This message is written so tht the website takes this as a document different from the original

UNIT 2
STRUCTURAL ORGANISATION IN
PLANTS AND ANIMALS

Chapter 5 Morphology The description of the diverse forms of life on earth was made only by
of Flowering Plants observation – through naked eyes or later through magnifying lenses
and microscopes. This description is mainly of gross structural features,
Chapter 6 both external and internal. In addition, observable and perceivable
Anatomy of Flowering living phenomena were also recorded as part of this description. Before
Plants experimental biology or more specifically, physiology, was established
as a part of biology, naturalists described only biology. Hence, biology
Chapter 7 remained as a natural history for a long time. The description, by itself,
Structural Organisation in was amazing in terms of detail. While the initial reaction of a student
Animals could be boredom, one should keep in mind that the detailed description,
was utilised in the later day reductionist biology where living processes
drew more attention from scientists than the description of life forms
and their structure. Hence, this description became meaningful and
helpful in framing research questions in physiology or evolutionary
biology. In the following chapters of this unit, the structural organisation
of plants and animals, including the structural basis of physiologial or
behavioural phenomena, is described. For convenience, this description
of morphological and anatomical features is presented separately for
plants and animals.

2024-25
 KATHERINE ESAU was born in Ukraine in 1898. She studied
agriculture in Russia and Germany and received her doctorate
in 1931 in United States. She reported in her early publications
that the curly top virus spreads through a plant via the food-
conducting or phloem tissue. Dr Esau’s Plant Anatomy published in
1954 took a dynamic, developmental approach designed to
enhance one’s understanding of plant structure and an
enormous impact worldwide, literally bringing about a revival
of the discipline. The Anatomy of Seed Plants by Katherine Esau was
published in 1960. It was referred to as Webster’s of plant
biology – it is encyclopediac. In 1957 she was elected to the
National Academy of Sciences, becoming the sixth woman to
receive that honour. In addition to this prestigious award, she
received the National Medal of Science from President George
Bush in 1989.
When Katherine Esau died in the year 1997, Peter Raven,
director of Anatomy and Morphology, Missouri Botanical
Katherine Esau Garden, remembered that she ‘absolutely dominated’ the field
(1898 – 1997) of plant biology even at the age of 99.

2024-25
 CHAPTER 5
MORPHOLOGY OF FLOWERING PLANTS
5.1 The Root The wide range in the structure of higher plants will never fail to fascinate
us. Even though the angiosperms show such a large diversity in external
5.2 The Stem
structure or morphology, they are all characterised by presence of roots,
5.3 The Leaf stems, leaves, flowers and fruits.
In chapters 2 and 3, we talked about classification of plants based
5.4 The Inflorescence
on morphological and other characteristics. For any successful attempt
5.5 The Flower at classification and at understanding any higher plant (or for that
matter any living organism) we need to know standard technical terms
5.6 The Fruit
and standard definitions. We also need to know about the possible
5.7 The Seed variations in different parts, found as adaptations of the plants to their
environment, e.g., adaptions to various habitats, for protection,
5.8 Semi-technical
climbing, storage, etc.
Description of a
If you pull out any weed you will see that all of them have roots, stems
Typical Flowering
and leaves. They may be bearing flowers and fruits. The underground
Plant part of the flowering plant is the root system while the portion above the
5.9 Description of ground forms the shoot system (Figure 5.1).
Some Important
Families 5.1 THE ROOT

In majority of the dicotyledonous plants, the direct elongation of the radicle

leads to the formation of primary root which grows inside the soil. It
bears lateral roots of several orders that are referred to as secondary, tertiary,
etc. roots. The primary roots and its branches constitute the

2024-25
58 BIOLOGY

tap root system, as seen in the mustard plant

Flower
(Figure 5.2a). In monocotyledonous plants,
the primary root is short lived and is
replaced by a large number of roots.
Fruit
These roots originate from the base of the
Stem stem and constitute the fibrous root
Leaf Shoot system, as seen in the wheat plant (Figure
system
5.2b). In some plants, like grass,
Monstera and the banyan tree, roots arise
Node Internode from parts of the plant other than the
{ Bud
radicle and are called adventitious roots
(Figure 5.2c). The main functions of the
root system are absorption of water and
minerals from the soil, providing a proper
anchorage to the plant parts, storing
Primary
root reserve food material and synthesis of
Root
Secondary system plant growth regulators.
root

Figure 5.1 Parts of a flowering plant

root

Fibrous roots Adventitious roots

(a) (b) (c)

Figure 5.2 Different types of roots : (a) Tap (b) Fibrous (c) Adventitious

2024-25
 MORPHOLOGY OF FLOWERING PLANTS 59

5.1.1 Regions of the Root

The root is covered at the apex by a thimble-like
structure called the root cap (Figure 5.3). It
protects the tender apex of the root as it makes
its way through the soil. A few millimetres above
the root cap is the region of meristematic
activity. The cells of this region are very small,
thin-walled and with dense protoplasm. They
divide repeatedly. The cells proximal to this
region undergo rapid elongation and
enlargement and are responsible for the growth
of the root in length. This region is called the
region of elongation. The cells of the elongation
zone gradually differentiate and mature. Hence,
this zone, proximal to region of elongation, is
called the region of maturation. From this
Figure 5.3 The regions of the root-tip
region some of the epidermal cells form very fine
and delicate, thread-like structures called root
hairs. These root hairs absorb water and
minerals from the soil.

5.2 THE STEM

What are the features that distinguish a stem from a root? The stem is the
ascending part of the axis bearing branches, leaves, flowers and fruits. It
develops from the plumule of the embryo of a germinating seed. The stem
bears nodes and internodes. The region of the stem where leaves are
born are called nodes while internodes are the portions between two nodes.
The stem bears buds, which 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.

2024-25
 60 BIOLOGY

A typical leaf consists of three main parts: leaf

base, petiole and lamina (Figure 5.4 a). The leaf is
attached to the stem by the leaf base and 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. The petiole help
(a) 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 green expanded part of
the leaf with veins and veinlets. There is, usually,
a middle prominent vein, which is known as the
midrib. Veins provide rigidity to the leaf blade and act
as channels of transport for water, minerals and
food materials. The shape, margin, apex, surface and
extent of incision of lamina varies in different
leaves.

5.3.1 Venation
The arrangement of veins and the veinlets in the
lamina of leaf is termed as venation. When the
(b) (c) veinlets form a network, the venation is termed as
reticulate (Figure 5.4 b). When the veins run
Figure 5.4 Structure of a leaf :
(a) Parts of a leaf parallel to each other within a lamina, the venation
(b) Reticulate venation is termed as parallel (Figure 5.4 c). Leaves of
(c) Parallel venation 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. A bud is present in
the axil of petiole in both simple and compound
(a) Neem leaves, but not in the axil of leaflets of the compound
Figure 5.5 Compound leaves : leaf.
(a) pinnately compound leaf The compound leaves may be of two types
(b) palmately compound leaf (Figure 5.5). In a pinnately compound leaf a

2024-25
 MORPHOLOGY OF FLOWERING PLANTS 61

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 (Figure 5.6). In alternate type of
phyllotaxy, a single leaf arises at each node
in alternate manner, as in china rose,
mustard and sun flower plants. In opposite
(c) Alstonia
type, a pair of leaves arise at each node and
lie opposite to each other as in Calotropis and Figure 5.6 Different types of phyllotaxy :
(a) Alternate (b) Opposite
guava plants. If more than two leaves arise
(c) Whorled
at a node and form a whorl, it is called
whorled, as in Alstonia.

5.4 THE INFLORESCENCE

A flower is a modified shoot wherein 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 (Figure 5.7).
In cymose type of inflorescence the main
axis terminates in a flower, hence is limited
in growth.The flowers are borne in a basipetal Figure 5.7 Racemose inflorescence
order (Figure 5.7).

2024-25
62 BIOLOGY

5.5 THE FLOWER

The flower is the reproductive unit in the
angiosperms. It is meant for sexual reproduction.
A 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. Calyx and corolla are accessory
organs, while androecium and gynoecium are
Figure 5.8 Cymose inflorescence reproductive organs. In some flowers like lily, the
calyx and corolla are not distinct and are termed
as perianth. When a flower has both androecium and gynoecium, it is
bisexual. A flower having either only stamens or only carpels is
unisexual.
In symmetry, the flower may be actinomorphic (radial symmetry) or
zygomorphic (bilateral symmetry). When a flower can be divided into
two equal radial halves in any radial plane passing through the centre, it
is said to be actinomorphic, e.g., mustard, datura, chilli. When it can be
divided into two similar halves only in one particular vertical plane, it is
zygomorphic, e.g., pea, gulmohur, bean, Cassia. A 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 flower may be trimerous, tetramerous or pentamerous when the floral
appendages are in multiple of 3, 4 or 5, respectively. Flowers with
bracts-reduced leaf found at the base of the pedicel - are called
bracteate and those without bracts, ebracteate.

(a) (b) (c) (d)

Figure 5.9 Position of floral parts on thalamus : (a) Hypogynous (b) and (c)
Perigynous (d) Epigynous

2024-25
 MORPHOLOGY OF FLOWERING PLANTS 63

Based on the position of calyx, corolla and androecium in respect of

the ovary on thalamus, the flowers are described as hypogynous,
perigynous and epigynous (Figure 5.9). In the hypogynous flower the
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. If 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, it is called perigynous. The ovary here is said to be half
inferior, e.g., plum, rose, peach. In epigynous flowers, the margin of thalamus
grows upward enclosing the ovary completely and getting fused with it,
the other parts of flower arise above the ovary. Hence, the ovary is said to be
inferior as in flowers of guava and cucumber, and the ray florets of
sunflower.

5.5.1 Parts of a Flower

Each flower normally has four floral whorls, viz., calyx, corolla,
androecium and gynoecium (Figure 5.10).

5.5.1.1 Calyx
The calyx is the outermost whorl of the flower and the members are 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).

5.5.1.2 Corolla
Corolla is composed of petals. Petals are usually brightly coloured to
attract insects for pollination. Like calyx, corolla may also be
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. The main types of aestivation are valvate, twisted, imbricate

Androecium

Figure 5.10 Parts of a flower

2024-25
64 BIOLOGY

(a) (b) (c) (d)

Figure 5.11 Types of aestivation in corolla : (a) Valvate (b) Twisted (c) Imbricate (d) Vexillary

and vexillary (Figure 5.11). When sepals or petals in a whorl just touch
one another at the margin, without overlapping, as in Calotropis, it is
said to be valvate. If one margin of the appendage overlaps that of the
next one and so on as in china rose, lady’s finger and cotton, it is called
twisted. If the margins of sepals or petals overlap one another but not in
any particular direction as in Cassia and gulmohur, the aestivation is
called imbricate. 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); this type of aestivation is known
as vexillary or papilionaceous.

5.5.1.3 Androecium
Androecium is composed of stamens. Each stamen which represents the
male reproductive organ consists of a stalk or a filament and an anther.
Each anther is usually bilobed and each lobe has two chambers, the
pollen-sacs. The pollen grains are produced in pollen-sacs. A sterile stamen
is called staminode.
Stamens of flower may be united with other members such as petals
or among themselves. When stamens are attached to the petals, they are
epipetalous as in brinjal, or epiphyllous when attached to the perianth as in
the flowers of lily. The stamens in a flower may either remain free
(polyandrous) or may be united in varying degrees. The stamens may be
united into one bunch or one bundle (monoadelphous) as in china rose, or
two bundles (diadelphous) as in pea, or into more than two bundles
(polyadelphous) as in citrus. There may be a variation in the length of
filaments within a flower, as in Salvia and mustard.

2024-25
 MORPHOLOGY OF FLOWERING PLANTS 65

5.5.1.4 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 (a)
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
(b)
placentation. The placentation are of different types namely,
marginal, axile, parietal, basal, central and free central (Figure 5.12).
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
(c)
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.
(d)
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.
(e)
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 Figure 5.12 Types of
is differentiated into the outer epicarp, the middle mesocarp and placentation :
(a) Marginal
the inner endocarp. (b) Axile
In mango and coconut, the fruit is known as a drupe (Figure (c) Parietal
(d) Free central
5.13). They develop from monocarpellary superior ovaries and are
(e) Basal
one seeded. In mango the pericarp is well differentiated into an

2024-25
 66 BIOLOGY

(a) (b)

Figure 5.13 Parts of a fruit : (a) Mango (b) Coconut

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 (as in wheat, maize) or two cotyledons (as in gram and pea).

5.7.1 Structure of a Dicotyledonous Seed

The outermost covering of a seed is the seed coat. The seed coat has two
layers, the outer testa and the 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
Seed coat micropyle. Within the seed coat is the embryo,
Cotyledon
consisting of an embryonal axis and two
Plumule
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 (Figure 5.14). In some seeds such
Hilum as castor the endosperm formed as a result of
Radicle double fertilisation, is a food storing tissue and
Micropyle
called endospermic seeds. In plants such as
Figure 5.14 Structure of dicotyledonous seed
bean, gram and pea, the endosperm is not
present in mature seeds and such seeds are
called non-endospermous.

5.7.2 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

2024-25
 MORPHOLOGY OF FLOWERING PLANTS 67

Seed coat & fruit-wall Endosperm

Aleurone layer
Scutellum

Coleoptile
Endosperm
Plumule

Embryo
Radicle
Coleorhiza

Figure 5.15 Structure of a monocotyledonous seed

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 (Figure 5.15).

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  K2+2 C4 A2+4 G(2)
superior ovary and G for inferior ovary, for male, for
Figure 5.16 Floral diagram with
female, for bisexual plants,  for actinomorphic floral formula

2024-25
68 BIOLOGY

and 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 (Figure 5.16). 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).

5.9 SOLANACEAE

It is a large family, commonly called as the ‘potato family’. It is widely

distributed in tropics, subtropics and even temperate zones (Figure 5.17).
Vegetative Characters
Plants mostly herbs, shrubs and rarely small trees
Stem: herbaceous rarely woody, aerial; erect, cylindrical, branched, solid or
hollow, hairy or glabrous, underground stem in potato (Solanum
tuberosum)
Leaves: alternate, simple, rarely pinnately compound, exstipulate;
venation reticulate

(b) (d)
(c)

(a)
(e) (f)

Figure 5.17 Solanum nigrum (makoi) plant : (a) Flowering twig (b) Flower
(c) L.S. of flower (d) Stamens (e) Carpel (f) Floral diagram

2024-25
 MORPHOLOGY OF FLOWERING PLANTS 69

Floral Characters
Inflorescence : Solitary, axillary or cymose as in Solanum
Flower: bisexual, actinomorphic
Calyx: sepals five, united, persistent, valvate aestivation Corolla:
petals five, united; valvate aestivation Androecium: stamens
five, epipetalous
Gynoecium: bicarpellary obligately placed, syncarpous; ovary superior,
bilocular, placenta swollen with many ovules, axile
Fruits: berry or capsule
Seeds: many, endospermous Floral
Formula:  Economic
Importance
Many plants belonging to this family are source of food (tomato, brinjal,
potato), spice (chilli); medicine (belladonna, ashwagandha); fumigatory
(tobacco); ornamentals (petunia).

SUMMARY

Flowering plants exhibit enormous variation in shape, size, structure,

mode of nutrition, life span, habit and habitat. They have well developed
root and shoot systems. Root system is either tap root or fibrous. Generally,
dicotyledonous plants have tap roots while monocotyledonous plants have
fibrous roots. The roots in some plants get modified for storage of food,
mechanical support and respiration. The shoot system is differentiated
into stem, leaves, flowers and fruits. The morphological features of stems
like the presence of nodes and internodes, multicellular hair and positively
phototropic nature help to differentiate the stems from roots. Leaf is a
lateral outgrowth of stem developed exogeneously at the node. These are
green in colour to perform the function of photosynthesis. Leaves exhibit
marked variations in their shape, size, margin, apex and extent of incisions
of leaf blade (lamina).
The flower is a modified shoot, meant for sexual reproduction. The
flowers are arranged in different types of inflorescences. They exhibit
enormous variation in structure, symmetry, position of ovary in relation
to other parts, arrangement of petals, sepals, ovules etc. After fertilisation,
the ovary is modified into fruits and ovules into seeds. Seeds either may
be monocotyledonous or dicotyledonous. They vary in shape, size and
period of viability. The floral characteristics form the basis of classification

2024-25
70 BIOLOGY

and identification of flowering plants. This can be illustrated through semi-

technical descriptions of families. Hence, a flowering plant is described in
a definite sequence by using scientific terms. The floral features are
represented in the summarised form as floral diagrams and floral formula.

EXERCISES

1. How is a pinnately compound leaf different from a palmately compound

leaf?
2. Explain with suitable examples the different types of phyllotaxy.
3. Define the following terms:
(a) aestivation (b) placentation (c) actinomorphic
(d) zygomorphic (e) superior ovary (f) perigynous flower
(g) epipetalous stamen
4. Differentiate between
(a) Racemose and cymose inflorescence
(b) Apocarpous and syncarpous ovary
5. Draw the labelled diagram of the following:
(i) gram seed (ii) V.S. of maize seed
6. Take one flower of the family Solanaceae and write its semi-technical
description. Also draw their floral diagram.

7. Describe the various types of placentations found in flowering plants.

8. What is a flower? Describe the parts of a typical angiosperm flower.
9. Define the term inflorescence. Explain the basis for the different types
inflorescence in flowering plants.
10. Describe the arrangement of floral members in relation to their
insertion on thalamus.

2024-25