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GARDENING : Knowing the Facts of Plant Life Can Produce Results

July 06, 1991|EARL ARONSON | ASSOCIATED PRESS

Many gardeners take plant reproduction for granted. Garden and landscape plants produce seeds as a result of pollination, a process often as complex as the terminology associated with it.

Putting it into focus is Ray Rothenberger, a University of Missouri horticulturist.

Many food plants, such as garden vegetables and orchard fruits, have flowers that contain both the male parts (stamens) and female parts (pistils). Such flowers are normally called complete flowers or hermaphroditic.

These may be pollinated by wind or insects, but some produce pollen that cannot pollinate the same flower, or the structure is such that the wind or an insect visiting the flower cannot self-pollinate it. Such flowers must be cross-pollinated with pollen from flowers of another plant of a different variety.

Prime examples of such fruits are apples and many plums. When looking at the flowers, Rothenberger says, there is no way to tell whether pollination can take place.

"Not all plants produce complete flowers," he explained. "Flowers may contain only male parts (staminate flowers) or only female parts (pistillate flowers). If a plant produces only male flowers on one plant and only female flowers on another plant, we call the plant species dioecious, and we say that we have male and female plants.

"Some of the best-known plants we use in landscape with this characteristic are such shrubs as holly, bayberry and juniper, or trees such as ash and ginkgo."

Many other plants, whose flowers have only male parts or female parts, are called monoecious, meaning that they have male and female flowers in "house." Cucumber and watermelon, and trees such as birch, alder, pine and oak fit this category.

This knowledge can help you select plants.

Where seeds can be messy or smelly, such as in ash and ginkgo trees, select only male plants and no fruits will be produced.

In plants bearing both male and female flowers, the male and female flowers may not be able to pollinate each other. In the vine crops, male flowers are produced before the female flowers, so the first flowers will not set fruit; however, with time, the female flowers will develop.

"To cause earlier production, plants able to produce only female flowers have been developed," Rothenberger said. "These are called gynecious since they are not really dioecious. Normal plants with pollen-producing male flowers must be available to allow gynecious plant flowers to be pollinated and develop, unless they happen to be parthenocarpic. This means fruits are able to develop without pollination.

"The complex and unusual flowers and pollination requirements of plants have allowed them to exist and develop over millions of years.

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