Mule.—A sterile (seedless) hybrid.
GENERAL REQUIREMENTS.—In order to understand the methods of pollination, the reader must be able to recognize the parts of the flower. The fuchsia, [Fig. 90], shows the parts distinctly. The open flower, on the right, contains four well-marked series of organs. The first series is composed of four narrow and leaf-like parts or sepals, collectively called the calyx. Borne upon these is the corolla, made up of four blunt and variously colored petals. The next series comprises eight slender stamens or male organs (S). The thread-like portions or stalks of these are the filaments and upon them are borne the anthers. The anthers contain the pollen. The last and innermost series is a pistil or female organ (P). The pistil is made up of three parts: the ovary, which develops into the seed-pod, the style or slender portion, and the stigma, or enlargement at the end. The ovary in this case is the oblong body borne at the base of the flower and upon which the other parts stand. The style runs through the flower to the ovary.
[Fig. 90]. Parts of the Flower.
The modifications of the flower are numberless, both in form and number of parts, but these four series of organs—the calyx, corolla, stamens and pistils—always comprise a complete flower and they are arranged in the order named. A perfect flower is one which contains both stamens and pistils without any reference to the surrounding or leaf-like organs. Many flowers are imperfect or contain only one sex. When the sexes are borne in different flowers upon the same plant, the species is said to be monœcious; and when they are borne upon different plants the species is diœcious. Sometimes the inflorescence is mixed, some flowers being perfect, some staminate and some pistillate, all upon the same plant; such species are polygamous. Most garden plants have perfect flowers. Many nut-bearing trees are monœcious, as walnuts, butternut, hickories, chestnuts, hazels and filbert and oaks. Some of the composite plants are also monœcious, the large head bearing staminate flowers in one part and pistillate in another. Pumpkins and squashes are monœcious and so are most varieties of melons. [Fig. 91] shows a pistillate pumpkin flower with the ovary or young pumpkin below, and [Fig. 92] a staminate flower which lacks the enlargement below. Among diœcious species may be mentioned the willows and poplars.
Fig. 91. Pistillate Squash flower.
The ovary contains the ovules. When these are acted upon or fertilized by the pollen they develop into seeds. The pollen falls upon the stigma or upper extremity of the pistil, and each grain germinates and sends a tube down through the style to an ovule. The stigma is a slightly roughened soft surface, and when it is “ripe,” or ready to receive the pollen, it becomes slightly moist or sticky. In most plants the stigma is merely a circular expansion of tissue ([Fig. 97]), but sometimes it is divided into lobes and the lobes remain closed until it is ready for the pollen. The fuchsia stigma is composed of four lobes, which are closed in [Fig. 90]. [Fig. 93] shows the two-lobed stigma of the trumpet-creeper or tecoma before the flower is ready for pollination. [Fig. 94] shows the stigma open, in condition to receive the pollen. In these flowers the stamens are hidden in the tube of the corolla.