Adjacent to the hilum is present a minute where cotyledons are attached.
opening called micropyle. (6) Epicotyl - It is a portion of the embryo axis
Absorption of water as well as exchange of gases between the mesocotyl and plumule.
take place through the micropyle during germination (c) Hypocotyl - It is a portion of the embryo
of seed. The micropyle is not easily seen in a dry between mesocotyl and radicle.
seed, But, if a seed, soaked in water is pressed gently. (d) Plumule - It is the feathery or leafy end of
through this the embryo axis that grows into shoot systen
some water and air-bubbles o0ze out
pore and it can be easily
located. of the plant.

Candid KCSE Bioiogy 3

 (c) Radiele-It is the pointed lower end of the embryo axis that develops into the root system of aplant.
3. Food storage in the seeds The seeds contain stored food material to be used during early
development. The food is stored either in the cotyledons or in a special food storage tissue called the
endosperm. The seeds in which food is stored in the cotyledons and contain no endosperm are called non
endospermic or exalbuminous e.g. bean, gram, pea, alisma e.g., castor, cotton, maize, wheat, rice Whereas,
those seeds which contain stored food in the endosperm are called endospermie or albuminous seeds.
Types of seeds
Depending upon the number of cotyledons and presence or absence of endosperm, seeds are classified as
shown in Table 5.1.
Table 5.1 Types of seeds
SEEDS

Dicotyledonous Monocotyledonous
(Two cotyledons) (One cotyledon)

Exalbuminous Albuminous Exalbumlnous Albuminous

(without endospem) (having endosperm) (without endosperm) (having endosperm)
e.g. bean, gram, pea, etc. .g. castor,cotton, etc. .g. Allsma 9.g. malze, wheat, rlce, etc.

5.1.1 Structure of bean seed-a dicotyledonous of the stalk (funiculus) which remains fused with
exalbuminous seed (Fig 5.2) the testa.
Bean seeds are kidney-shaped being convex on To study the internal structure of bean seed, it is
one side and concave on the other. The following soaked in water for a few hours. The soaking makes
external features are seen in the bean seed: the seed coats soft and easy to remove. On removing
1. Seed coat - Bean seed is surrounded by two the seed coat we find the embryo.
seed coats that develop from the two integuments of 5. Embryo - The embryo consists of the
the ovule. These two coats are : following parts:
(a) Testa - It is the outer, smooth, thick and (a) Cotyledons - The bulk of embryo consists
coloured protective layer. It protects the of two fleshy structures called cotyledons. These
seed from fungi, bacteria and insects. store the food and provide nourishment to the
(6) Tegmen - It is thin, white, membrane.like developing embryo axis. The bean seeds do not
inner seed coat. It is very firmly fused with contain endosperm, and thus are non-endospermic.
the testa. It is often very difficult to separate (b) Embryo Axis - In between the two
it from the testa. cotyledons is present, a young miniature plant called
2. Hilum - On the concave side of the seed is embryo axis. It is differentiated into :
present a scar called hilum. It is the point from (i) Mesocotyl - part of the embryo axis where
where the seed is attached to the pod with the help cotyledons are attached laterally.
of a short stalk called funiculus. On maturity, the (i) Epicotyl - portion of the embryo axis
funiculus detaches and leaves behind this scar. between mesocotyl and plumule.
3. Micropyle - Adjacent to the hilum is present (ii) Plumule - the feathery or leafy end of the
a very minute pore called micropyle. Absorption of embryo axis that later grows into shoot
water and exchange of gases take place through the system.
micropyle during germination of seeds.
4. Raphe - It is a ridge-ike structure present (iv) Hypocotyl - portion of the embryo axis
around the median groove. It represents the portion between mesocotyl and radicle.

Stracture and Gemination of Saads 63

 i.e. the upper large

TESTA
distinct regions
the lowersmaller embryo. These are separated
prominent epithelial layer.
endosperm
forms the bulk of
-MICROPYLE 8. Endosperm - It the grain
as reserve food
and stores starch material.
endospermis surrounded by a special The
one-prceolte-tihnigc,
HILUM

layer. It is rich in
layer called aleurone

(a) External Structure

PLUMULE COTYLEDON
-ENDOSPERM
EPICOTYL
POSITION
EMBRYO
OF
HYPOCOTYL
-RADICLE

POINT OF
ATTACHMENT
COB
TO
(b) Internal Structure
Flg. 5.2:Structure of bean seed (a) Extermal appearance

(v) Radicle - the pointed lower end of the PERICARP AND SEED
COAT (FUSED)
embryo axis that later grows into root
system of the plant. ENDOSPERM
5.1.2 Structure of maize seed (Zea ALEURONE LAYER
mays
- a Monocotyledonous albuminous seed -SCUTELLUM
(Fig 5.3) -COLEOPTILE
SLSAF
Maize is one seeded fruit called caryopsis. In PLUMULE
maize seed the fruit wall (pericarp) is fused with the
seed coat.
-RADICLE
The maize (corn) grain is a flat, almost
triangular
oblong structure. Externally it is differentiated in
COLEORHIZA

two unequal areas i.e., (b) L.S. of seed

Flg. 5.3 : Structure of maize seed
() A large,yellowish, upper area which marks the 4. Embryo - The embryo lies obliquely in the
position of endosperm lower small part of maize grain. It consists of :
(ii) Small whitish lower area that contains the (a) Cotyledon - The maize grain contains a
embryo. single, papery, shield-shaped cotyledon
The maize grain consists of the following parts : called scutellum, The scutellum does not
1. Fused seed coat and pericarp - The contain food. It is closely pressed against the
maize grain is covered externally by a thin but firm, endosperm.
(6) Plumule- It consists of the growing tip of
yellowish membranous layer. It is formed by the the shoot along with few embryonic leaves. It
fusion of seed coat and fruit wall or pericarp. is covered by a conical cap or plumule sheath
2, Hilum and micropyle - These are not called coleoptile.
distinguishable in maize grain. (c) Radicle - It lies at the base of the grain and
The internal structure of maize grain is studied is covered by root cap. It is surrounded by a
in alongitudinal section (Fig. 5.3 b). It shows two protective root sheath called the coleorhiza

64 Candid ICSE Biology 9

Table 5.2 Compaison between Bean seed and Maize arain
5.2.1 Conditions necessary for gernination
Bean Seed Maize GralD
4 Seed coat is thin and| 1. Seed coat is
Seeds will germinate only if suitable conditions
brownish in colour.
very thin and are available. The following favourable conditions
fused with pericarp. are necessary for the germination of seeds :
2. Hilum and miGropyle are 2. Hilum and micropyle are
visible. invisible. (1) Water (2) Availability of O, and
3. Two thick, leshy ootyledons 3. Single thin cotyledon present. (3) Moderate (favourable) temperature.
are present.
4. Endospem absent. 4. Endosperm present. Apart from these conditions, light also plays an
5 Reserve food is carbo-| 5. Reserve food material is
hydrates and proteins starch present in endosperm.
important role in seed germination.
present in the cotyledons. 1, Water - Dry seeds contain only 10% to 20%
6. Tips of plumule and radicle B. Tips of plumule and radicle water. They are incapable of germination as long
are naked. are covered by protective
sheaths called coleoptile and as sufficient quantity of water is not available.
coleorhiza respectively. Germination of seeds starts only after the rapid in
Table 5.3 Differences between monocot and dicot seeds take of water through the mieropyle and absorption
through their surfaces. Water intake helps the seed
Monocot seed Dicot seed togerminate in the following ways :
1. The seed contains single 1, The seed possesses two (i) It softens the seed coats and causes its rupture.
cotyledon. cotyledons. The plumule and radicle emerge out as they
2. The food is commonly 2. The food may be stored
stored inside the endosperm grow.
(exception-orchids) inside the endosperm or
3. An aleurone layer of special
cotyledons. (ü) It activates protoplasm and enhances metabolic
3. This layer is absent. activities.
protein rich cells is present
outside the endosperm. (iiü) It helps in the hydrolysis of stored food
4. The embryo tips may bear 4. Coleoptile and coleorhiza
special sheaths, coleoptile are absent. materials into simple and soluble state.
Over plumule and coleorhiza
Over radicle. (iv) It helps in the transportation of soluble food
5. Embryo occupies one side of 5. Embryo occupies the whole
the seed.
from storage tissue to the developing embryo.
interior or only the central
part of the seed. 2. Oxygen - During germination of seeds,
6. Plumule lies at one end near 6. Plumule lies in between the metabolic activities accelerate and require energy.
the cotyledon. two cotyledons. This energy is released from the stored food
materials by the process of oxidation. For this
5.2 SEED DORMANCY AND GERMINATION purpose, the seeds require oxygen. Because of
In most cases, the seeds are dry and incapable oxidation of food, oxygen is consumed and C0, is
of germination when shed from the parent plant. produced. This exchange of O, and CO, takes place
In this condition, all the metabolic activities are primarily through the micropyle.
taking place, but at the lowest rate just necessary 3. Temperature - Temperature plays an
for survival. A very small quantity of stored food is important role in the germination of seeds. Seeds
used. The seeds which do not germinate even when of different plants germinate at different optimum
provided with all the suitable conditions necessary temperature (temperature at which the seeds grow
for germination are called dormant seeds. most rapidly). Generally seeds of tropical plants
This phenomenon is termed as dormancy. It is need higher temperature, whereas, that of temperate
very important in overcoming the unfavourable climates need low temperature for germination.
conditions. It helps in the dispersal as well as 5.2.2 Process of seed germination
storage of seeds. The seed contains a dormant embryo. When it
Germination : is to germinate, rapid intake of water through the
The sum total of all the processes by which micropyle makes the seed large, swollen and the seed
the dormant embryo of the seed grows out of the coat becomes soft and bursts open.
seed coats and establishes itself as an independent Absorption of water induces a number of
seedling is called germination. When suitable physiological changes in the seed and enhances the
conditions are available and the embryo has respiratory activity. The embryo produces a large
Overcome dormancy, it becomes active and starts number of enzymes. These enzymes hydrolyse the
germinating. The process of germination is stored food matetial and make it available to the
irreversible. growing embryo. With the availability of food, cell
Stracture a G¡naton of Saads 65
 Inference
Proper germination of seed needs
of water as in
petri-dish A.
division starts in the embryo. Radicle and plumule adequate quantity
grow in size and emerge out of the seed coat. The absence of water,
seeds do not germinate In
radicle is the first to come out of the seed coat. It the Deficient and excessive water
forms the root system that grows into the soil. The in
petri-dish
does not allowB.the germination to continue because also
plumule after coming out of the seed coat forms available, once the O, dissolved in water
is not germinating seeds.
shoot system. As mentioned above. the germination isO,used up by the
of seeds requires sufficient quantity of water, air Precautions :
and optimum temperature. It can be proved by the dish must contain equal number Of
following experiments: () Each same source.
seeds from the
Experiment 1 the four petri-dishes must be subjected
Aim - To demonstrate that water is (ii)All
similar conditions of light and temperature
essential for germination of seeds. experiment.
Apparatus - Bean seeds (soaked and unsoaked), for the duration of the
four petri-dishes with lids, cotton wool or blotting should be kept covered witl
(iii) The petri-dishesevaporation of water.
paper, etc. lids to prevent
Procedure- Label the four petri-dishes as A, B, Experiment 2
temperaturs
C and D., Place the cotton wool or blotting paper and Aim - To study the effect of
seeds at the bottom of petri-dishes as follows : germination of seeds.
In petri-dish A - The cotton wool or blotting on Apparatus Three petri-dishes with lids
paper at the bottom should be moist. The seeds paper, soaked gram seed
placed on the moistened cotton wool should be cotton wool or blotting
thermometer.
soaked in water overnight. (Fig. 5.4 (a)]
In petri-dish B- Seeds are soaked in water but Procedure - Label the petri-dishes as AB
are placed on the cotton wool or blotting paper which and C. Place moist cotton wool or blotting paper
is not moistened. [Fig. 5.4 (b)] at the bottom of each petri-dish along with equal
In petri-dish C - Unsoaked seeds are placed on number of soaked gram seeds from the same sourc
the dry cotton wool or dry blotting paper. [Fig. 5.4(c)] (Fig. 5.5). Cover the petri-dishes with lids. Place
In petri-dish D - Soaked seeds are completely the petri-dish-A at room temperature, petri-dist
submerged in water. [Fig. 5.4 (d)] Bin a refrigerator while petri-dish Cin an oven a
temperature above 48°C. Maintain the temperatur
for few days.
3 Observations - Seeds germinate in the petr
A B
dish A whereas, fail to germinate in both the petr
(a) SOAKED SEEDS PLACED (6) SOAKED SEEDS PLACED dishes B and C.
ON MOIST COTTON WOOL ON DRY COTTON WOOL

A B
(a) SOAKED SEEDs WET COTTON (b)SOAKED SEEDs WET
D
AT ROOM TEMPERATURE COTTONAT 0°C
SEEDSWO0L
PLACED ON () SOAKED SEED SUBMERGED
(c) UNSAoTTON IN WATER
Fig. 5.4 :Experiment to show that water is
essential for germination of seeds
Observations - After keeping the above
petri-dishes at room temperature for 2-3 days, the (c) SOAKED SEEDs WET
following observations are made : COTTON AT 50°C

i) Seeds germinate properly in petri-dish A.

Fig. 5.5: Experiment to show the effect of
temperature on seed germination
(ii) Seeds may begin germination but shrivel up Inference Seeds germinate in petri-C
and die in petri-dish B. A because they were subjected to optim
the seeds.
() In petri-dish Cno change is seen in temperature. The seeds fail to germinate in
D the seeds may start
(ip) In petri-dish eventually petri-dishes B and C because of low and
germination but rot.
temperatures respectively. Low temperat
Candid ICSE Biolog
66
completely prevents the germination by restricting is partly submerged in water, whereas, lower seed (©)
the growth of embryo. High temperature destrovs is completely submerged in water. Place the beaker in
the growing tissue and thus prevents
germination. a warm, airy room for few days.
Experiment 3
GLASS SLIDE
Aim - To prove that oxygen is
for germination of seeds, essential
BEAKER
Apparatus - Two conical flasks, cotton wool or SEED A
blotting paper, soaked seeds of gram, two smalltest
tubes, thread, pyrogallic acid, NaOH, corks etc.
Procedure - Take two conical flaskS and label SEED B
them as A and B. Spread a moist cotton wool in WATER
each flask and place some soaked gram seeds on
-SEED C
it. Hang a small test tube containing
acid dissolved in NaOH in flask pyrogallic
A with the help
of a thread. In flask B is hanged similar test
but containing water. Close the mouths of bothtube
Fig. 5.7 :Three-bean experiment to prove that water, air and
the optimum temperature are necessary for seed germination
PYROGALLIC ACID
DISSOLVED IN NaOH
Observations
(1) The top seed (A) does not germinate.
WATER
(2) The middleseed (B) germinates properly.
MOIST
COTTON
(3) The lower seed (C) starts germinating but
SOAKED MOIST
SEEDS
COTTON germination soon stops.
Inference - The above experiment proves that
water and oxygen are necessary for the germination
of seeds. The middle seed (B) germinates as it
A both the water as well as oxygen. The top seedgets(A)
Fig. 5.6 :Experiment to prove that oxygen is does not germinate as it does not get water and gets
germination of seeds
essential for 0, only, whereas, the lower seed (C) gets water. The
flasks with air tight corks so that no air Oxygen dissolved in water is available to the seed
them from outside. Place both the flasks enters in in the beginning, hence, it starts
temperature for few days.
at room when O, dissolved in water is usedgerminating. But,
up by the seed, it
stops further germination.
Observations - Seeds do not germinate in flask In this experiment, the effect of
Awhereas, they germinate properly in flask B. temperature is
not proved directly. If a beaker similar to the one
Inference - The seeds do not as in above experiment is placed in the
flask A because the oxygen in it is germinate in or above 50°C, none of the three seeds refrigerator
the alkaline pyrogallic acid and is not absorbed by will undergo
the seeds. On the other hand seeds in available to germination. It will prove the importance of
Oxygen and hence, germinate.
flask B get optimumn temperature.
It explains why the seeds do not
germinate when placed
too deep in the soil or in the hard
Experiment 4 also and compact soil. It
explains why the farmers plough their fields before
Aim - To demonstrate that sowing seeds.
and optimum temperature are water, oxygen
the germination of seeds. necessary for 5.3 TYPESOF
(Three-Bean Experiment) The process GERMINATION
of germination is
Apparatus - A beaker half into two types depending categorizedof
upon the behaviour
glass slhde or wooden plate, thread,filled with water,
three bean seeds. cotyledons during germination i.e.
(1) Epigeal germination and (2)
Prooedure- Three bean seeds are tied to the germination. Hypogeal
glass slide or wooden plate as shown in Fig. 5.7
kept in a beaker half filled with and 5.3.1 Epigeal
In this type germination (Fig. 5.8)
water in such a way
that the top seed (A) is out of water, middle seed (B) of germination, the
lifted above the ground due to rapid cotyledons are
Structure and Gemination of Seeds elongation
67
 GROWING POINT

FIRST
LEAF
BUD
PRIMARY ROOT
EPICOTYL
COTYLEDON

WTHERED
COTYLEDON
CURVED
HYPOCOTYL STRAIGHTEND
HYPOCOTYL

FALLEN
SEED
cOAT
BROKÈN PRIMARY SECONDARY
SED `EED 4ROOT ROOTS
SEED COAT

(i (M) (v)

Fig. 5.8: Epigeal germination in bean Seed

of hypocotyl. The cotyledons turn green and form
the cotyledonary leaves. It is found in bean, castor, Note : In endospermic seeds like castor, the cotvlertone
enveloped by the endospem and testa rise into the air
papaya, cotton, sunflower, tamarind, etc. The cotyledons absorb all the food reserves from the
The various stages during epigeal germination of endosperm, which is then shed along with the testa. The
bean seed are summarized as follow : castor seeds contain caruncle (whitish structure at th
tip of the seeds) has agreater water absorbing capacity
() Under favourable conditions, the seed absorbs
large quantities of water and swells up. 5.3.2 Hypogeal germination (Figs. 5.9 &5.10)
(iü) The seed coat softens and ruptures at the
radicular end. When the cotyledons remain under the sol or
(z) The radicle pierces out of the seed coat, bends Just on the ground during germination of seed, it is
called hypogeal germination. It is because of the
Ettc downwards and grows into the soil.
(iv) The radicle forms the primary root, Lateral rapid growth of epicotyl that the plumule emerges
roots begin to emerge. Root hairs appear out of the soil. It is found in the seeds of gram,
in the region where elongation has ceased. pea, maize, mango, groundnut, etc.
Water and salts absorbed by the root hairs Various stages during the hypogeal germination
are passed on to the seedling. Meanwhile,
of maize - a monocotyledonous endospermic seet
the hypocotyl elongates and arches upwards and pea - a dicotyledonous non-endospermic seed
above the soil. The two cotyledons are within are summarized as follows :
the ruptured seed coat.
(w) The hypocotyl straightens, pulling the Hypogeal germination in maize (Zea mays
cotyledons into the air. The ruptured seed (Fig. 5.9)
coats may remain below the soil or are shed
above the soil. ) The grain absorbs water and swells. "ne
cotyledon absorbs food material stored in the
(vi) The hypocotyl becomes completely erect. The endosperm.
two cotyledons diverge to form the flat, green
cotyledonary leaves. The epicotyl elongates, (ii) The radicle pierces through the protective
bearing at its tip of the plumule. root sheath (coleorhiza). It grows downwaru
into the soil.
the tip of the epicotyl.
(vii) The young leaves unfold atand (iüi) The radicle develops into the primary ro
The cotyledons shrivel up are shed. with root hairs.
and persists
( )The primary root gives branches
plant. Such aroot (iw) The coleoptile elongates and pierces outaf
all through the lite of the
leavesnow
is called a tap root. The young the grain in the form of atube opposite
prepare food for the plant. direction to the coleorhiza.
Candid ICSE Biology
 PUUL E (iv) The epicotyl begins to elongate and forms a
Small loop. Root hairs appear in the region of
the radicle where elongation has ceased.
(0) The epicotyl elongates rapidly. The plumule
PLUMULE
COLEOPTLLE
located at its tip becomes free from the
cOLEOPTILE cotyledons by the straightening of the epicotyl
loop.
(vi) Young leaves appear and prepare food for
the plant. Seed coats and cotyledons remain
o RADICLE below the soil.
ADVENTfUS (vii) Primary root persists giving rise to a tap root
PRIMARY ROOTS system.
ROOT PRIMARY ROOT
PERISHES
(i) (v 5.3.3 Special type of germination (Vivipary,
Flg. 5.9: Hypogeal germination in maize
Fig. 5.11)
Epigeal Germination Hypogeal Germination
(p) Acluster of fibrous roots arise around the 1. Cotyledons come above thel 1. Cotyledons rermain below the
base of the primary root. These develop from soil. soil.

the base of the stem. The first leaf of the 2. Hypocotyl elongates. 2. Epicotyl elongates.

plumule pierces out of the coleoptile which The seeds of the plants growing along the
now forms a tube-like collar around its base.
sea-shore or in saline marshes show a special
(vi) More leaves appear in succession. Primary root type of germination called vivipary. In this type
perishes giving rise to a fibrous root system. of germination, the seed germinates inside the fruit
while it is still attached to the parent plant. A cub
Hypogeal germination in the seed of pea shaped radicle emerges out of the fruit. The lower part
Pisum sativum (ig. 5.10) of the radicle gets swollen. Finally the seedling gets
() The seed absorbs water and swells. detached from the parent plant and gets embedded
(ii) Food reserves in the cotyledons become in the muddy soil below. The radicle develops lateral
branches quickly to anchor the seedling.
soluble by the action of enzymes and pass in
the tips of the growing plumule and radicle. This type of germination is found in Rhizophora,
Ceriops, Avicennia, Heritiera, Sonneratia, etc.

PLUMULE IS WITHDRAWN FROM

STIPULES
BETWEEN THE COTYLEDONS
TESTA SPLITS AND -EPICOTYL BRANCH
RADICLE EMERGES -FRUIT
COTYLEDON,
STALK

RADICLE PRIMARY
TAP ROOT FRUIT

RADICLE -SEEDLING
(a)
-MUDDYSOIL
Fig. 5.10 : Hypogaal gemination in the seed of pea
(6)

( )The sed coat ruptures, the radicle elongates, Fig. 5.11: Viviparous germination in Rhizophora
emerges from the ruptured seed coat and (a) Germination while in fruit.
grows downwards into the soil. (b) Attached seedling with fleshy radicle.
(c) Detached seedling with lateral roots.

Structure and Geminaton o Seeds 69

 Key Points to
REMEMBER After the dormant
period is over, the seeds

provigderedmina
Afertilized and seedling, if
mature ovule is called seed. establish an independent
Aseed is covered by twO seed to
sufficient water, oxygen and optimum temperature.
coats (testa and
Contains reserve food and a miniature planttegmen), of all the
called Germination is the sum total processes which
embryo. helpin avwakeningthe dormant embryo, its growh so0
Embryo consists of one independent seedling.
(dicotyledonous) seed leaves(monocotyledonous)
or
called cotyledons andtwo
an to establish an
Germination of seedsrequires sufficient quantity of
embryonal axis. temperature.
The embryonal axis is differentiated into mesocoty!, oxygen and optimum
Germination of seeds is of two types i.e.
epicotyl, hypocoty, plumule and radicle.
The upper leafy part of the embrvonal axis is called
hypogeal germination. epigeal and
cotyledons rise
plumule which forms the future shoot system and lower In epigeal germination, the ground in
leaves due to
pointed part is called radicle that forms the future root the form of cotyledonary
found in castor, bean, etc.
rapid growth o
system. hypocotyl. It is
In hypogeal germination the cotyledons remain
Food is stored for the early germination of seeds either
in the cotyledons (exalbuminous) or in the endosperm the soil or just abOve the ground and the plumule beeneath
(albuminous or endospermic seeds). due to rapid growth of the epicotyl. It iis found in pea,
Seeds after shedding off from the parent plant, usually gram, maize, etc.
undergo a dormant period. During dormancy they may G Seeds of plants growing along sea-shore or in sali
not germinate even if provided with all the favourable marshes show a special type of germination caled
Conditions. vivipary e.g. Rhizophora and Heritiera.

KEY

1. Albuminous (Endospermic) seeds - seeds in which 10. Hilum -A scar on the seed which demarcates the point
the food is stored in endosperm. of attachment of seed with the stalk.
2. Coleoptile - A protective conical cap on the plumule of 11. Hypocotyl Portion of the embryonal axis betwen
maize grain. mesocotyl and radicle.
3. Coleorhiza -A protective sheath on the tip of radicle of 12. Hypogeal Germination - Germination, in which the
maize grain cotyledons remain beneath the soil or just above the
4. Dormancy - The phenomenon of failure of germination ground.
of seed even after providing most favourable conditions 13. Mesocotyl - Part of the embryonal axis where
is called dormancy. (Innate inhibition of germination) cotyledons are attached.
5. Embryo - Young or miniature plant present in the seed 14. Micropyle -A minute pore near the hilum through which
is called embryo. absorption of water and exchange of gases take placa.
6. Epicotyl - Portion of the embryonal axis between the 15. Optimum temperature - Temperature at which e
point of attachment of cotyledons and plumule. germination of seed is most rapid.
7. Epigeal germination - Germination, in which cotyledons 16. Plumule - Feathery or leafy upper end of embryond
emerge out of the soil and develop as cotyledonary axis that develops into shoot system.
leaves. 17. Radicle - The pointed lower end of embryonal axiS Ui
8. Funiculus - A small stalk with which the seed is develops into root system.
attached to the placenta. 18. Raphe - Aprominent ridge-like structure that represenis
a part of the stalk.
9 Germination - The sum total of all the processes by
which the dormant embryo of the seeds wakes up, 19. Seed - Fertilized and
mature ovule.
arows out of the seed coats and establishes itself as an 20. Tegmen - Inner, thin,
independent seedling.
membranous seed coat.
21. Testa -Outer, hard,
protective seed coat.

70 Candid ICSE Biology