UPSC Civil Services Model Paper 7

Autogamy
In this type, pollination is achieved within the same flower .
Transfer of pollen grains from the anther to the stigma of the same flower.
In a normal flower that opens and exposes the anthers and the stigma, complete autogamy is rather rare .
Autogamy in such flowers requires synchrony in pollen release and stigma receptivity and also, the anthers and the stigma should lie close to each other so that self-pollination can occur.
Some plants such as Viola (common pansy), Oxalis , and Commelina produce two types of flowers : chasmogamous flowers which are similar to flowers of other species with exposed anthers and stigma, and 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 .
Thus, cleistogamous flowers are invariably autogamous as there is no chance of cross-pollen landing on the stigma.
Cleistogamous flowers produce assured seed-set even in the absence of pollinators.
Geitonogamy Transfer of pollen grains from the anther to the stigma of another flower of the same plant.
Although geitonogamy is functionally cross-pollination involving a pollinating agent, genetically it is similar to autogamy since the pollen grains come from the same plant.
Xenogamy Transfer of pollen grains from the anther to the stigma of a different plant.
This is the only type of pollination which during pollination brings genetically different types of pollen grains to the stigma.