This document summarizes sexual reproduction in flowering plants. It discusses pollination, which is the transfer of pollen grains from the anther to the stigma, allowing the transfer of gametes. There are three main types of pollination based on the source of pollen: autogamy, geitonogamy, and xenogamy. The document also describes the different agents of pollination, including wind, water, insects, birds and bats. Flowers have adapted for different pollination methods, such as wind-pollinated flowers being small and dry. The process of double fertilization is also summarized, where one sperm cell fuses with the egg to form a zygote, and another sperm fuses

1. Sexual Reproduction in
Flowering Plants
Part - III
Presented by:
ShashankTripathi

2. Gamete Transfer: Pollination
• Transfer of Gametes in Angiosperms and Gymnosperms take place
with the transfer of pollen grains from the anther to stigma of the
flower by the process called Pollination.
• Pollination can be defined as the transfer of Pollen grains from the
anther to the stigma of flower.
• Animals/insects that are involve in the pollination are called
“Pollinators”.
• Pollination by animals is an accidental process but plants have a proper
mechanism for the process.

3. Types of Pollination
On the basis of Source of Pollen-
• Autogamy: Transfer of pollen grains from
the anther of a flower to the stigma of the
flower of same plant or the another flower of
same plant. E.g., Mirabilis jalapa
• Geitonogamy: If transfer of pollen grains
takes place from the anther of a flower to the
stigma of the flower borne on same plant. It
is genetically Self Pollination but. E.g.,
Cucurbita
• Xenogamy (Cross Pollination): Transfer of
pollen grains from the anther of a flower to
the stigma of the flower of any other plant of
same species. E,g., Carica papaya, Zea maize
Pollination
Autogamy Geitonogamy Xenogamy
Source of
Pollen
Self- Pollination Cross- Pollination
Allogamy

4. Types of Pollination
A.---- Autogamy
B.---- Geitonogamy
C.---- Xenogamy

5. Agents of Pollination:
• The agents responsible for
pollination in angiosperms have been
grouped into categories as shown in
flow chart.
• Animals/insects that are involve in
the pollination are called
“Pollinators”.
• Pollination by animals is an
accidental process but plants have a
proper mechanism for the process.
Agents of
Pollination
Abiotic
Wind
Water
Biotic
Insects
Birds
Bats
Mammals

6. Adaptation for Wind Pollination (Anemophily):
• Flowers are small, colorless, inconspicuous,
nectar less and become arranged as inflorescence.
• Inflorescence are compact.
• The anthers are well exposed for the easy
dispersal of pollen grains.
• Pollen grains are small, light, dry, dusty, non-
sticky and sometimes even winged.
• The stigmas are large, hairy and feathery or
branched to catch the air borne pollen grains.
• Flower often have single ovule in a Ovary.
• E.g., Grasses, Sugarcane (Saccharum), Bamboo
(Bambusa) and Coconut (Cocos nucifera), etc

7. Adaptations for Water Pollination (Hydrophily):
• It is quite rare in flowering plants and is
limited to about 30 genera, mostly
monocotyledons.
• Flowers are small, colorless, inconspicuous,
odorless and nectar-less and pollen grains and
stigmas are generally unwettable.
• The stigmas are long and sticky, e.g.,
Vallisneria, Hydrilla and Zostera.
• In Vallisneria, the female flower reach the
surface of water by the long stalk and pollen
grains are released on to the surface of water.
They are then carried by the passive water
currents.
• In most of the water pollinated species, pollen
grains are protected by mucilaginous covering.
Note: Not all aquatic plants use water for
pollination. In a majority of aquatic plants, the
flowers emerge above the level of water and are
pollinated by insects or winds as in land plants,
e.g., water hyacinth (Eichornia) and lily.

8. Adaptations for Insect Pollination (Entomophily):
• Most of the flowers are Entomophily in
pollination.
• Insect-pollinated flowers are large, colorful,
fragrant and rich in nectar.
• A number of flowers are clustered into an
inflorescence to make them conspicuous.
• Flowers have nectar glands and are highly
fragrant to attract insects.
• The surface of pollen grains is sticky due to
exine layer and stigma is sticky due to
mucilaginous layer.
• Nectar and pollen grains are floral rewards for
the insect pollinators..
Note: 1. The flowers pollinated by flies and beetles
secrete foul odors to attract these animals.
2. Night blossoming flowers which are entomophily
are white colored, and have strong smell.
Pollination by Honey bee

9. Adaptations for Insect Pollination (Entomophily):
• Floral rewards for flowers can be:
o In some species, floral rewards are to
provide safe place to lay eggs, e.g., for
the tallest flower of Amorphophallus
(about 6 feet in height).
o In plant Yucca, moth and the plant,
cannot complete their life cycles without
each other. The moth deposits its eggs in
the locule of the ovary and the flower, in
turn plant gets pollinated by the moth.
The larvae of the moth come out of the
eggs as the seeds start developing
Pollination in Yucca by Moth

10. Requirements for Autogamy
• A synchronization between pollen release and
stigma receptivity and also, the anthers and
the stigma should .
• Flower should either be,
› Cleistogamous- Flowers which do not open at
all In such flowers, the anthers and stigma lie
close to each other. When anthers dehisce in
the flower buds, pollen grains come in contact
with the stigma to effect pollination.
OR
› Chasmogamous flowers which are similar to
flowers of other species with exposed anthers
and stigma

11. Outbreeding Devices:
• Flowering plants have developed many devices to discourage self-
pollination and to encourage cross-pollination.
• Because the majority of flowering plants produce hermaphrodite flowers
and are likely to come in contact with the stigma of the same flower.
• The continued self-pollination leads to chances of inbreeding
depression.

12. Devices to prevent inbreeding are:
• Dichogamy: Receptivity of pollen release and stigma is not
synchronized.
› Protandry: When the pollens released before the stigma becomes
receptive.
› Protogyny: When stigma becomes receptive before the release of pollen.
• The anther and stigma are placed at different positions, so that the pollen
cannot come in contract with the stigma of same flower which will
prevent autogamy.
• Self incompatibility: Inhibition of pollen tube growth on the stigma of
the same flower.

13. Devices to Prevent inbreeding are:
• Production of unisexual flowers, i.e., autogamy is prevented, if both male and
female flowers are not present on same plant, e.g., castor and maize
(monoecious).
• Both autogamy and geitonogamy is prevented in several species like in Carica
papaya, if male and female flowers are present on different plants, i.e., each plant
is either male or female (dioecy).
• Heterostyly: Sometimes due to great disparity in the length of style and stigma,
effective self pollination is not possible, e.g., Primula, Lathynis, Oxalis etc.
• Herkogamy : Unusual Mechanical or Chemical Barriers for promoting
outbreeding. Examples-
• In flowers of Caryophyllaceae, the stigma grows much beyond the limits of
stamens so that its own pollen-grains fail to reach its own stigma.
• In Calotropis, the corolla act as hood in between and androecium and gynoecium.

14. Pollen Pistil Interaction
• A large number of Pollens releases from the
flower So, Pollens of any species can land over
the stigma of any flower.
• So., after the pollination it is required that a
recognition between stigma and pollen landed
over the stigma.
• There is a chemical reaction take place between
the Stigma and Pollen grain for the recognition
purposes.
• These set of reactions collectively termed as
Pollen-pistil interaction.
• The successful interaction leads to germination
of Pollen grain and entry of Pollen tube into
Ovule through Style.

15. Germination of Pollen Tube-
• In flowering plants, however, the ovules are contained
within a hollow organ called the pistil, and the pollen
is deposited on the pistil’s receptive surface, the
stigma.
• On the stigma, the germination of pollen grains begins
by absorption of water and nutrients and the pollen
grain produces a tiny pollen tube through the style to
the ovary.
• The tube cell enlarges and comes out of the pollen
grain through one of the germ pores to form a pollen
tube. The tube nucleus descends to the tip of the pollen
tube.
• And enters into ovule and then into embryo sac, by
which two male gametes also enters into ovule and
then into embryo sac.

16. Ways of Entry of Pollen Tube in the Ovules
• There can be following ways of entry of
Pollen tube into the ovules-
› Porogamy- When Pollen tube enter to the
Ovule through the Micropyle of the Ovules.
› Mesogamy- When Pollen tube enter to the
Ovule through the Integuments of the Ovules.
› Challazogamy- When Pollen tube enter to the
Ovule through the Micropyle of the Ovules. Obturator is a special structure that facilitates
the entry of the pollen tube into the ovule of a
flower.
Filiform apparatus Guides the Entry of
Pollen tube into the Ovule.

17. Fertilization:
• The process of Double Fertilization is the important
feature of Angiosperms.
• When pollen tube enters the embryo-sac (inside the
ovule), it bursts to release its contents i.e., two sperms
along with certain amount of protoplasm .The first
male gamete discharge in one of the synergid.
There are following two steps of Double Fertilization-
1. Triple Fusion- The remaining sperm now fuses with
the two haploid polar nuclei (present in the center of
embryo sac). This fusion is called as triple fusion (as
three nuclei i.e., one male gamete and 2 polar nuclei,
are fused). This results in formation of Primary
Endosperm Nucleus (PEN).
2. Syngamy- One of the two sperms goes to fertilize the
egg cell. This fusion is called syngamy. It results in
the formation of zygote, which gives rise to proper
embryo.
Male Gamete (N)+Egg (N)= Zygote (2N)
Male Gamete(N)+Polar Nuclei (2N)= PEN (3N)

18. Thank You!!!!