maj
2008
Flowering and Fruiting in Plants
Some knowledge of the flower structure and fruit setting is necessary to understand the entire pollination process. All flowers have the same basic pattern, but there are many variations. The peach blossom, the tassel and ear of corn, and the sunflower head appear remarkably different, but all have the same basic parts.
Typically, the flower is composed of the sexual organs, protected by the usually colorful delicate petals that may form a sort of tube or crownlike corolla. These are supported and partially protected by the usually green and more durable sepals, collectively called the calyx. The calyx and corolla combined are referred to as the perianth. There may be leaflike bracts just below the sepals.
The male parts of the sexual organs are the stamens and there may be one to several dozen in a flower. The stamens usually consist of hairlike filaments bearing the pollen-producing anthers on the outer ends. At the appropriate time, the anthers dehisce or split open and disgorge the male element, the numerous microscopic and usually yellow grains of pollen.
The female part of the flower is the pistil, consisting of the ovary, with one to numerous ovules or potential seeds, and extending from the ovary is the style, with the pollen-receptive portion, the stigma, on or near the tip. The pistil may be composed of one or more carpels or sections. Typically, the ovary, with its style and stigma, surrounded by the stamens, occupies the central area of the flower. Nectar usually is secreted at the base of the pistil, inside the corolla. Nectaries also may occur outside the corolla. These usually are referred to as extrafloral nectaries and do not contribute to pollination.
The ovules produce the seeds, and the ovary develops into the fruit. Usually one ovule must be fertilized for each seed that develops. if no seeds are produced, the fruit is unlikely to develop although a few fruits (certain cucumbers and citrus varieties) develop parthenocarpically (without being pollinated). if an insufficient number of seeds develop, the fruit is likely to be asymmetrical or otherwise not fully developed.
In general, the sooner pollination can occur after a flower opens, the greater the likelihood that fertilization of the ovules and seed development will occur. As time elapses, the pollen may be lost to insect foragers, wind, gravity, damage by heat, moisture, or drying out. Also, processes may set in that result in the shedding of the fruit.