The process of transfer and deposition of pollen grains from the another to the stigmatic surface of the flower is called pollination. It is an essential event in the sexual reproduction of seed bearing plants. Pollination is a pre-requisite for ensuring seed set and perpetuation of a species. Pollination is direct in Gymnosperms and indirect in Angiosperms.
There are two main types of pollination - self pollination and cross pollination.
It is the process of transfer of pollen grains from the another to the stigma of either the same flower or another flower borne on the same plant. Accordingly, self pollination is of two types: autogamy and geitonogamy.
It is a kind of pollination in which the pollen from the anthers of a flower are transferred to the stigma of the same flower. It occurs by three methods.
Some plants never open to ensure complete self-pollination. This condition is called cleistogamy, eg. Commelina bengalensis,Oxalis, Viola, etc. The cleistogamous flowers are bisexual small, inconspicuous, colourless and do not secrete nectar.
Anthers and stigma of the bisexual flowers of some plants mature at the same time. They are brought close to each other by growth, bending or folding to ensure self pollination. This condition is called homogamy, eg., Mirabilis (Four O. clock), Catharanthus (Vinca), Potato, Sunflower, etc.
Anthers and stigma of the bisexual flowers of some plants mature before the opening of the buds to ensure self-pollination, eg.,Wheat, Rice, Pea, etc.
It is a kind of pollination in which the pollen grains from the anthers of one flower are transferred to the stigma of another flower borne on the same plant. It usually occurs in plants which show monoecious condition (unisexual, male and female flowers are borne on the same plant).
1. Chances of pollination are more.
2. Self-pollination maintains purity of the race and avoids mixing.
3. It need not produce a large number of pollen grains.
4. Flower need not possess devices such as large and showy petals, presence of scent and nectar, etc. to attract pollinators.
1. Progeny continuously gets weaker after every generation.
2. Less chances of the production of new species and varieties.