Pollination is the transfer of pollen from the male part of the plant, anther, to the female part, stigma. Pollination is necessary for fertilization and reproduction, in other words, for the propagation of plants. It can be either cross-pollination or self-pollination.
In cross-pollination, the transfer of pollen takes place from the flower of one plant to that of another plant of the same species, usually by external means such as wind and insects. In the case of self-pollination, the pollen transfer occurs within the same flower. It is usually observed in legumes (such as peanuts), orchids, wheat, rice, oats, etc. A relatively small amount of pollen is transferred from anther to stigma, as compared to cross-pollination. Self-pollination leads to more uniform progeny and the plant does not have to spend energy on attracting pollinators. It results in perfect flowers as compared to cross-pollination, which causes both perfect and imperfect flowers.
Pollination usually involves pollen from flowers of other plants of the same species fertilizing the ovules which leads to the formation of the seed ultimately. In self-pollination the flower has a structure that allows the stamens and the stigma to contact each other and thereby the flower is pollinated.
Self-pollination is found to occur in some species like sunflower, soybeans, peas, peanuts, etc. These plants use self-pollination only as a last resort, if cross pollination has not occurred. This is due to the fact that self-pollination leads to the plants that grow from the seeds produced having genes similar to the parent plant. And it is essential that the progeny not be like the parent for the development of the species. Self-pollination is helpful in a few cases where there are only a few plants in the geographical area or if the number of pollinators is very small.
Self pollination is the transfer of pollen grains from the anther to the stigma of a flower ,on the same flower ,of the same species