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Transfer of pollen grains from anthers to the stigma.

(A) Self-pollination (Autogamy):

Transfer of pollen grains within the same flower e.g., pea, wheat and rice.

(B) Cross-pollinaion (Allogamy):

Transfer of pollen grains from one flower to another.

(1) Xenogamy:

Transfer of pollen grains from one plant to another of the same species.

(2) Gietnogamy:

Transfer of pollen grains from one flower to another on the same plant. Also called genetically self pollination.

(3) Hybridism:

Transfer of pollen grains from one plant to another related allied species.

Advantages of cross pollination:

Heal their progeny of offsprings, better adaptability, production of new varieties, more number of viable seeds etc.

Advantages for self-pollination:

(A) Homogamy:

Anthers and stigmas of a flower mature at the same time e.g., in Brassica and Gardenia florida.

(B) Cleistogamy:

Flowers remain closed. They never open throughout their life span e.g., in Arachis hypogea (ground nut) and Commelina bengalensis.

(C) Geitonogamy:

Transfer of pollen grain from one flower to another on the same plant e.g., Triticum aestivum.

Advantages of cross-pollination:

(A) Dicliny (unisexuality) : e.g., pumpkin, palm, cucumber.

(B) Self sterility: e.g., Tea, Malva, Orchids.

(C) Dichogamy: Anther and stigma of a flower mature at different times.

(i) Protandry: Anthers mature earlier than the stigmas of the same flower e.g., Cotton.

(ii) Protogyny : Stigma matures earlier than the anthers of the same flower e.g., Ficus.

(D) Heterostyly: Stamens, style and stigma are of different heights.

(E) Herkogamy: A natural barrier develops between anthers and stigma to check self pollination e.g., Calotropis.

Anemophily:

Pollination by wind; Flowers are colourless; pollen grains are produced inlarge amount; style and stigma are hairy e.g., Bambusa, Saccharum, grasses, wheat, maize, rice, barley and palms.

Entomophily:

Pollination by insects; rough and sticky pollen grains; insects are attracted by necter/scent/colour. Example of insects is bees, butterflies and moths. The flowers of Asteraceae and Labiatae families are generally pollinated by the bees and butterflies.

Hydrophily:

Pollination by water currents; pollen grains are sticky e.g., Vallisneria, Hydrilla, Ceratophyllum, Zostera etc.

Zoophily:

Pollination by animals e.g., in Bombax (silk cotton) by birds (Ornithophily), in Anthocephalous, Adamsonia and Kigelia by bats (Cheiropterophily); in Arisaema by snakes (Ophiophily), in Colocasia by snails (Malacophily).