112 BOTANY AND PHARMACOGNOSY. 



the base to the apex is called the midrib, while the secondary 

 veins which arise from it and run more or less parallel to the 

 margin are sometimes spoken of as ribs and may be likened to the 

 plumes on the shaft of a feather. 



In other cases several large veins arise at the base and diverge 

 toward the margin, giving rise to palmately-veined leaves, as 

 in the leaf of maple. There are still other types, as in cinnamon 

 (Fig. 146) which is said to be rib-netted, etc. 



Surface of Leaves. — In addition to the markings of leaves 

 due to veining there are certain other characters which serve 

 to distinguish them. Hairs are of frequent occurrence on leaves, 

 being generally most abundant on the dorsal surface, especially the 

 veins, and various terms having reference to the kinds of hairs 

 have been applied to leaves (page 210; Figs. 283, 284, 285). 



Texture of Leaves. — Leaves also vary in texture. A thin 

 pliable leaf is called membranous ; one which is thick and leathery, 

 coriaceous ; and one which is thick and fleshy, succulent, as that 

 of the century plant and Aloe (Fig. 130). 



Forms of Leaves. — The leaves of plants exhibit an almost 

 innumerable variety of forms (Fig. 78) ; even on the same plant 

 there are not infrequently several forms, as in Viola tricolor and 

 sassafras (Fig. 73) ; even the two sides of the same leaf may vary, 

 as in Hamamelis (Fig. 264) and Begonia, when it is known as an 

 inequilateral or asymmetric leaf. It frequently happens that the 

 lower leaves on a shoot are lobed while the upper ones are entire, 

 or some of the leaves may be sessile and others petiolate. Many 

 of the terms used in ordinary language in describing the forms of 

 objects are applied here also, as linear, lanceolate, oblong, ellip- 

 tical, spatulate, wedge-shaped, etc. 



Apex of Leaf. — A number of descriptive terms are employed 

 in describing the apex of the lamina, as acute, when the form is 

 that of an acute angle ; obtuse, when the angle is blunt ; acumin- 

 ate, when the angle is prolonged; truncate, when the end of 

 the leaf appears to be cut off ; retuse, when it is slightly notched 

 at the apex ; obcordate, when the notch is pronounced ; emar- 

 ginate, when the degree of notching is between retuse and 

 obcordate. Sometimes the apex appears like the continuation of 

 the midrib, \\hen it is termed cuspidate or mucronate. 



