Page:First course in biology (IA firstcourseinbio00bailrich).pdf/110

from leaves. As a rule leaves can be distinguished by the following tests: (1) Leaves are temporary structures, sooner or later falling. (2) Usually buds are borne in their axils. (3) Leaves are usually borne at joints or nodes. (4) They arise on wood of the current year's growth. (5) They have a more or less definite arrangement. When leaves fall, the twig that bore them remains; when leaflets fall, the main petiole or stalk that bore them also falls.

Shapes.—Leaves and leaflets are infinitely variable in shape. Names have been given to some of the more definite or regular shapes. These names are a part of the language of botany. The names represent ideal or typical shapes; there are no two leaves alike and very few that perfectly conform to the definitions. The shapes are likened to those of familiar objects or of geometrical figures. Some of the commoner shapes are as follows (name original examples in each class):

Fig. 102.—Linear-acuminate Leaf of Grass.

Fig. 103.—Short-oblong Leaves of Box.

Linear, several times longer than broad, with the sides nearly or quite parallel. Spruces and most grasses are examples (Fig. 102). In linear leaves, the main veins are usually parallel to the midrib.

Oblong, twice or thrice as long as broad, with the sides parallel for most of their length. Fig. 103 shows the short-oblong leaves of the box, a plant that is used for permanent edgings in gardens.