confused, but it is clear that they are very different functions. Fertilization does not always occur immediately after pollination; the flowers of the witch hazel are pollinated in autumn, but fertilization does not occur until the following spring; and in the case of pine trees fertilization may not take place until two years after pollination.
But there are comparatively few flowers which, like the buttercup and rose, have all the members present, separate, and regular in form. Many flowers have a part of the organs wanting. The wind-pollinated cat-tails, pondweeds, grasses, and sedges have neither calyx nor corolla, or they are represented only by scales and bristles. Wind-pollinated flowers are small, green or dull-colored, nectarless, and usually scentless. Many hard-wood trees have the stamens and pistils in separate flowers. In Jack — in — the — pulpit the flower is reduced to a single pistil or stamen.
Flowers may be modified also in another way by the fusion or consolidation of the organs. Tubular calyces and corollas, as in the morning-glory and phlox, are stronger and better adapted to protect the nectar than those which consist of separate sepals and petals. In the pulse family the stamens are commonly fused into "brotherhoods." But fusion is nowhere so common as among the pistils. So long as they are separate, pollen must be placed on the stigma of each; but when they are consolidated, one application may serve to fertilize all the ovules. Clearly a flower like the buttercup, where all the parts are separate units, is more primitive than an orchid, where they have coalesced to such an extent that it is difficult to determine their number. In primitive families, again, like the buttercups, mallows, roses, and saxifrages, the flowers, as a rule, have regular forms, the petals are all alike, and are usually white or yellow; but in many families, which have developed more recently, the flowers have assumed strange, bizarre forms, as in the sweet pea, snap-dragon, and sage, and frequently are red, purple, or blue in color. The purpose of these singlar forms is to compel an insect to pursue a fixed path in its visits and thus effect pollination. Such, flowers are the youngest and latest to appear in the plant world. The larkspur is of later origin than the buttercup, and the clover blossom than the rose.
What is the role or function of these varied forms, mechanisms, colors, and odors? Their purpose is to secure pollination. This is the significance of the flower. Self-fertilization is better than sterility, but crossing is an advantage. Crossed plants grow more vigorously, bloom earlier and more profusely, and produce more seed capsules. Inbred races tend to disappear. While hybrids between different species often show decreased fertility, there are thousands of cases in which they multiply readily by seed. They show greater variation than the parent forms, have more and larger leaves, stronger stems, better root-systems, bloom sooner, and the forms are larger, better scented, more intense in color, and more persistent. Among the higher plants (Angiosperms) pollination is effected chiefly by the agency of the wind, insects, and birds.
All attempts to explain the structure of the flower failed until the discovery of sex in plants, and, incredible as it may seem, this has been universally recognized for less than one hundred years. In 1694 Camerarius of Tubingen put the question to plants themselves by experiment, and learned that seed, “the most perfect gift of nature,” was not produced unless pollen was placed on the stigma. Later James Logan, Governor of Pennsylvania, helped to prove the truth of this theory by experiments with Indian corn.
The lowest and simplest plants consist of one cell, and are usually very small jn size. They have no reproductive organs, and multiply by dividing into two