Birds and Nature, Vol. 08, No. 1, June 1900 / In Natural Colors

by Various

The pollen is necessary to enable the flower to produce seeds, but it must be transferred from the anther which produces it to the fourth part of the flower, not yet described, in which the seeds are formed. This transfer of pollen is known as pollination, and the transfer is usually effected in one of two ways, by the wind or by insects. As a rule, also, the pollen made by one flower must be transferred to some other flower to do its work, and sometimes the other flower may be at a considerable distance.

If the pollen is to be transferred by the wind it must be very light and dry, and it must also be very abundant, for the wind is a chance carrier and drops the pollen everywhere in a very wasteful fashion. In such a case the pollen must come down like rain to be sure that some of it strikes the right spot in the right flowers. Occasionally one hears in the papers of "showers of sulphur," which always prove to be showers of pollen carried by the wind from some forest (chiefly evergreen forests) and dropped at random. In the case of pines the minute pollen grains develop wings to assist in the wind transportation.

If the pollen is to be transferred by insects it does not need to be so dry and powdery, or so abundant as in the other case, for the insect passes directly from one flower to another, without any random scattering of the pollen. Only winged insects are used for this purpose, as those which must creep, or rather walk, would brush the pollen from their bodies by rubbing against the various obstructions in the way. The insects most commonly used are the numerous kinds of bees, wasps, butterflies, and moths. These insects visit the flowers for different purposes. The butterflies and moths are after the nectar, while the bees and wasps feed upon the pollen. Visiting insects are therefore often grouped as nectar feeders, and pollen feeders, but in either case they are instrumental in transferring the pollen.

The fourth or innermost part of the lily flower is an organ called the pistil. It stands in the center of the flower and is composed of three distinct regions. At the base it is bulbous and hollow, containing the bodies which are to become seeds. This bulbous region is called the ovary, and the little bodies it contains, which, through the action of the pollen, are to become seeds, are called ovules. Rising from the top of the ovary is a slender, stalk-like part called the style; and at the top of the style is a knob-like region called the stigma.

The most essential region of the pistil is the ovary, for it contains the ovules. Next in importance is the stigma, for it must receive the pollen-grains. The style is of least importance, and therefore is sometimes wanting, the stigma being directly upon the ovary. The duty of the style, when it is present, seems to be to put the stigma into a favorable position to receive the pollen. It must not be supposed that the stigma always resembles a knob-like top to the style. It is really only a surface prepared to receive pollen, so it may be upon the top of the style, or may run like a line down one side of it, or may display itself in some other way.

The pistil of the lily, however, is not a single structure. If the ovary be cut across, it will be found to be made up of three compartments, each one of which contains ovules. Each one of these compartments represents a unit of structure which has entered into the formation of the pistil. These units are called carpels, and the pistil of the lily is made up of three carpels. In this case the three are distinct only in the ovary, and have completely lost their identity in the region of the style. In many relatives of the lily, however, the three carpels are kept distinct in the style region, three styles or a three-parted style appearing upon the ovary.

In some flowers the carpels are kept entirely distinct, each one having its own ovary, style, and stigma. For example, in the buttercup there is a little mound in the center of the flower made up of numerous pistils, each consisting of a single carpel. It is evident, therefore, that a pistil may consist of one carpel or several carpels, and that in the latter case the carpels may be more or less completely united. The sure indication of a carpel is that each carpel bears its own ovules.

In some flowers there is but a single carpel, as in peas and beans, whose pods have developed from a pistil consisting of a single carpel, as is indicated by the single lengthwise set of seeds.

In some plants the flowers do not have all the four parts described above. In some cases the petals may be lacking, the one set of perianth parts represented being regarded as the calyx, although it may look like a corolla, as in the clematis or anemone. Such flowers are said to be apetalous, which means "without petals." In other cases both the calyx and corolla may be wanting, the flower consisting of only stamens and carpels. Such flowers are spoken of as naked.

In other flowers the stamens may be lacking, and as the pistil is the only essential part present such flowers are said to be pistillate. It may be counted upon, however, that if there are pistillate flowers there are also corresponding staminate flowers in which the pistils are lacking and the stamens present. In such cases both staminate and pistillate flowers may occur on the same plant, or they may occur on different plants, so that there may be not only staminate and pistillate flowers, but also staminate and pistillate plants.