Page:British Flowering Plants.djvu/27

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INTRODUCTION

In some cases flowers bearing stamens or pistil grow on the same plant, but separately. Thus, in Maize, the upper, tassel-like flowers contain only the stamens, and the lower only the style and carpels or seed-vessels.

The leaves of which the calyx is composed are called sepals. These may be coalescent, separate, divided, fissured, lobate, dentated, regular or irregular, bilobate, tubular, pitcher-shaped, bell-shaped or campanulate, etc.

The leaves of which the corolla is composed are called petals. Sometimes these are completely separated (fig. 76); or they may be more or less closely united, sometimes forming only a single piece.

When the corolla is united below, and more or less divided above, it is said to be lobated, dentated, or segmented, according to the depth and character of the incisions, and the undivided portion is called the cup or tube.

Soon after the plant has flowered the corolla falls off. It serves chiefly to attract insects, which in many cases are necessary to fertilisation. The stamens likewise differ much in form and structure, according to the requirements of the plant. They are sometimes free, and sometimes conglomerated. At the summit of the stamens stand the anthers, which secrete a dust (generally yellow) called pollen.

Sometimes the stamens are fused into a single tube (fig. 77); sometimes they form three clusters (fig. 78); or, again, they may form a single cluster (fig. 79). In other cases we find six stamens, four of about equal length and two shorter (fig. 80); or four, two long ones and two short ones (fig. 81).

The pistil is composed of the ovary or seed-vessel, the style, and the stigma. The ovary is often more or less divided into segments called carpels. It is generally surmounted by the style, at the end of which is the stigma. In order that seed should be matured, it is necessary for the pollen secreted by the anthers to be transferred to the stigma. Sometimes this is effected automatically, especially in perfect flowers; in other cases the pollen is carried from one flower to