2. The process of transfer of pollengrains from the anther to the stigma of
flower is called pollination
Essential for fertilization and development of embryo
Depending on the source of pollen, pollination is of 3 types
Autogamy
Geitonogamy
Xenogamy
3. AUTOGAMY
Transfer of pollen grains from the anther to the stigma of the same flower
Conditions for autogamy:
Flower must be bisexual
Synchrony in the pollen release and stigma receptivity.The anther and pistil mature simultaneously
Anther and stigma lie close to each other
Some plants such as Viola (common pansy), Oxalis, and Commelina produce two types of flowers –
chasmogamous flowers , flowers with exposed anthers and stigma, and cleistogamous flowers which
do not open at all
Autogamy is the only method of pollination in cleistogamous flowers.
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.
Cleistogamous flowers produce assured seed-set even in the absence of pollinators
cleistogamy is advantageous or disadvantageous to the plant? Why?
Ans: inbreeding depression
4.
5. GEITONOGAMY
Transfer of pollen grains from the anther to the stigma of another flower of
the same plant.
geitonogamy is functionally cross-pollination involving a pollinating agent
But genetically it is similar to autogamy since the pollen grains come from the
same plant
XENOGAMY/ CROSS POLLINATION/ ALLOGAMY
6. Outbreeding devices / Conditions for Xenogamy
Majority of flowering plants produce hermaphrodite flowers and pollen grains are likely to come in
contact with the stigma of the same flower.
Continued self-pollination result in inbreeding depression
Devices to prevent self pollination and to increase cross pollination are:
In some species, pollen release and stigma receptivity not synchronized
Either the pollen is released before the stigma becomes receptive or stigma becomes receptive
much before the release of pollen
the anther and stigma are placed at different positions so that the pollen cannot come in contact
with the stigma of the same flower
Plant monoecious- unisexual flowers- prevent autogamy Eg; Maize,Caster
Plant dioecious- male & female flowers different plant- prevent both autogamy and geitonogamy
Eg; Datepalm, papaya
self-incompatibility- Genetic mechanism that prevents the germination of pollengrains on the stigma
of same flower/ another flower of the same plant.
7. POLLINATING AGENTS
External agents which help in pollination
2 types- Abiotic agents- Wind, Water
Biotic agents- Insects, birds, reptiles, mammals
ABIOTIC AGENTS: The contact of pollengrains with stigma is a chance factor
both in wind & in water pollination. So only small no: of plants use abiotic
agents for pollination.
8. WIND POLLINATION ( Anemophily)
Common method
Special features
Produce large no: of pollengrains
Pollen grain are light, dry & non sticky-transported in wind currents
Sometimes they have wing like structures : eg; Pinus
Stigma is large, feathery –trap air borne pollengrains
Flowers normally have a single ovule in the ovary
Flowers are arranged as infloresense : eg; corn cob
Eg: Grasses, maize, cannabis
9. WATER POLLINATED ( Hydrophily)
rare in flowering plant , limited to about 30 genera, mostly monocotyledons.
In lower plant groups such as bryophytes & pteridophytes water is the
medium of transport of male gamates.
for some bryophytes and pteridophytes, their distribution is limited because
of the need for water for the transport of male gametes and fertilisation.
Special features
Pollengrains are light & protected from decaying- mucilaginous covering
Stigma is sticky and unwetable due to waxy coating
Eg: Vallisneria, zostera, hydrilla
10. In vallisneria, the female flower reach the surface of water by the long stalk and the
male flowers or pollen grains are released on to the surface of water, reach female
flower through water current. After pollination female flower sinks down.
In Zostera ( Sea grasses), female flowers remain submerged in water and the pollen
grains are released inside the water.They are long and ribbon like. They coil around
female flowers and pollination takes place.
All aquatic plants do not use hydrophily.
Majority of aquatic plants flowers emerge above the level of water and are pollinated by
insects or by wind
Eg: Water hyacint
12. INSECT POLLINATION ( Entomophily)
Flowers are large,if small they are grouped in inflorescence
Flowers are brightly coloured, scented/ with foul odour ( flies, beetle
pollinated)
Produce nectar
Pollengrains & stigma are sticky
Nectar and pollen grains are the usual floral rewards
Eg; Jasmine, Sunflower.
13. BIRDS POLLINATION ( Ornithophily)
Flowers are large & funnel shaped
Brightly coloured
Produce large amount of nectar
Pollen grains are sticky
Animal pollinated flowers give certain rewards to the pollinators.Explain it?
Ans: The flowers provide nectar & pollengrains as food
Some species provide safe place for laying egg, Eg; Amorphophalis & Yucca
A species of moth and the plant Yucca– cannot complete their life cycles without each other.
The moth deposits its eggs in the locule of the ovary and the flower, in turn, gets pollinated
by the moth. The larvae of the moth come out of the eggs as the seeds start developing.
YUCCA &
Moth
14. Importance of pollination
Pollination leads to fertilization, production of seeds and fruits
Cross pollination- genetic recombination- new species
Cross pollination- disease resistant, high yielding plant varieties
Productivity can be increased by the availability of suitable pollinating agents
Seeds and fruit formed after fertilization- source of nutrients for animals
including man
Essential for the perpetuation of species
