THEIR FORMS AND VENATION. 163 



the apex of the petiole into three or more portions or ribs of nearly 

 equal size, which are usually divergent, each giving off veins and 

 veinlets, like the single rib of a feather-veined leaf. Such leaves 

 are termed radiated-veined, or palmately veined ; and, as to the 

 number of the ribs, are called three-ribbed, five-ribbed, seven- 

 ribbed, &c. (Fig. 191, 203, 209). Examples of this form are fur- 

 nished by the Maple, the Gooseberry, the Mallow Family, &c. 

 Occasionally the ribs of a radiated-veined leaf converge and run to 

 the apex of the blade, as in Rhexia and other plants of the same 

 family, thus resembling a parallel-veined or nerved leaf; from 

 which, however, it is distinguished by the intermediate netted 

 veins. But when the ribs are not very strong, such leaves are fre- 

 quently said to be nerved, although they branch before reaching 

 the apex. 



280. According to the theory of De Candolle (275), the shape 

 which leaves assume may be considered to depend upon the dis- 

 tribution of the veins, and the quantity of parenchyma ; the gen- 

 eral outline being determined by the division and direction of the 

 veins ; and the form of the margin, (whether even and continuous, 

 or interrupted by void spaces or indentations,) by the greater or 

 less abundance of the parenchyma in which the veins are distrib- 

 uted. This view is readily intelligible upon the supposition that a 

 leaf is an expansion of soft parenchyma, in which the firmer veins 

 are variously ramified. Thus, if the principal veins of a feather- 

 veined leaf are not greatly prolonged, and are somewhat equal in 

 length, the blade will have a more or less elongated form. If the 

 veins are very short in proportion to the midrib, and equal in length, 

 the leaf will be linear (as in Fig. 198) ; if longer in proportion, 

 but still equal, the leaf will assume an oblong form (Fig. 200), 

 which a slight rounding of the sides converts into an oval or ellip- 

 tical outline. If the veins next the base are longest, and espe- 

 cially if they curve forward towards their extremities, the leaf 

 assumes a lanceolate (Fig. 197), ovate (Fig. 199), or some inter- 

 mediate form. On the other hand, if the veins are more developed 

 beyond the middle of the blade, the leaf becomes obovate (Fig. 

 189), or cuneiform (Fig. 192). In radiated or palmately-veined 

 leaves (Fig. 202-204), where the primary ribs are" divergent, an 

 orbicular or roundish outline is most common, and indeed is uni- 

 versal when the ribs are of equal strength. Some of the ribs or 

 their ramifications being directed backwards, a recess, or sinus, as 



