164 



THE LEAVES. 



it is termed, is produced at the base of the leaf, which, taken in 

 connection with the general form, gives rise to such terms as cor- 

 date or heart-shaped (Fig. 191), reniform or kidney-shaped (Fig. 

 202), &c., when the posterior portions are rounded ; and those of 

 sagittate or arrow-headed (Fig. 208), and hastate or halberd-shaped 

 (Fig. 206), when they are produced into angles or lobes. The 

 margins of the sinus are sometimes brought into contact, when 

 they are frequently united ; for whenever soft cellular parts are in 

 close contact at an early period of their development, they are 

 very apt to cohere and grow together. In this case the leaf be- 

 comes peltate, or shield-shaped (Fig. 204) ; the blade being at- 

 tached to the petiole, not by its apparent base, but by some part of 

 the lower surface. Two or three common species of Hydrocotyle 

 plainly exhibit the transition from common radiated leaves into the 

 peltate form. Thus, the leaf of H. Americana (Fig. 203) is round- 

 ish-reniform, with an open sinus at the base ; while in H. inter- 

 rupta and H. umbellata (Fig. 204), the margins have grown to- 

 gether so as to obliterate the sinus, and an orbicular peltate leaf is 

 produced. In nerved leaves, when the nerves run parallel from 

 the base to the apex, as in Grasses (Fig. 195), the leaf is necessa- 

 rily linear, or nearly so ; but when they are more divergent in the 



middle, or towards the base, the leaf becomes oblong, oval, or 

 ovate, &c. (Fig. 201). In one class of nerved or parallel-veined 



FIG. 202-210. Forms of simple, chiefly radiated- veined leaves. 



