Page:British Flowering Plants.djvu/26

12 but they are more usually arranged round the stalk.

When leaves stand at different elevations on opposite sides of the stalk they are called alternate (fig. 73); when they are arranged in pairs, at the same elevation, opposite (fig. 74); and when several are placed at the same height, verticillate or whorled (fig. 75).

Tendrils are regarded as slender branches, or leaf-stalks, which assume a spiral form, and twine round various objects for support (fig. 71). Thorns are either the ends of twigs produced into a sharp point, or similarly modified portions of leaves and leaflets. Prickles are hard, erect portions of the surface of the plant. Thus we find thorns on the Hawthorn and Sloe, but prickles on the Rose, Bramble, and Gooseberry.

Hairs are outgrowths from the superficial cells of the stem, leaf, or root. They are generally tubular. Stiff hairs are called bristles or seta;. When they form a cluster, as in Barley, etc., the cluster is called a beard ; when they contain an irritating fluid, as in Nettles, they are called stings; and when they exude any peculiar secretion, they are called glandular hairs.

Flowers are structures preparatory to the formation of the seed, and in many cases are the most conspicuous parts of the plant.

A perfectly formed flower consists of the calyx, which is generally green; the corolla, which is often brightly coloured; the stamens; and the pistil. In imperfect flowers the calyx or corolla, or both, may be wanting; or they may be replaced by a single cup, called the perianth.

A perfect flower contains both stamens and pistil. Such flowers are called hermaphrodite. Other flowers are called monoecious, and in these only the stamens are developed, in which case they are male flowers; or only the pistil, when they are female flowers.

In some plants the stamens are united with the pistil; others, as said above, have only stamens (as wild Hop and male Hemp); and others, again, only the pistil (cultivated Hop and female Hemp).