Chapter-5
Morphology
of Flowering Plants
Syllabus (2023-24): Morphology of different parts of
flowering plants: root, stem, leaf, inflorescence, flower, fruit and seed.
Description of family Solanaceae
The
underground part of the flowering plant is the root
system while the portion above the ground forms the shoot system (Figure 5.1).
Difference between Monocots and Dicot
seeds
i) The endosperm plays an important role in supporting
embryonic growth by supplying nutrients, protecting the embryo and controlling
embryo growth by acting as a mechanical barrier during seed development and
germination.
ii) Generally dicot seeds lack endosperm
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Epicotyl: The epicotyl is the embryonic shoot located above the point of
attachment of the cotyledons. It is the part of the embryo that will develop
into the upper stem and eventually form the leaves and other aerial parts of
the plant. During germination, the epicotyl is the first part to emerge from
the soil. Hypocotyl: The hypocotyl is the region of the embryonic stem located below
the point of attachment of the cotyledons and above the radicle. It serves as
a transitional region between the epicotyl and the radicle. In some seeds,
the hypocotyl may elongate during germination to help push the cotyledons and
epicotyl above the soil surface. Radicle: The radicle is the embryonic root of the dicot seed. It is the
first part of the embryo to emerge during germination, and its primary
function is to develop into the root system of the plant. As the radicle
elongates, it anchors the seedling to the soil and starts absorbing water and
nutrients from the surrounding environment to support further growth. |
5.1.
Root
1.
In majority of the dicotyledonous plants, the direct
elongation of the radicle leads to the formation of primary root which grows
inside the soil.
2.
It bears lateral roots of several orders that are
referred to as secondary, tertiary, etc. roots.
3.
The primary roots and its branches constitute the tap
root system, as seen in the mustard plant (Figure 5.2a).
4.
In monocotyledonous plants, the primary root is short
lived and is replaced by a large number of roots.
5.
These roots originate from the base of the stem and
constitute the fibrous root system, as seen in the wheat plant (Figure 5.2b).
6.
In 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
(Figure 5.2c).
7.
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 reserve food material and synthesis of plant growth regulators.
5.1.1 Regions of the Root
1. The root is covered at the apex by
a thimble-like (cap like) structure called the root cap
(Figure 5.3).
Root
Cap: The root cap is a protective layer of cells found at the tip of the
root. Its primary function is to shield the delicate meristem cells behind it
as the root pushes through the soil.
2. It protects the tender apex (delicate,
actively growing tip of the root) of the root as it makes its way through the soil.
Region of elongation/Region
of meristematic activity
1.
A few millimetres above the root cap is the region of
meristematic activity.
2.
The cells of this region are very small, thin-walled
and with dense protoplasm.
3.
They divide repeatedly.
4.
The cells proximal (closer) 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.
Region of maturation
1. The cells of the elongation zone
gradually differentiate and mature. Hence, this zone, proximal to region of
elongation, is called the region of maturation.
2. From this 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
1. The stem is the ascending part of
the axis bearing branches, leaves, flowers and fruits.
2. It develops from the plumule of
the embryo of a germinating seed.
3. The stem bears nodes and
internodes.
4. The region of the stem where
leaves are born are called nodes while
internodes are the portions between two nodes.
5. The stem bears buds, which may be terminal or axillary.
i) Terminal buds, also known as
apical buds, are
located at the apex or tip of the stem. They are responsible for the primary
growth of the stem, determining its overall length and shape.
ii) Axillary buds have the potential to form branches or lateral
shoots, which can further develop into new stems, leaves, or flowers
6. Stem is generally green when young
and later often become woody and dark brown.
7. The main function of the stem is
spreading out branches bearing leaves, flowers and fruits. It conducts water,
minerals and photosynthates.
8. Some stems perform the function of storage of food, support,
protection and of vegetative propagation.
5.3 THE LEAF
1. The leaf is a lateral, generally
flattened structure borne on the stem.
2. It develops at the node and bears a bud in its axil.
3. The axillary bud later develops into a branch.
4. Leaves originate from shoot apical
meristems and are arranged in an acropetal order.
i) When
leaves are arranged in an acropetal order, it means that the younger or newly
formed leaves are located closer to the shoot apex or tip, while the older
leaves are positioned progressively further down the stem.
5. They are the most important
vegetative organs for photosynthesis.
6. A typical leaf consists of three
main parts: leaf base, petiole
and lamina (Figure 5.4 a).
Leaf Base:
1. The leaf is attached to the stem
by the leaf base and may bear two lateral small leaf like structures called stipules.
i) While not
all plants have stipules, when present, they serve various functions,
including:
Protection: Stipules
can provide protection to the young, developing leaves and buds. They can
shield these delicate structures from physical damage, herbivory, or harsh
environmental conditions.
2. 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:
1. The petiole help hold the blade to
light.
2. Long thin flexible petioles allow
leaf blades to flutter in wind, thereby cooling the leaf and bringing fresh air
to leaf surface.
Lamina:
1. The lamina or the leaf blade is
the green expanded part of the leaf with veins and veinlets. 2. There is, usually, a middle
prominent vein, which is known as the midrib.
3. Veins provide rigidity to the leaf
blade and act as channels of transport for water, minerals and food materials.
4. The shape, margin, apex, surface and extent of incision of lamina
varies in different leaves.
5.3.1 Venation
1. The arrangement of veins and the
veinlets in the lamina of leaf is termed as venation.
It is of two types:
a) Reticulate b) Parallel
a) Reticulate
1. When the veinlets form a network,
the venation is termed as reticulate (Figure 5.4
b).
b) Parallel
1. When the veins run parallel to
each other within a lamina, the venation is termed as parallel
(Figure 5.4 c).
2. Leaves of dicotyledonous plants generally possess reticulate venation,
while parallel venation is the characteristic of most monocotyledons.
5.3.2 Types of Leaves
Depending upon the lamina, leaves are
of two types:
a) Simple b) Compound
a) Simple
1.
A leaf is said to be simple, when its lamina is entire
or when incised, the incisions do not touch the midrib.
2. Identifying features of a simple leaf:-
i.
Presence of one or two spicule.
ii.
Base may be swollen called pulvinus.
Note:- If any of the above features are
not present then it should be a compound leaf.
b) Compound
1. When the incisions of the lamina
reach up to the midrib breaking it into a number of leaflets, the leaf is
called compound.
2. A 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.
3. The compound leaves may be of two
types (Figure 5.5).
a) Pinnately compound leaf b) Palmately
compound leaf
a) Pinnately compound leaf
1. 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.
b) Palmately compound leaf
1. 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
1. Phyllotaxy is the pattern of
arrangement of leaves on the stem or branch.
2. This is usually of three types – alternate, opposite and
whorled (Figure 5.6).
a) Alternate
1. In alternate type of phyllotaxy, a single
leaf arises at each node in alternate manner, as in china rose, mustard and sun
flower plants.
b) Opposite
1. In opposite type, a pair of leaves
arise at each node and lie opposite to each other as in Calotropis and guava
plants.
c) Whorled
1. If more than two leaves arise at a node and form a whorl, it is called
whorled, as in Alstonia.
1. A flower is a modified shoot
wherein the shoot apical meristem changes to floral meristem.
2. Internodes do not elongate and the
axis gets condensed.
3. The apex produces different kinds
of floral appendages laterally at successive nodes instead of leaves.
4. When a shoot tip transforms into a
flower, it is always solitary.
5. The arrangement
of flowers on the floral axis is termed as inflorescence.
6. Depending on whether the apex gets
developed into a flower or continues to grow, two major types of inflorescences
are defined –
A) Racemose B)
Cymose.
A) Racemose
1. In racemose type of inflorescences
the main axis continues to grow, the flowers are borne laterally in an
acropetal succession (Figure 5.7).
B) Cymose.
1. In cymose type of inflorescence
the main axis terminates in a flower, hence is limited in growth.
2. The flowers are borne in a
basipetal order (Figure 5.7).
5.5 THE FLOWER
1. The flower is the reproductive
unit in the angiosperms.
2. It is meant for sexual
reproduction.
3. A typical flower has four
different kinds of whorls arranged successively on the swollen end of the stalk
or pedicel, called thalamus or receptacle.
4. These are
a) calyx b) corolla c) androecium d)
gynoecium.
i.
Calyx and corolla are accessory
organs.
ii.
Androecium and gynoecium are reproductive
organs.
iii.
In some flowers like lily, the calyx and corolla are
not distinct and are termed as perianth.
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Sepal:
Each individual unit of the calyx is called a sepal. Sepals are typically
green and leaf-like, and they form the outermost part of the flower. Their
primary function is to protect the flower bud before it opens.
Calyx:
The calyx is the collective term for all the sepals of a flower. |
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The perianth is a collective
term for the outer parts of a flower that enclose and protect the
reproductive organs. |
5. On the basis of presence of
reproductive organs, it is of two types:
a) Bisexual b)
Unisexual
a) Bisexual
1. When a flower has both androecium and gynoecium, it is bisexual.
b) Unisexual
1. A flower having either only stamens or only carpels is unisexual.
6. In symmetry, the flower may be symmetrical or asymmetrical
Symmetry may be of two types:
a) Actinomorphic (radial
symmetry) b) Zygomorphic (bilateral symmetry)
a) Actinomorphic (radial
symmetry)
1. 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.
b) Zygomorphic (bilateral
symmetry)
1. When
it can be divided into two similar halves only in one particular vertical
plane, it is zygomorphic, e.g., pea, gulmohur, bean, Cassia.
c) Asymmetric flower
1. 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.
7. Floral
appendages
1. A flower may be trimerous, tetramerous
or pentamerous when the floral appendages are in multiple of 3, 4
or 5, respectively.
8. Flowers with bracts-reduced leaf
found at the base of the pedicel - are called bracteate
and those without bracts, ebracteate.
9. Based on the position of calyx,
corolla and androecium in respect of the ovary on thalamus, the flowers are
described as
a) Hypogynous b) Perigynous c) Epigynous
a) Hypogynous
1. 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.
b) Perigynous
1. 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.
c) Epigynous
1. 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
1. Each flower normally has four
floral whorls, viz., calyx, corolla, androecium and
gynoecium (Figure 5.10).
5.5.1.1 Calyx
1. The calyx is the outermost whorl
of the flower and the members are called sepals.
Sometimes there are
additional leaf like structures present below the calyx known as epicalyx.
Sepals: Generally, sepals are green, leaf
like and protect the flower in the bud stage.
2. The calyx may be gamosepalous (sepals fused) or polysepalous (sepals free).
5.5.1.2 Corolla
1. Corolla is composed of petals.
Petals:
I) Petals are usually brightly
coloured to attract insects for pollination.
2. Like calyx, corolla may also be gamopetalous (petals united) or polypetalous (petals free).
3. The shape and colour of corolla
vary greatly in plants.
4. Corolla may be tubular, bellshaped, funnel-shaped or wheel-shaped.
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Tubular
shaped |
Bell
shaped |
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Funnel
shaped |
Wheel
shaped |
5. 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.
i) The main types of aestivation are
a) Valvate b) Twisted c) Imbricate and d)
Vexillary
a) Valvate
1. 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.
b) Twisted
1. 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.
c) Imbricate
1. 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.
d) Vexillary
1. 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
1. Androecium is composed of stamens.
2. Each stamen which represents the
male reproductive organ consists of a stalk or a
filament and an anther.
i) Anther
Each anther is usually bilobed and each lobe
has two chambers, the pollen-sacs.
ii) Pollen sacs
The pollen
grains are produced in pollen-sacs.
3. A sterile stamen is called staminode (lacking the ability to produce
viable pollen).
4. Stamens of flower may be united
with other members such as petals or among themselves.
5. On the basis of attachment of
stamen with other members it may be of two types:
a) Epipetalous b)
Epiphyllous
a) Epipetalous
i) When stamens are attached to the
petals, they are epipetalous as in brinjal.
b) Epiphyllous
i) Epiphyllous when attached to the
perianth as in the flowers of lily.
6. The stamens in a flower may either
remain free (polyandrous) or may be united in varying degrees.
7. 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.
8. There may be a variation in the length of filaments within a flower,
as in Salvia and mustard.
5.5.1.4 Gynoecium
1. Gynoecium is the female
reproductive part of the flower and is made up of one or more carpels.
i) Carpel
1. A carpel consists of three parts
namely stigma, style
and ovary.
a) The stigma
is usually at the tip of the style and is the receptive surface for pollen
grains.
b) The style
connects the ovary to the stigma.
(a carpel is an individual unit of the female
reproductive organ, consisting of the stigma, style, and ovary. A pistil, on the other hand, represents the collective
term for all the carpels in a flower, whether they are separate or fused
together.)
c) Ovary
i) It is the enlarged basal part, on
which lies the elongated tube, the style.
ii) Each ovary bears one or more ovules attached to a flattened, cushion-like placenta.
2. On the basis of number of carpels,
these are of two types:
a) Apocarpous b)
Syncarpous
i) When more than one carpel is
present, they may be free (as in lotus and rose) and are called apocarpous.
b) Syncarpous
i) They are termed syncarpous when
carpels are fused, as in mustard and tomato.
3. Fertilisation
i) After fertilisation, the ovules
develop into seeds and the ovary matures into a fruit.
4. Placentation:
i) The arrangement of ovules within
the ovary is known as placentation.
ii) The placentation are of different
types namely:
a) Marginal b) Axile c)
Parietal d) Basal e) Central f) Free central (Figure 5.12).
a) Marginal
i) 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.
i) The "ventral suture" refers to the specific line
or seam along the ovary where the two carpels are joined.
ii) The "ridge" refers to a raised area or a
prominent elongated structure that forms along the ventral suture of the ovary.
This ridge provides the attachment site for the ovules, which are borne on this
ridge in two rows.
b) Axile
i) 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.
c) Parietal
i) 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.
d) Free central
i) When the ovules are borne on
central axis and septa are absent, as in Dianthus and Primrose the placentation
is called free central.
d) Basal
i) 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
1. The fruit is a characteristic
feature of the flowering plants.
2. It is a mature or ripened ovary,
developed after fertilisation.
3. If a fruit is formed without
fertilisation of the ovary, it is called a parthenocarpic
fruit.
(Some plant species naturally
possess the ability to develop parthenocarpic fruit without external
intervention. This can be due to genetic factors or hormonal regulations within
the plant itself. Examples of naturally parthenocarpic fruits include bananas,
pineapples, and some varieties of citrus fruits.)
4. Generally, the fruit consists of a
wall or pericarp
and seeds.
a) Pericarp
i) The pericarp may be dry or fleshy.
ii) When pericarp is thick and fleshy, it is
differentiated into the outer epicarp, the middle mesocarp and the inner
endocarp.
5.
In mango and coconut, the fruit is known as a drupe (Figure 5.13).
(Drupe is a type of fruit wherein, the pericarp or fruit
wall is differentiated into thin epicarp (skin) fleshy mesocarp and stony
endocarp. Hence, it is also called as stone fruit, e.g., Mango, Coconut, Peach,
Almond, Trapa etc.)
i) They develop from monocarpellary superior
ovaries and are one
seeded.
ii) 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
1. The ovules after fertilisation,
develop into seeds.
2. A seed is made up of a seed coat
and an embryo.
3. 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
1. The outermost covering of a seed
is the seed coat.
i) The seed coat has two layers, the outer testa and the inner
tegmen.
2. The hilum
is a scar on the seed coat through which the developing seeds were attached to
the fruit.
3. Above the hilum is a small pore
called the micropyle.
(The primary function of the micropyle is to provide a
passage for water absorption during seed imbibition, which is the process of
the seed taking in water to initiate germination. The micropyle acts as the
entry point for water to penetrate the seed coat and reach the embryo within.)
4. Embryo
i) Within the seed coat is the
embryo, consisting of an embryonal axis and two cotyledons.
ii) The cotyledons are often fleshy
and full of reserve food materials.
iii) At the two ends of the embryonal
axis are present the radicle and the plumule (Figure 5.14).
5. In some seeds such as castor the
endosperm formed as a result of double fertilisation,
is a food storing tissue and called endospermic seeds.
https://youtu.be/bUjVHUf4d1I?si=xXD09SkQ84dvk6mq (double fertilization)
(In angiosperms, the process of double fertilization involves
the fusion of two sperm cells with two different female gametes within the
ovule. One sperm cell fertilizes the egg cell, forming the diploid zygote,
which develops into the embryo. The other sperm cell fuses with the central
cell or the polar nuclei, resulting in the formation of the endosperm.
The endosperm is typically triploid, meaning it contains
three sets of chromosomes. This ploidy level is achieved through the fusion of
one sperm cell (haploid) with the two polar nuclei (each haploid) present in
the central cell of the ovule. The resulting endosperm nucleus contains a total
of three sets of chromosomes, one from the sperm cell and two from the polar
nuclei.)
6. In plants such as 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
1. Generally, monocotyledonous seeds
are endospermic but some as in orchids are non-endospermic.
2. In the seeds of cereals such as
maize the seed coat is membranous and generally fused with the fruit wall.
3. The endosperm is bulky and stores
food.
4. The outer covering of endosperm
separates the embryo by a proteinous layer
called aleurone layer.
5. The embryo is small and situated
in a groove at one end of the endosperm.
6. It consists of one large and
shield shaped cotyledon known as scutellum and a
short axis with a plumule and a radicle.
i) 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
1. Various morphological features are
used to describe a flowering plant.
2. The description has to be brief,
in a simple and scientific language and presented in a proper sequence.
3. The plant is described beginning with its habitat,
vegetative characters – roots, stem and leaves and then floral characters
inflorescence and flower parts.
4. After describing various parts of
plant, a floral diagram and a floral formula are presented.
5. The floral formula is represented by some symbols.
6. In the floral formula:
i) Br
stands for bracteate
ii) K
stands for calyx
iii) C
for corolla
iv) P
for perianth
v) A
for androecium
vi) G
for Gynoecium, G for superior ovary (hypogynous)
and 
for inferior ovary
(epigynous)
vii) ♂ for male
viii) ♀ for female,
ix)
for bisexual plants
x) ⊕ for actinomorphic (radial symmetry)
xi) 
for zygomorphic nature of flower (bilateral
symmetry).
7. Fusion is indicated by enclosing
the figure within bracket and adhesion by a line (___) drawn above the symbols
of the floral parts.
8. 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).
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If the dot on the floral diagram
is placed at the top, it indicates that the floral parts (such as sepals,
petals, stamens, and carpels) are attached to the apex or tip of the mother
axis (main stem). |
|
Explanation
of the Diagram
|
9. The position of the mother axis (main
stem) 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.
10. Floral formula also shows cohesion and adhesion within parts of
whorls and between whorls.
5.9 SOLANACEAE
1. 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).
2. Vegetative
Characters
i) Plants mostly herbs, shrubs and
rarely small trees
ii) Stem:
herbaceous rarely woody, aerial; erect, cylindrical, branched, solid or hollow,
hairy or glabrous (smooth or free from hair), underground stem in potato
(Solanum tuberosum)
iii) Leaves:
alternate, simple, rarely pinnately compound, exstipulate (lacks stipules) ;
venation reticulate
3. Floral
Characters
i) Inflorescence
: Solitary, axillary or cymose as in Solanum
ii) Flower:
bisexual, actinomorphic
iii) Calyx:
sepals five, united, persistent, valvate aestivation
iv) Corolla:
petals five, united; valvate aestivation
v) Androecium:
stamens five, epipetalous
vi) Gynoecium:
bicarpellary obligately placed, syncarpous; ovary superior, bilocular, placenta
swollen with many ovules, axile
vii) Fruits:
berry or capsule Seeds: many, endospermous
4. Floral
Formula: 
5. Economic
Importance
i) Many plants belonging to this family are source of food (tomato,
brinjal, potato), spice (chilli); medicine (belladonna, ashwagandha);
fumigatory (tobacco); ornamentals (petunia).
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Q. In a monocot seed, which of the following structures separates the embryo from the endosperm and also includes a shield-shaped cotyledon called the scutellum?
A) Coleoptile
B) Aleurone layer
C) Testa
D) Plumule
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Chapter 4: Animal Kingdom
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