Pollination is the transfer of pollen from the anther to a receptive stigma of a flower. In nature, wind, insects, birds or mammals accomplish the task. Plant breeders or home gardeners can hand pollinate or artificially pollinate plants. Although pollination is one of the steps necessary for fruit and seed development, fertilization is also necessary. The two terms are often confused and should be distinguished from each other because fertilization does not always follow pollination.
Plants display many wonderful adaptations and mechanisms developed for the purpose of aiding pollination. Some species are entirely dependent upon bees and other insects for the transfer of pollen. Their flowers often possess special features that attract insects like color, odor, and nectar. Some plants are dependent upon mammals like bats or hummingbirds. Still others depend on the wind for pollen transfer. Imagine pollen floating for hundreds of miles on the wind currents of the upper atmosphere before reaching a receptive stigma. Some plants produce more vigorous seed when they have been cross pollinated (receive pollen from another plant of the same species) while the flower structure of others are such that only the pollen from their own stamens can reach their stigma. These flowers are called self-pollinated.
As mentioned earlier, successful pollination does not mean successful fertilization. Once the pollen grain is in place on the stigma, it begins to develop a tube-like projection, which pushes through the surface of the stigma, extends in length, growing downward through the entire length of the style, until it reaches the ovary at the base. There it seeks out an ovule, fertilizes it, and the combination then develops into a seed. Many pollen grains may settle on the stigma of a single flower, send their elongating tubes into the ovary, and thus bring about the development of a fruit containing seeds. Every plump pea in a pod has been fertilized in this manner; the small flat ones are the ovules that no pollen has reached. Every kernel of corn has been fertilized by a pollen tube that has grown all the way down the silk--each strand of which is the style of a pistillate flower.
Certain environmental conditions can inhibit pol fertilization. Extremely wet or cold weather when pollen is being dispersed will cause poor fruit set. Extended periods of freezing temperatures can destroy flower buds. Sudden late frosts will cause irreparable damage to flowers and young fruit. On the other side, excessively hot and dry summer weather can cause blossom drop and result in poor fruit set for many vegetable crops. Regular, thorough irrigation is critical to promote flowering and fruiting especially with vegetable crops. Many gardeners question how various vegetables are pollinated. This is important to know when collecting and saving seed for use next year. It also helps explain some of the challenges involved when fruit set does not live up to our expectations. Listed below are several common vegetables and their method of pollination.
|Broccoli (Insect)||Cabbage(Insect)||Carrot (Insect)|
|Eggplant (Self)||Muskmelon (Insect)||Pea (Self)|
|Tomato (Self)||Watermelon (Insect)|
As the gardening season is getting under way, consider the wonders of seed production. Pollination and fertilization allow the species to survive and give gardeners a chance to harvest a bountiful crop.
This article originally appeared in the March 22, 1996 issue, pp. , 1996 issue, pp. 33-34.