Page:British Flowering Plants.djvu/16

2 rapidly being exterminated in many places by reckless gathering and uprooting.

Plants are divided into two principal sections: Phanerogamia, or those which produce true flowers and seeds; and Cryptogamia, or those which do not. Flowering plants only are included in the present work. The flowerless plants, including Ferns, Mosses, Seaweeds, Lichens, Fungi, Diatoms, Bacteria, and various other low forms of plant life, may perhaps find place in a later volume of this series.

Flowering plants again belong to two main classes—Dicotyledones and Monocotyledones. In Dicotyledones the seed is divided into two halves, each of which throws up a primary leaf when the seed germinates. In Monocotyledones there is often only one primary leaf, and the general formation of the plant is very different. The former class includes by far the larger number of plants. To the latter belong many more or less bulbous plants, such as Orchids, Flags, Lilies, etc.; many water-plants, like Reeds, Rushes, and Sedges; and the great Order of Gramineæ, or Grasses.

STRUCTURE OF A PLANT

A plant consists of the following principal parts: the roots, the stem, the leaves, the flowers, and the fruit.

The roots are fixed in the ground, to support the plant, but in climbing plants, like Ivy, for instance, we meet with aerial roots, which cling to the bark of trees or other supports. At the extremity of the rootlets we generally find a "root-cap," which protects the growing extremity of the root, and enables it to penetrate hard ground. As the root grows, the root-cap also continues to grow, the portion behind the tip dying off. Behind the root-cap are the root-hairs. Their function is to absorb water containing nourishing salts which have been dissolved from the surrounding soil, and to convey it to the actual roots.

Roots are divided into primary and adventitious. The primary root is formed by the prolongation of the stem downwards, which, when well developed, is termed a tap-root. In many plants (Orchidaceæ,