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vi organs we must refer the reader to the Glossary. Leaves in the axils of which flower-buds are developed are called bracts; they are frequently of different form to the other leaves of the plant, and are sometimes membranaceous or scale-like.

The leaves of most woody plants in this country drop from the stem in the autumn, or are deciduous; and though the Holly, Pine, and some other trees and shrubs retain their old leaves until the new ones are formed in the ensuing spring, and are consequently evergreen, all our trees change their leaves at some period of the year.

Leaves are arranged in various ways upon the stem; but generally they are alternate, or situated singly at each node, on alternate sides of the stem, or in a spiral manner,—a mode of growth to which there appears to be a general tendency in plants, probably the result of the two movements of lateral and longitudinal growth proceeding at the same time at right angles to each other, in accordance with a well-known mechanical law. In many plants the leaves are opposite, or arranged in pairs on opposite sides of the stem; and in some they are in whorls, a number being situated in a circle round each node. The leaves of climbing plants are often furnished with elongated appendages called tendrils, by which they cling to the stems or other objects near them; the petioles in other cases twine in a similar manner, as in the Clematis of our hedges.

These organs are all employed in preserving the life of the vegetable and fulfilling the various functions of its existence. Their form and appearance are often of great importance in botanical classification, particularly in distinguishing species, but must be considered of secondary value, as regards systematic arrangement, to those organs of reproduction forming the most conspicuous feature of the flowering plants, and upon the characters of which the arrangement and classification of this portion of the vegetable kingdom chiefly depend.