94 



MORPHOLOGY OF LEAVES. 



there are three, five, seven, or sometimes more ribs of equal 

 strength, the central being the midrib, and each with its system 

 of veins which ramify and form meshes in the interspaces. Here 

 the whole wood}' portion of the leaf divides equally into a num- 

 ber of parts upon leaving the petiole or entering the blade. The 

 ribs there commonly diverge more or less in a palmate or digitte 

 manner (i. e. like outspread fingers of the hand, or the claws of a 

 bird, or like radii of more or less of -a circle) : so, in the corre- 

 lation of outline and venation, this class of veining goes with 



roundish circumscription. This is not so true, however, in a 

 special case, viz., where the ribs, however divergent below, curve 

 forward and all run to the apex of the blade, thus imitating the 

 parallel- veined system, as in Rhexia and generally in the family 

 of which that genus is the single northern representative. 1 



180. Forms as to Outline, &c. DeCandolle conceived the shape 

 of leaves (both the general circumscription and the special con- 

 figuration) to depend on the distribution of the ribs and veins, 

 and quantity of the parenchyma in which these were outspread, 

 a too mechanical view, and not conformable to the history of 

 development. This proves that the framework is adapted to the 

 parenclryma, which grows and shapes the -organ in its own way, 

 rather than the parenchyma to it. It were better to say that the 



1 In Linnaean terminology, palmate and digitate referred to particular out- 

 line only, and were separately used to denote extent of division, palmate, not 

 divided down to the petiole, digitate, when divided, like the claws of a bird, 

 quite down the base. DeCandolle generalized the use of the former term, 

 and ever since the two have been used interchangeably. 



FIG. 158-166. Various forms of simple, chiefly palmately veined leaves. 



