| Calyx or sepals, | + | Corolla or petals, | + | Stamens consisting of filaments and anthers, | + | Pistil consisting of ovary, style, and stigma. |
The stamen is the male organ of reproduction and the pistil the female. The actual process of fertilization, pregnancy, the forming of the fruit and later the seed, and the latter’s birth of a new plant, comprise one of the most fascinating of those provisions of nature which secure the perpetuation of the plant world. In the life history of even the commonest weed along the roadside there is this constant renewal of life by sexual reproduction, just as in animals and in man. In the chapter on “How Plants Produce Their Young” will be found some account of this supreme function of flowers, after which, as if their usefulness were over, they wither and perish.
Not all flowers are perfect or complete. Some lack petals, as the buckwheat, where the colored calyx replaces petals. Others have neither calyx nor corolla, as in the sycamore or plane tree. Most plants, however, have both calyx and corolla. In some very few plants certain of the flowers have no stamens, when they are said to be pistillate or female flowers, and certain others have no pistils, when they are called staminate or male flowers. In other words, the sexes are in different flowers in the same cluster or plant, as is true of the walnut and hickories, when they are said to be monœcious. In still others the sexes are on entirely different plants, in which case they are diœcious, as in practically all willows. In the latter case there are pistillate or female plants and staminate or male plants.
While it is a commonplace that peas do not look like daisies, nor a carnation like a rose, this simple observation does not begin to tell us of the wonderfully different flower shapes and colors that are to be found along any roadside. The perfect and complete flower that we have been studying is quite regular, composed as often as not of four or five petals, as many sepals, with five or ten stamens and perhaps a single pistil. Yet there is literally no limit to the variations from this scheme, and some of these must be understood here in order that the life-histories and behavior of plants discussed in later chapters may tell their full story.
The figures on page 44 show a regular flower, with five separate petals and sepals ([Fig. 39]). Such flowers are said to be polypetalous, i.e., separate petals. Sometimes three of the petals are larger, two smaller, in which case the flower is lopsided or, as it is said, inequilateral. Again all the petals are united to form a regular and equilateral tube, as in lily of the valley, when they are gamopetalous, i.e., united petals ([Figure 42]). As we shall see in the chapter on Plant Families, this is a distinction between two great groups of plants, as important in their classification as negro and white man are in classifying humans.
In peas, beans, the locust tree, and related plants the petals are much changed to form an irregular flower, with a keellike or prow-shaped part made from the uniting of two petals. Two more unite to form the wings, and the remaining and larger petal forms the standard. Figure 40 and the explanation under it illustrate this unusual form of flowers.
Our common garden salvia shows still another type of flower, which is tubular and irregular ([Figure 41]). There is an arching, hoodlike structure at the top overhanging a lower lip. This kind of irregularity is common in thousands of different sorts of plants and, usually, it is a device to insure fertilization of the flower by insect visitors. So necessary are these for pregnancy in many plants, that an orchid, once discovered in Madagascar with a tube eighteen inches deep, puzzled the botanists, who were unable to understand how the plant produced seed in the absence of any known insect with a tongue as long as that. Darwin said at once that such an insect would one day be discovered on that island. Years after, Baron von Humboldt, a German naturalist, found the insect and explained the mystery.
Perhaps there is no feature of plant life that shows such an amazing amount of variation as the forms of flowers, and while only a few of the simplest deviations from the normal have been discussed here, it must not be forgotten that this infinite variety is a reflection of the ingeniousness of nature in securing a plentiful supply of seed. Form, color, the secretion of sweetish nectar, the night or day blooming of different kinds of flowers, every device that will make fertilization certain, by the flower itself, by insects, or even by the wind, is used in such prodigal fashion, that we come to see the importance of it to all plants only by a realization of the complexity of it and the provisions against its failure.
One apparently most lavish method of securing fertilization is the arrangement of flowers in clusters. While many flowers are quite solitary, the great mass of individual plants produce a few or dozens, or even hundreds of flowers—in fact, certain relatives of the common carrot may produce over a thousand flowers in a single cluster. The form and plan of arrangement of these clusters follows a rather definite scheme, and here, as in the case of leaves and parts of individual flowers, the figures tell the story better than words. In the common dandelion and daisy, and their thousands of relatives, the “flower” ([Figures 43-45]), as commonly understood, is really composed of scores or even hundreds of true flowers in each head. In the case of the daisy the yellow center, if picked apart, is seen to be really made up of scores of tiny tubular flowers, each just as truly a flower as a single rose. The rays, or what are incorrectly called “petals,” which fringe the golden center with white, if carefully separated and examined closely, will be found to be also a complete flower, the true petals of which are all joined to make the strap-shaped ray. If one looks sharply, the united edges of these petals may be seen by the ridges or channels that represent their joined edges. Because plants of this sort produce two sets of flowers in each head, one conspicuous by its brightly colored rays and with another tubular set in the center which makes doubly certain the fertilization and seed supply, they are considered the most highly developed of all plants. It is not a close aristocracy, nor an exclusive one, for over eleven thousand different kinds of plants, scattered all over the world, have their flowers arranged in this fashion or some slight modification of it. They possess, above all others, the certainty that there will be no slip in their fertilization, pregnancy, and subsequent birth of a new generation. Because this is the great object of all flowers, and these daisylike plants have brought it to such perfection, they are most surely to be classed as the highest type upon the earth to-day.