ORGANS OF INCREASE AND REPRODUCTION—THE FLOWER—THE CALYX—THE COROLLA—THE STAMEN—THE PISTIL.

Some of the simplest plants are propagated by spores, which are detached, and fall upon the ground to vegetate; but in the case of the higher orders the reproduction of species is a much more elaborate process, and is carried on by means of certain organs called flowers. Small buds, or ovules, are formed, which develop into seed. Plants also produce buds, which grow upon various parts of it, and are capable of reproducing their species. We will first speak of Flowers.

Flowers are not only the lovely blossoms we cut and place in our rooms, but the reproductive organs of plants which may be very plain and simple or gorgeous and fragrant, and in all probability the so-called flowers are few in comparison to the unrecognized flowers. Trees and bushes flower equally with the rose and the pink and carnation. Vegetables flower as well as the lily, though we do not recognize it so well. Let us now examine the “flower.”

Flowers may consist of four parts, but it is not absolutely necessary that they should contain more than two. The four portions of a complete flower are—

1. The Calyx.
2. The Corolla.
3. The Stamen.
4. The Pistil.

The two last mentioned are essential. The four organs are placed around a pedicel or peduncle (flower stalk), and are known as floral whorls.

The Calyx is the outermost whorl of all when all exist. The portions of the calyx are known as sepals.

The Corolla is usually the showy portion—the attraction of the flower. The pieces of the corolla are called petals. The sweet fluids of the plant are here concealed.

These parts—the calyx and corolla—are known as the floral envelopes, or “perianth.” The tulip has one whorl only, and it is called the envelope.

The calyx sometimes falls before the flower is full blown, as in the poppy. Its lower portion is the “throat,” and the shape of the organ varies, as will be seen by the illustrations.

The sepals are usually three to five in number. The poppy has two, and the well-known wall-flower four free—that is, disunited—sepals. The primrose possesses five. The calyx is the outside rim of all, and we may thus remember it, because its sepals alternate with the petals of the corolla. The petals may be formed cup-fashion, as in the lily of the valley, and here we have these sepals and petals in groups of three each.

The petals differ from ordinary leaves, and in them we find all the beautiful tints and the odour we imbibe from blossoms. The forms of corolla correspond to those of the calyx, and are called by the same names. But when corollas are absent the petals of course cannot provide the necessary colours for the flower. Then the calyx is gifted, and the sepals are brilliant. Thus Nature provides for everything.

Corollas are found with five or ten petals, and sometimes with three, six, and nine—the numbers always doubling or adding the original number. There may be four petals or eight, as in the “tetramerous” corolla (fig. 771). Instances of others are illustrated, and a plant whose petals, sepals, and stamens are numerically equal, or are multiples of each other, are termed “symmetrical.” The “regular” flower does not vary much, as the petals are of the same size and shape, but there are many “irregular” flowers—as the pea—in which portions of the calyx or corolla are of different shapes. The “labiate” and the “campanulate” are illustrated in figs. 774, 775, including the convolvulus and the snap-dragon. These are but a few examples of an almost endless diversity. The “regular” flowers—exemplified in the buttercup and convolvulus—always present the same figure to the observer.

To the petals the beautifully-varied colours of plants are due, and though it is not possible to enter upon the subject here, we may conclude that the various beauties of the colours of flowers are owing to light and air acting upon the various “colouring matters” contained in the plant. Seeds planted in a dark cellar will spring up pale; admit light, and they will become green, for light thus acts upon the chlorophyl. But the flowers of the plant are not so dependent upon light, as can easily be proved. Many interesting experiments have been made upon flowers by acids and gases.36

The Stamens are the next in order for our consideration. They are found within the petals (or the calyx if no petals be present). Stamens vary very much in different plants both in number and general features—but, as in the case of petals, they keep, as a rule, to certain numbers and doubles of them. The stamen consists of two portions—a lower, thread-like part called the filament, and an oblong bag or head, termed the anther. This contains a powdery matter called pollen, and is the essential part of the stamen. The filament, which corresponds to the petiole of the leaf, may be absent, in which case the anther is called sessile. A lily will show the stamens perfectly, the anther being prominent in many other plants also, such as daffodils and fuchsias.

The stamens are very important organs with regard to the classification of plants—for number, length, and position, whether free or united, are all characteristic features. The length of filaments is always the same in the same kind of plant, and therefore is a very palpable test.

The anther contains the pollen, a powdery matter, usually yellow-coloured, but sometimes also red, brown, violet, or green-coloured. Pollen-grains vary from 1/20 to 1/300 of a line in diameter. Under a powerful microscope they appear as ellipsoidal, or sometimes spherical, triangular, polyhedral vesicles, filled with a granular semi-fluid matter. To effect fecundation, the pollen-grains must come into contact with a certain part of the plant which is intended to receive them, and which is called the ovule, and is found in the fourth or innermost verticil of the flower, the pistil. Of the further development of the ovule, we shall have occasion to speak in the paragraph treating of the seed.

At the proper time the anther opens and discharges its contents, the pollen-grains, some of which reach the place of their destination. The position of the stamens to the pistil is usually such that the latter can readily receive the pollen-grains. In many plants, however, the stamens are too short to reach the pistils; or the two essential organs of reproduction are in separate flowers, or even on different plants. In such cases, the conveyance of the pollen from the anthers to the pistils is effected by the agency of the wind, or by that of insects, and more particularly by the bee. If the anthers are removed from the flower previously to their opening, no fruit is produced.

Varieties of flowers and fruits are produced artificially, by shaking the pollen of one plant upon the flowers of another, deprived of the stamens. Many esteemed sorts of stock-gilliflowers and pinks have been produced in this way.

The pistil constitutes the fourth and innermost whorl, and occupies accordingly the centre of the flower and the apex of the axis, whose growth is terminated with the production of the fruit.

The pistil also is formed by one or several modified leaves, called carpels, in this part of the flower, and which exhibit a more marked resemblance in colour and structure to the ordinary leaves than the stamens and petals do. The formation of the pistil from the leaf may be considered to proceed in this manner: that the edges of the leaf are folded inwards and unite, whilst the mid-rib is prolonged upwards (fig. 776A). The place where the margins of the folded leaves are united is called suture or seam (ventral suture, in contradistinction to the mid-rib, which is called the dorsal suture); and it is here that the seed-buds or ovules are developed.

The pistil consists of two parts—viz., the ovary or germen, which contains the ovules or young seeds, a, and the stigma, b, either placed upon the ovary, or upon the style, or stalk, which is between the stigma and the ovary.

A pistil may be of one carpel (simple), or of more than one (compound). The carpels or the carpellary leaves are the “ovaries.”

The pistil is a very important test for the classification of plants; some trees have no pistils, and the ovules are consequently naked. Such plants are called gymnospermÆ. The coniferÆ (firs and pines) are thus recognizable, and the position of the ovule is very much that of the ordinary bud.