This document provides information about sexual reproduction in flowering plants. It begins by describing flowers and their structures. It then discusses the male and female gametophytes - specifically pollen formation (microsporogenesis), pollen structure, and embryo sac formation (megaspore and megagametophyte development). It also describes the processes of pollination, fertilization, and seed and fruit development after fertilization. Key terms like anemophily, entomophily, autogamy and geitonogamy in relation to pollination are explained. The document thus provides a comprehensive overview of sexual reproduction from gamete formation to seed production in flowering plants.

1. SEXUAL
REPRODUCTION IN
FLOWERING
PLANTS
By: V. S. Malik

2. SEXUAL
REPRODUCTION
IN FLOWERING
PLANTS
By: V.S.Malik

3. FLOWERS ARE FASCINATING ORGANS OF ANGIOSPERMS
WHICH ARE SYMBOLIC OF BEAUTY, LOVE AND SERENITY. IT
IS A MODIFIED SHOOT BEARING SPOROPHYLL WITH
CONDENSED THALAMUS AND APPENDAGES, IN WHICH
INTERNODES HAVE BECOME CONDENSED TO BRING THE
NODES CLOSE TO ONE ANOTHER, AND THE LEAVES ARE
MODIFIED TO FORM FLORAL WHORLS THAT DIRECTLY OR
INDIRECTLY PARTICIPATE IN THE PROCESS OF
REPRODUCTION.

4. TYPICAL FLOWERING PLANT
 The plant tissues and structures
make up two broad systems:
the shoot system and the root
system.
 The shoot system is made up
primarily of leaves, stems,
and reproductive structures (e.g.,
flowers, fruits and seeds, etc.)
 The root system is made up of
roots, (primary, secondary or
tertiary roots etc.)
 Each of these structures has
characteristics that help it to
carry out its major functions.

5. TYPICAL FLOWER
 Pedicle: The stalk of a flower.
 Receptacle or Thalamus (Torus): : The
upper swollen portion of pedicle, where the
parts of the flower are attached.
 Sessile: When the pedicle is absent.
 Bracteolate: Presence of two small leaf like
structures on the pedicle of flower.
 Bracteate: Flower arising in the axil of a
bract.
 Ebracteate: When the bract is absent at the
base of a flower.
 Sepals (Whorl - Calyx): The outer parts of
the flower (often green and leaf-like) that
enclose a developing bud.

6. TYPICAL FLOWER
-Petals (Whorl - Corolla): The parts of a flower
that are often conspicuously colored.
-Stamens (Whorl - Androecium): The pollen
producing part of a flower, usually with a
slender filament supporting the anther.
-Anther: The part of the stamen where pollens
are produced.
-Pistil (Carpel and whorl of carpels is known
as gynoecium): The ovule producing part of a
flower. The ovary often supports a long style,
topped by a stigma. The mature ovary is a
fruit, and the mature ovule is a seed.
-Stigma: The part of the pistil where pollen
germinates.
-Ovary: The enlarged basal portion of the
pistil where ovules are produced.

7. FLOWERS
 Smallest flower- Wolffia microscopia
 Largest Flower- Rafflesia
 National flower of India- Lotus (Nelumbium)
 Complete flower- Contains all floral parts i.e. calyx, corolla,
androecium and gynoecium.
 Perfect flower or bisexual or hermaphrodite flower- Possesses both the
essential (reproductive) organs.
 Unisexual flower- Flower missing any of two reproductive organs. Male
or staminate flower- if carpels are absent, female or pistillate- if
stamens are absent and neuter- if both essential whorls are absent.
 Monoecious plants- Have both male and female flowers on the same
plant, e.g. Maize, Caster and Coconut.
 Dioecious plants- Male and female flowers on different plants, e.g.
Papaya, Mulberry and Date palm.

8. LIFE CYCLE OF AN ANGIOSPERM
Pre-fertilisation: Structure and events
Formation and development of pollen grains
STAMEN:- The pollen-producing reproductive
organ of a flower, consists of two parts (i)
Filament- long narrow stalk, (ii) Anther- upper
broader knob-like, bi-lobed, bithecous or
dithecous. Two anther lobes contain four
pollen sacs (micro-sporangia) in which pollen
grains are produced.

9. STRUCTURE OF MICROSPORANGIUM (POLLEN SAC)
 Microsporangium (pollen sac) is the structure
that give rise to male gametes or microspores
(pollen grains) in an angiosperm.
 It is circular in outline in transverse section
and is usually surrounded by four wall layers.
 Epidermis- It is a single layer and outermost
layer. The main function lies in the protection
of pollen.
 Endothecium- It is the layer that is present
beneath the epidermis and it helps in
thickening or provides thickening.
 Middle layers- It is made of further 2-3 layers.
 Tapetum- It is the innermost multinucleated
layer with dense cytoplasm. The main function
lies in nourishment. The cells of tapetum may
be multinucleate.
 The outer three layers are protective in
function. They also help in dispersal of pollens
by dehiscing themselves.

10. SPOROGENOUS TISSUE
 The centre of the microsporangium comprises of
compact sporogenous tissue.
 Sporogenous Tissue – It is a group of cells
which differentiates into microspore mother cell
or pollen mother cell.
 Each microspore mother cell undergoes meiosis
and gives rise to haploid microspore.
 The cycle by which a microspore is formed from
the microspore or pollen mother cell is known as
microsporogenesis (the process by which
extremely tiny spores are formed in the pollen
sacs of seed plants).
 As the anther develops it dries out and the
microspores separate from one another and form
into pollen grains.
 Eventually the developed pollen grains are
dispersed and help the plant in reproduction.

11. MICROSPOROGENESIS

12. STRUCTURE OF POLLEN GRAIN
 Each pollen grains has a two-
layered wall. The outer hard layer
called the exine is made up of
sporopollenin which is one of the
most resistant organic material
that enables them to resist high
temperature and strong acid and
alkali. No enzyme is yet known to
degrade sporopollenin.
 The region on exine where
sporopollenin is absent are called
the germ pores. It helps in the
formation of pollen tube.
 The inner layer is thin called as
intine. It is composed of cellulose
and pectin.
 A mature pollen grain contains
two cells ,the vegetative cell and
the generative cell.
 The vegetative cell is bigger, has
abundant food reserve and a large
irregular shaped nucleus.
 The generative cell is small and
floats in the cytoplasm of the
vegetative cell.
 In about 60% of angiosperms, pollen
grains are shed at this 2- celled
stage.
 In the remaining species, the
generative cell divides mitotically to
give rise to two male gametes before
pollen grains are shed (3 celled
stage).

13. MEGASPOROGENESIS
 Megasporogenesis: Due to the meiosis of a single
diploid mother cell, the haploid megaspore tetrad forms.
 Out of this, three disintegrates, and one sustains, which
later develops into the embryo sac.

14. MEGAGAMETOGENESIS
 Development of Female Gametophyte
 Functional megaspore is the first cell of the female gametophyte.
 The cell enlarges and undergoes three free nuclear mitotic divisions. The first
division produces two nucleated embryo sac. These two nuclei divide twice
forming four nucleate and then eight nucleate structure.
 One nucleus from each side moves to the middle of the embryo sac. They are
called polar nuclei.
 The remaining three nuclei form cells at the two ends, three celled egg
apparatus at the micropylar end and three antipodal cells at the chalazal end.
 The middle binucleate structure organises itself into a central cell.
 The female gametophyte in angiosperms is called the embryo sac. It is a 7-
celled and 8-nucleated structure.

15. DEVELOPMENT OF FEMALE GAMETOPHYTE

16. ANATROPOUS OVULE
 Anatropous ovule is the most
common type of ovules, which
occurs in more than 80% of
angiosperm families.
 The body of ovule is rotated by 180°
and micropyle comes near to the
funiculus.
 Chalaza and micropyle lie in the
straight line but hilum is at 90° to
micropyle.
 Thus, micropyle is near to funiculus.
 A ridge is also present in the ovule
as the body of ovule is fused with
the funiculus on one side.

17. POLLINATION
 Pollination is the act of transferring pollen grains from the male
anther of a flower to the female stigma.
 The goal of every living organism, including plants, is to create
offspring for the next generation. One of the ways that plants
can produce offspring is by making seeds.
 Seeds contain the genetic information to produce a new plant.

18. TYPES OF POLLINATION
 There are basically two types of pollination: Self-pollination and cross-
pollination.
 Self-Pollination: Pollen grains from the male part of the flower (anther) fall
directly on the stigma (female part) of the same flower and fertilisation occurs,
e.g. wheat, apricot, rice and peanut etc.
 Types of Self-Pollination: Self-pollination can be of two types. Autogamy and
Geitonogamy
 Autogamy It is a type of self-pollination where the transfer of pollen grains
from the anther to the stigma takes place within the same flower.

19. AUTOGAMY
CHASMOGAMOUS FLOWERS CLEISTOGAMOUS FLOWERS
Chasmogamous flowers are
commonly showy with open petals
encircling exposed reproductive
parts, to give a chance of cross-
pollination. e.g. Sunflower,
Hibiscus, Viola, beans, peas and
Commelina flowers .
Anther and stigma are not exposed but lie
close enough for transfer. Thus, the chances
of cross-pollination in cleistogamous flowers
are almost none. In addition, they barely
require a pollinating agent. e.g. Viola, Oxalis,
Commelina, Cardamine etc.

20. AUTOGAMY
 Autogamy is possible under some circumstances:
 (i) Anther and the stigma of the same flower should be
open.
 (ii) Anther-stigma synchronization; when the pollen is
released, stigma should be ready to receive it.
 (iii) Anther and stigma should be close enough.
 Autogamy is the closest form of inbreeding.
 Autogamy leads to homozygosity.
 Such species develop homozygous balance and do not
exhibit significant inbreeding depression.

21. GEITONOGAMY
 This type of self-pollination
occurs when transfer of
pollen grains from the male
part of the plant to the female
part of the plant takes place
in different flowers but of the
same plant. e.g. Maize
 Geitonogamy seems more of
a cross-pollination and
requires pollination agent but
since it occurs in the same
plant is called self-pollination.

22. CROSS POLLINATION (XENOGAMY)
 Cross-Pollination (also called xenogamy): This type of
pollination is more complex as here the transfer of pollen
grain occurs from the anther of one flower to the stigma
of a different flower.
 The movement of pollen grains in cross-pollination is
possible through pollinating agents.
 Pollinating agents can be anything like animals, insects,
winds and some other abiotic and biotic things.
 Generally, cross-pollination occurs in bright colour
flowers as their colour and odour attracts the insects like
bees. Xenogamy, leads to a new variety.
 Some of the cross-pollination plants are lavender,
strawberry, apple, dandelion etc.

23. CROSS POLLINATION
 Hydrophily- These flowers are pollinated by
water means. The flowers are often very small
and inconspicuous to other agents. They do not
have any fragrance or too much color on their
petals. The pollen is adapted to be able to float
in water. e.g. Hydrilla, Zostera, Vallisneria etc.
 Zoophily– The pollinating agents are animals
like human beings, bats, birds etc. The
zoophilous flowers have pollen that is designed
to stick on to the body of the animal so that they
can be easily carried from one flower to another.
e.g. Madar, Shimul, Kadam etc.
 Ornithophilous flowers– These flowers are
pollinated by birds. Very few flowers and birds
show this form of pollination. e.g. Bottle brush,
red coral tree and silk-cotton etc.

24. CROSS POLLINATION
 Anemophily– These flowers are pollinated by wind.
The flowers, are small and inconspicuous. Other
important features of flowers are that they are very
light so that they are easily carried by the wind, non-
sticky and sometimes winged. e.g. Poplar, beech,
alder, oak, chestnut, willow and elm trees, wheat,
maize, oats, rice and nettle etc.
 Entomophily– These flowers are pollinated by
insects. The flowers are often attractive to look at
with bright petals and are fragrant to attract the
insect visitors to them. They often have broad
stigmas or anthers to allow the insect to perch on it.
Many of the insect-pollinated flowers also secrete
nectar which attracts bees, butterflies or other
similar insects to the flowers. The pollen grains in
these flowers are often spiny or have extensions that
help them to stick on to the body of the insects. e.g.
Jasmine, Rafflesia, euphorbia, bougainvillea salvia,
fig, Viola, etc

25. POLLEN - PISTIL INTERACTION
 Pollen-pistil interactions:- All events
from pollen deposition on the
stigma until the entry of the pollen
tube into the ovule.
 It is a dynamic process which
involves pollen recognition by
stigma/pistil for compatible pollen
grains.
 Incompatible or sterile pollens are
rejected by the pistil and do not
allow to grow the pollen tube.

26. POLLEN - PISTIL INTERACTION
 Compatible pollens are encouraged for growth of pollen
tubes.
 Pollen tube grows through stigma and style to reach the
ovary.
 It then enters the ovule through micropyle and reaches the
synergids, guided by filiform apparatus.

27. ARTIFICIAL HYBRIDISATION
 Techniques involved to obtain desirable characters.
 Emasculation:- From the bisexual flowers, anthers are removed
using forceps before they dehisce.
 Bagging:- The emasculated flower is covered with a paper bag to
prevent contamination from unwanted flowers.
 On attaining maturity, matured pollens from desirable plant are
dusted on stigma of bagged flower and re-bagged for fruit
development.

28. DOUBLE FERTILISATION
 On reaching synergid, pollen tube release two male gametes into the
cytoplasm of synergid.
 Syngamy:- The event in which, one of the male gamete fuses with egg
nucleus to form a diploid cell ‘zygote’.
 Triple fusion:- The fusion of other male gamete with two polar nuclei at
the centre produces a triploid primary endosperm nucleus (PEN).
 Syngamy and triple fusion simultaneously is called ‘double fertilisation’.

29. POST FERTILISATION EVENTS
 (i) Development of endosperm from PEN.
 (ii) Development of embryo from zygote.
 (iii) Development of seeds from ovule.
 (iv) Development of fruit from the ovary.
1. Development of endosperm from PEN:- Successive nuclear
divisions in PEN give rise to free nuclei (water of tender
coconut in the centre). Subsequently, cell wall is formed and
endosperm becomes cellular.
Triploid cells of endosperm tissue are filled with reserve food
material to nourish the developing embryo.
Endosperm may be completely consumed by developing embryo
e.g. pea, beans or may persist in mature seed, e.g. coconut.

30. POST FERTILISATION EVENTS
 2. Development of embryo:- At the micropylar end of embryo sac
zygote divides mitotically to form proembryo globular embryo 
heart shaped embryo and finally forms mature embryo.
 By transverse division, large basal cell form suspensor. The apical
cells by vertical divisions give rise to plumule and hypocotyl.

31. STRUCTURE OF DICOTYLEDONOUS EMBRYO
 It consists of an embryonal axis and two
cotyledons.
 The portion of embryonal axis above the
level of cotyledon is called epicotyl,
which develops into plumule (future
shoot).
 The cylindrical portion below the level of
cotyledon is hypocotyl, which develops
into radicle or root tip (future root).
 Root tip is often covered with a root cap
(calyptra).
 E.g. mango, apple, radish, neem and rose
etc.

32. STRUCTURE OF MONOCOTYLEDONOUS EMBRYO
 It consists of one cotyledon, situated on
lateral side of embryonal axis and called
scutellum.
 The radicle and root cap are situated at the
lower end of embryonal axis in an
undifferentiated sheath called coleorhiza.
 The shoot apex and few leaf primordia are
enclosed in epicotyl region called
coleoptile.
 The portion of embryonal axis above the
level of attachment of scutellum is called
epicotyl.
 E.g. grass, banana, bamboo, palm etc.

33. SEED
 Seed is a fertilised ovule which is the
final product of sexual reproduction.
 It consists of seed coat(s) (1-2 in
number), an opening (micropyle),
testa (outer integument of seed
coat), tegman (inner integument of
seed coat), 1-2 cotyledon (rich in
reserve food material), and an
embryonal axis.
 Some time nucellus may persist
(called perisperm).
 With maturity, water content
decrease and it enters the state of
inactivity (dormancy).

34. FRUIT
 Ovary matures to form fruit and ovarian wall
develops into the wall of fruit called pericarp.
Fruits may be fleshy (orange and mango etc.)
or dry (mustard and groundnut etc.)
 False fruits:- The false fruits are formed from
the ripened ovary along with some other parts
of the flower such as the base or receptacle,
the perianth, thalamus, inflorescence, or
calyx.
 Some examples of false fruit are apple, pear,
gourd, cucumber, cashew-nut, jackfruit,
pineapple, banana and strawberry etc.
 Parthenocarpic fruits:- Fruits formed without
fertilisation. These fruits do not have seeds.
E.g. banana.

35. APOMIXIS (AGAMOSPERMY)
 Apomixis (agamospermy) is a form of asexual
reproduction that imitates sexual reproduction
by formation of embryo(s) and seeds without
meiosis and egg cell fertilisation.
 Apomictic seeds are exact genetic replicas of
the mother plant.
 Two ways of development of apomictic seeds:
 (i) Diploid egg is formed without meiosis and
develops into embryo without fertilisation.
 (ii) Some cells (diploid) of nucellus, start
dividing and without fertilisation and develop
into embryo. E.g. citrus fruits and mango.

36. POLYEMBRYONY
 Polyembryony is the phenomenon of two or more embryos developing
from a single fertilized egg. Due to the embryos resulting from the same
egg, the embryos are identical to one another, but are genetically diverse
from the parents.
 Cells of synergids, nucellus or integument etc. develop into embryo.
 Some times more than one embryo sac in an ovule are formed.
 When more than one egg in an embryo sac are formed.

37. Presentation by
V. S. Malik