UNIT 2

STRUCTURAL ORGANISATION IN PLANTS AND ANIMALS

 Angiosperms show such a large diversity
in external structure or morphology.
 Characterised by presence of roots,
stems, leaves, flowers and fruits
 Possible variations in different parts,
found as adaptations of the plants to their
environment,
 e.g., adaptions to various habitats, for
protection, climbing, storage, etc.
 5.1 ROOT
 Dicotyledonous plants, the direct
elongation of the radicle leads to the
formation of primary root.
 bears lateral roots of several orders
that are referred to as secondary,
tertiary roots.
 Monocotyledonous plants, the primary
root is short lived and is replaced by a
large number of roots.
 These roots originate from the base of
the stem and constitute the fibrous root
System.
 some plants, like grass, Monstera and
the banyan tree, roots arise from parts
of the plant other than the radicle and
are called adventitious roots.
 Main functions :
• Absorption of water and minerals from the soil
• Providing a proper anchorage to the plant Part
• Storing reserve food material
• Synthesis of plant growth regulators.

 Thimble-like structure called the root cap.

protects the tender apex
 Region of meristematic : thin-walled and with
dense protoplasm. They divide repeatedly.
 Region of elongation : cells proximal to this
region undergo rapid elongation and
 enlargement . (responsible for the growth of
the root in length)
 region of maturation :
 cells of the elongation zone gradually
differentiate and mature.
 some of the epidermal cells form very fine and
delicate, thread-like structures called root
 hairs. (root hairs absorb water and minerals
from the soil.)
 5.2 STEM
 stem is the ascending part of the axis bearing
branches, leaves, flowers and fruits.
 develops from the plumule of the embryo of
a germinating seed.
 The stem bears nodes and internodes.
 nodes : region of the stem where leaves are
born,
 internodes : portions between two nodes.
 The stem bears buds, may be terminal or
axillary.
 Stem is generally green when young and
later often become woody and dark brown.
 The main function of the stem is spreading
out branches bearing leaves, flowers and
fruits.
 It conducts water, minerals and
photosynthates.
 Some stems perform the function of storage
of food, support, protection and of
vegetative propagation.
 5.3 THE LEAF
 The leaf is a lateral, generally flattened
structure borne on the stem.
 It develops at the node and bears a bud in
its axil.
 The axillary bud later develops into a
branch.
 Leaves originate from shoot apical
meristems and are arranged in an
acropetal order.
 They are the most important vegetative
organs for photosynthesis.
 A typical leaf consists of three main
parts: leaf base, petiole and lamina.
 The leaf is attached to the stem by the
leaf base
 may bear two lateral small leaf like
structures called stipules.
 In monocotyledons, the leaf base expands
into a sheath covering the stem partially
or wholly.
 In some leguminous plants the
leafbase may become swollen, which
is called the pulvinus.
 Petiole help hold the blade to light.
 Long thin flexible petioles allow leaf
blades to flutter in wind,
 thereby cooling the leaf and bringing
fresh air to leaf surface.
 The lamina or the leaf blade is the Pulvinus Petiole
green expanded part of the leaf with
veins and veinlets.
 middle prominent vein, which is
known as the midrib.
 Veins provide rigidity to the leaf blade
 act as channels of transport for water,
minerals and food materials.
 The shape, margin, apex, surface and
extent of incision of lamina(V shaped
cuts of leaf blade) varies in different
leaves. Incision of lamina
 5.3.1 Venation
 The arrangement of veins and the veinlets in the lamina of
leaf is termed as venation.
 When the veinlets form a network, the venation is termed as
reticulate.
 When the veins run parallel to each other within a lamina,
the venation is termed as parallel.
 Leaves of dicotyledonous plants generally possess reticulate
venation,
 while parallel venation is the characteristic of most
monocotyledons.
 5.3.2 Types of Leaves
 A leaf is said to be simple, when its
lamina is entire or when incised,
 the incisions do not touch the midrib.
 When the incisions of the lamina reach
up to the midrib breaking it into a number
of leaflets, the leaf is called compound.
 bud is present in the axil of petiole in
both simple and compound leaves, but
not in the axil of leaflets of the compound
leaf.
 The compound leaves may be of two
types.
 In a pinnately compound leaf a number of
leaflets are present on a common axis, the
rachis, which represents the midrib of the
leaf as in neem.
 In palmately compound leaves, the
leaflets are attached at a common point,
 i.e., at the tip of petiole, as in silk cotton.
 5.3.3 Phyllotaxy
 Phyllotaxy is the pattern of
arrangement of leaves on the stem or
branch.
 This is usually of three types –
alternate, opposite and whorled .
 In alternate type of phyllotaxy, a
single leaf arises at each node in
alternate manner,
 in china rose, mustard and sun flower
plants.
 In opposite type, a pair of leaves arise
at each node and lie opposite to each
other as in Calotropis and guava
plants.
 If more than two leaves arise at a node
and form a whorl, it is called whorled,
as in Alstonia.
 5.4 THE INFLORESCENCE
 A flower is a modified shoot where in the
shoot apical meristem changes to floral
meristem.
 Internodes do not elongate and the axis
gets condensed.
 The apex produces different kinds of floral
appendages laterally at successive nodes
instead of leaves.
 When a shoot tip transforms into a flower,
it is always solitary.
 The arrangement of flowers on the floral
axis is termed as inflorescence.
 Depending on whether the apex gets
developed into a flower or continues to
grow,
 two major types of inflorescences are defined racemose and
cymose.
 In racemose type of inflorescences the main axis continues to
grow, the flowers are borne laterally in an acropetal succession
(oldest flowers at the base stem and the youngest flowers at the
top )
 In cymose type of inflorescence the main axis terminates in a
flower, hence is limited in growth.
 The flowers are borne in a basipetal order (oldest flowers at the
top stem and the youngest flowers at the base)
 5.5 THE FLOWER
 flower is the reproductive unit for sexual
reproduction in the angiosperms.
 typical flower has four different kinds of
whorls arranged successively on the
swollen end of the stalk or pedicel, called
thalamus or receptacle
 These are calyx, corolla, androecium and
gynoecium.
 Accessory : Calyx and corolla.
 Reproductive : androecium and gynoecium.
 flowers like lily, the calyx and corolla are
not distinct and are termed as perianth.
 Bisexual : flower has both androecium and
gynoecium.
 Unisexual : flower having either only
stamens or only carpels .
 In symmetry :
 flower may be actinomorphic (radial symmetry) or zygomorphic (bilateral
symmetry).
 Actinomorphic : When a flower can be divided into two equal radial halves in
any radial plane passing through the centre .
 e.g., mustard, datura, chilli.
 Zygomorphic : When it can be divided into two similar halves only in one
particular vertical plane.
 e.g., pea, gulmohur, bean, Cassia.
 flower is asymmetric (irregular) if it cannot be divided into two similar halves
by any vertical plane passing through the centre, as in canna.

a . Actinomorphic b . Zygomorphic c . Asymmetric

 A flower may be trimerous, tetramerous or pentamerous (floral appendages).
 Based on the position of calyx, corolla and androecium in respect of the ovary
on thalamus flowers are described as hypogynous, perigynous and epigynous.
 Hypogynous flower : gynoecium occupies the highest position while the other
parts are situated below it.
 The ovary in such flowers is said to be superior, e.g., mustard, china rose and
brinjal.
 Perigynous : gynoecium is situated in the centre and other parts of the flower are
located on the rim of the thalamus almost at the same level.
 The ovary here is said to be half inferior, e.g., plum, rose, peach.
 Epigynous : the margin of thalamus grows upward enclosing the ovary
completely and getting fused with it, the other parts of flower arise above the
ovary.
 the ovary is said to be inferior as in flowers of guava and cucumber, sunflower.
 5.5.1 Parts of a Flower
 four floral whorls, viz., calyx, corolla,
androecium and gynoecium
a. Calyx :
 outermost whorl of the flower called
sepals. Generally, sepals are green, leaf
like and protect the flower in the
 bud stage. The calyx may be
gamosepalous (sepals united) or
polysepalous (sepals free).
b. Corolla :
 Corolla is composed of petals. Petals are
usually brightly coloured to attract insects
for pollination.
 gamopetalous (petals united) or
polypetalous (petals free).
 The shape and colour of corolla vary
greatly in plants. Corolla may be tubular,
bell shaped, funnel-shaped or wheel-
shaped.
 Aestivation:

 The mode of arrangement of sepals or petals in

floral bud with respect to the other members of the
same whorl is known as aestivation.
 main types of aestivation are valvate, twisted,
imbricate and vexillary .
 Valvate : When sepals or petals in a whorl just
touch one another at the margin, without
overlapping, as in Calotropis.
 Twisted : If one margin of the appendage overlaps
that of the next one and so on as in china rose,
lady’s finger and cotton.
 Imbricate : If the margins of sepals or petals
overlap one another but not in any particular
direction as in Cassia and gulmohur.
 vexillary or papilionaceous : In pea and bean
flowers, there are five petals, the largest (standard)
overlaps the two lateral petals (wings) which in
turn overlap the two smallest anterior petals (keel).
c. Androecium
 Androecium is composed of stamens.
 consists of a stalk or a filament and an anther.
 Each anther is usually bilobed and each lobe
has two chambers, the pollen-sacs.
 pollen grains are produced in pollen-sacs. A
sterile stamen is called staminode.
 epipetalous : stamens are attached to the
petals (eg. brinjal)
 epiphyllous : when attached to the perianth
(eg. lily)
 polyandrous : stamens may remain free
 or may be united in varying degrees
 monoadelphous : stamens may be united into
one bunch (china rose)
 diadelphous : two bundles (pea),
 polyadelphous : more than two bundles
(citrus)
 may be a variation in the length of filaments
within a flower, as in Salvia and mustard.
D. Gynoecium
• Gynoecium is the female reproductive part of
the flower and is made up of one or more
carpels.
• A carpel consists of three parts namely
stigma, style and ovary.
• Ovary is the enlarged basal part, on which lies
the elongated tube, the style.
• The style connects the ovary to the stigma.
• The stigma is usually at the tip of the style
and is the receptive surface for pollen grains.
• Each ovary bears one or more
• ovules attached to a flattened, cushion-like
placenta.
• When more than one carpel is present, they
may be free (as in lotus and rose) and are
called apocarpous.
• They are termed syncarpous when carpels are
fused, as in mustard and tomato.
• After fertilisation, the ovules develop into
seeds and the ovary matures into a fruit.
• Placentation: The arrangement of ovules within
the ovary is known
• as placentation. The placentation are of different
types namely, marginal, axile, parietal, basal,
central and free central .
• In marginal placentation the placenta forms a
ridge along the ventral suture of the ovary and the
ovules are borne on this ridge forming two rows,
as in pea.
• When the placenta is axial and the ovules are
attached to it in a multilocular ovary, the
placentaion is said to be axile, as in china rose,
tomato and lemon.
• In parietal placentation, the ovules develop on the
inner wall of the ovary or on peripheral part.
• Ovary is one-chambered but it becomes two
chambered due to the formation of the false
septum, e.g., mustard and Argemone.
• When the ovules are borne on central axis and
• septa are absent, as in Dianthus and Primrose the
placentation is called free central.
• In basal placentation, the placenta develops at the
base of ovary and a single ovule is attached to it,
as in sunflower, marigold.
 5.6 THE FRUIT
• The fruit is a characteristic feature of the
flowering plants.
• It is a mature or ripened ovary, developed after
fertilisation.
• If a fruit is formed without fertilisation of the
ovary, it is called a parthenocarpic fruit.
• Generally, the fruit consists of a wall or pericarp
and seeds.
• The pericarp may be dry or fleshy.
• When pericarp is thick and fleshy, it is
differentiated into the outer epicarp, the middle
mesocarp and the inner endocarp.
• In mango and coconut, the fruit is known as a
drupe.
• They develop from monocarpellary superior
ovaries and are one seeded.
• In mango the pericarp is well differentiated into
an outer thin epicarp, a middle fleshy edible
mesocarp and an inner stony hard endocarp.
• In coconut which is also a drupe, the mesocarp
is fibrous.
 5.7 THE SEED
• The ovules after fertilisation, develop into seeds. A seed is
made up of a seed coat and an embryo.
• The embryo is made up of a radicle, an embryonal
axis and one or two cotyledons.
 Structure of a Dicotyledonous Seed
• Outermost covering of a seed is the seed coat.
• The seed coat has two layers, the outer testa and inner
tegmen.
• The hilum is a scar on the seed coat through which the
developing seeds were attached to the fruit.
• Above the hilum is a small pore called the micropyle.
• Seed consist embryo (embryonal axis and two cotyledons).
• The cotyledons are often fleshy and full of reserve food
materials.
• At the two ends of the embryonal axis are present the radicle
and the plumule.
• In some seeds such as castor the endosperm formed as a
result of double fertilisation, is a food storing tissue and
called endospermic seeds.
• In plants such as bean, gram and pea, the endosperm is not
present in mature seeds and such seeds are called non-
endospermous.
 Structure of Monocotyledonous Seed :
• Generally, monocotyledonous seeds are endospermic but some as in orchids are non-
endospermic.
• In the seeds of cereals such as maize the seed coat is membranous and generally
fused with the fruit wall.
• The endosperm is bulky and stores food.
• The outer covering of endosperm separates the embryo by a proteinous layer called
aleurone layer.
• The embryo is small and situated in a groove at one end of the endosperm.
• It consists of one large and shield shaped cotyledon known as scutellum and a short
axis with a plumule and a radicle. The plumule and radicle are enclosed in sheaths
which are called coleoptile and coleorhiza respectively
 5.8 SEMI-TECHNICAL DESCRIPTION OF A TYPICAL
FLOWERING PLANT
• Various morphological features are used
to describe a flowering plant.
• The description has to be brief, in a
simple and scientific language and
presented in a proper sequence.
• The plant is described beginning with its
habit, vegetative characters – roots, stem
and leaves and then floral characters
inflorescence and flower parts.
• After describing various parts of plant, a
floral diagram and a floral formula are
presented.
• The floral formula is represented by
some symbols.
• In the floral formula, Br stands for
bracteate , K stands for calyx , C for
corolla, P for perianth, A for androecium
and G for Gynoecium, G for superior
ovary and G for inferior ovary, ♂ for
male, ♀ for female, for bisexual
plants, ⊕ for actinomorphic
• % for zygomorphic nature of flower.
• Fusion is indicated by enclosing the
figure within bracket and adhesion by a
line drawn above the symbols of the
floral parts.
• A floral diagram provides information
about the number of parts of a flower,
their arrangement and the relation they
have with one another.
• The position of the mother axis with
respect to the flower is represented by a
dot on the top of the floral diagram.
• Calyx, corolla, androecium and
gynoecium are drawn in successive
whorls, calyx being the outermost and
the gynoecium being in the centre.
• Floral formula also shows cohesion and
adhesion within parts of whorls and
between whorls.
• The floral diagram and floral formula in
Figure 5.16 represents the mustard plant
(Family: Brassicaceae).
 Floral Formula :
Brassicaceae
The floral formula succinctly represents the
structure of Brassicaceae flowers as:

K₂+₂ C₄ A₂+₄ G(₂)

 Breaking it down:
K₂+₂: Four sepals arranged in two pairs (calyx)
C₄: Four free petals (corolla), arranged in a
cruciform (cross-shaped) pattern
A₂+₄: Six stamens in total—two shorter outer
stamens plus four longer inner stamens
(tetradynamous)
G(₂): Two fused carpels forming a syncarpous
(unicarpellate) gynoecium with a superior ovary
Some descriptions may include additional
symbols for symmetry:
⊕ for actinomorphic (radial symmetry),and for
bisexual flowers
Examples : Mustard: Brassica campestris ,Radish
Cauliflower, Cabbage, Turnip ,
Candytuft , Black mustard: Brassica nigra
 Malvaceae
 Floral Formula: Malvaceae

K(5) C5 A(∞) G(5)

 Breakdown:
– Flower is bisexual (has both
stamens and carpels)
K(5) – 5 fused sepals (gamosepalous
calyx)
C5 – 5 free petals (polypetalous corolla)
A(∞) – Numerous stamens,
monadelphous (fused into a staminal
tube around the gynoecium)
G(5) – 5 fused carpels (syncarpous),
superior ovary
Examples : balsa (Ochroma pyramidale)
baobab (genus Adansonia)
bombax cotton (genus Bombax)
bottle tree (genus Brachychiton)
cacao (Theobroma cacao)
 Solanaceae
 Floral Formula: Solanaceae

K(5) C(5) A5 G(2)

 Explanation:
– Bisexual flower (both stamens
and carpels are present)
K(5) – 5 fused sepals (gamosepalous)
C(5) – 5 fused petals (gamopetalous),
usually actinomorphic (radial
symmetry)
A5 – 5 free stamens, usually
epipetalous (attached to the corolla)
G(2) – 2 fused carpels, forming a
bicarpellary syncarpous gynoecium
with a superior ovary
Examples : Brugmansia arborea
Cestrum aurentiacum
 Fabaceae
 Floral Formula: Fabaceae

K(5) C1+2+(2) A(9)+1 G1

 Breakdown:
— Bisexual flower
K(5) — 5 fused sepals (gamosepalous calyx)
C1+2+(2) — 5 petals arranged zygomorphically:
1 large posterior standard
2 lateral wings
2 fused lower keel petals
A(9)+1 — 10 stamens; 9 fused (diadelphous) + 1
free
G1 — Monocarpellary, superior ovary (one carpel)
Symmetry:
The flower is zygomorphic (bilaterally
symmetrical).
Examples : Acacia (genus Acacia)
alfalfa (Medicago sativa)
almendro (Dipteryx oleifera)
bean (genus Phaseolus) common bean (P. vulgaris)
green bean (P. vulgaris) lima bean (P. lunatus)
The family Leguminosae is divided into three subfamilies, each with a slightly
different floral formula.

Family : Leguminosae (Fabaceae)

1. Papilionoideae 2. Caesalpinioideae 3. Mimosoideae

e.g., pea, bean e.g., Cassia, Gulmohar e.g., Acacia, Mimosa

1. Papilionoideae (e.g., pea, bean)
 Floral formula:

K(5) C1+2+(2) A(9)+1 or A(10) G1

 Explanation:
— Bisexual flower (both male and
female parts)
K(5) — 5 fused sepals (calyx)
C1+2+(2) — Corolla has 5 petals:
1 large standard, 2 lateral wings, and 2 lower
keel petals fused together (papilionaceous)
A(9)+1 — 10 stamens: 9 fused (diadelphous
condition), 1 free (sometimes all 10 fused:
A(10))
G1 — One superior ovary, monocarpellary
(single carpel)
2. Caesalpinioideae (e.g., Cassia,
Gulmohar)

 Floral formula:

K5 C5 A10 G1

 Explanation:

K5 — 5 free sepals
C5 — 5 free petals (not papilionaceous;
petals unequal)
A10 — 10 stamens (sometimes some are
sterile or unequal in size)
G1 — Single carpel (monocarpellary),
superior ovary
3. Mimosoideae (e.g., Acacia,
Mimosa)

 Floral formula:

K(5) C(5) A∞ G1

 Explanation:

K(5) — 5 fused sepals

C(5) — 5 fused petals
A∞ — Numerous stamens, often showy
and long
G1 — One superior ovary