Tom Loo, age 13, of Columbus, Ohio, for his question:
HOW DOES POLLINATION WORK?
Pollination is the transfer of pollen from the stamen, or male structure, of a flower, to the stigma of the pistil, or female structure, of the same or a different flower.
In self pollination, or autogamy, the pollen is transferred from the stamen to the stigma of the same flower. In cross pollination, or allogamy, pollen is transferred from one flower to another on the same plant (geitonogamy) or to a flower of another plant of the same species (xenogamy).
Self pollination is the simpler and more certain of the two fertilization processes, especially for many species that colonize by copiously repeating the same parental strain. A species producing such uniform offspring, however, runs the risk of having its entire population wiped out by a single evolutionary event. Cross pollination produces more varied offspring that are better able to cope with a changed environment.
Cross pollination of plants also tends to produce more and better quality seeds.
The advantages of cross pollination are such that plants have evolved elaborate mechanisms to prevent self pollination and to have their pollen carried to distant plants.
Many plants ensure against self pollination by producing chemicals that prevent pollen from growing on the stigma of the same flower, or from developing pollen tubes in the style. Other plants, such as date palms and orchard trees, have become dioecious, producing only male flowers on some plants and female flowers on others.
Wind is the most common pollen carrier for cross pollination. Because wind scatters pollen indiscriminately over wide areas, such trees as conifers must produce huge quantities of pollen to ensure fertilization, often enveloping pine forests in a haze of pollen.
The date palm, which is dioecious, is wind pollinated in nature but has been artificially hand pollinated in the Middle East for many centuries.
Bees, other insects, birds and bats are more discriminate pollen carriers than the wind because they are attracted to flowers of the same species.
The relationship between some plants and bees is so specific that only certain bumblebees, entering such flowers at Scotch broom, cause the stamens to spring up and dust the underside of the bees with pollen.
Perhaps the most important cross pollinators of flowers are honeybees, whose hives are often placed in orchards for this purpose.
Species of big tongued tropical bats are drawn to specialized flowers that attract the animals by nocturnal odors and large quantities of nectar and protein rich pollen.
There are about 250,000 species of mosses, liverworts, ferns, plants, bushes, vines, trees and other forms that mantle the earth and are also found in its waters. That's a lot of plants and most of them require some form of pollination to reproduce.