The Pollination of Flowers.
Value of the Honeybee in Cross-fertilization.
If some common flower such as a rose or a buttercup is selected for examination, it will be seen to consist of numerous small thread-like organs surrounded by two whorls of leaves. The outer circle of leaves is green, and forms the calyx, each leaf of which is called a sepal. The office of the calyx is to protect the inner and more delicate organs, especially in the bud, when the calyx alone is visible. The second circle of leaves is large and bright-colored—red, white, or yellow in the rose, and yellow in the buttercup; this is the corolla, and each leaf is known as a petal. The brilliant hues of the corolla are the stamens, composed of slender stems, and the filaments, bearing the four-celled anthers, which contain fine grains of powder known as pollen. In the center of the flower stand the pistils. Usually a pistil consists of three parts—the ovary, style, and stigma; but the style is sometimes wanting. The base of the pistil is the ovary, and is a capsule containing the nascent, unfertilized ovules; the style is a porous stalk rising from the ovary, and bearing at its upper end a glutinous receptive surface called the stigma. Pollination is the transference of pollen from the anthers to the stigma. If the pollen is from the same flower it is self-pollination; but if it is from a different flower of the same species it is cross-pollination. Cross-pollination between the flowers of different species is hybridization.
Soon after a grain of pollen has lodged on the stigma, if the proper conditions exist, it sends out a slender tube which grows down through the porous style, by which it is nourished, until it comes to one of the ovules in the ovary. It enters the ovule by a little orifice (micropyle,