Plant pollination is almost as diverse as the plant community itself. Self-pollination occurs in some plant species when the pollen (male part) produced by the anthers in a single flower comes in contact with the stigma (female part) of the same flower or with the stigma of another flower on the same individual. Self-pollination does not allow much modification in the genetic makeup of the plant since the seeds produced by self-pollination create plants essentially identical to the individual producing the seed. A plant population that has all individuals identical in form, size, and growth requirements has little possibility of modifications to allow for change in its environment.

Most plant species have evolved ways to ensure an appropriate degree of interchange of genetic material between individuals in the population, and cross-pollination is the normal type of pollination. In this case flowers are only pollinated effectively if...