sun 



Los 



THE SHAPES OF LEAVES. 



141 



mixed symmetry occurs under conditions that are interme- 

 diate. A more marked degree of the same relation is pre- 

 sented in the leaf of the Lady's Mantle, Fig. 215. And 



then in the Sycamore and the Vine, we have a cleft type of 

 leaf in which a decided bilateralness of form co-exists with 

 a decided bilateralness of conditions. 



The quite simple leaves to which we now descend, exhibit, 

 very distinctly, a parallel series of facts. "Where they grow 

 up on long and completely-independent foot-stalks, without 

 definite subordination to some central vertical axis, the 

 leaves of water-plants are symmetrically peltate. Of this 

 the sacred Indian-bean, Fig. 216, furnishes an example. Here 

 there is only a trace of bilateralness in the venation of the 

 leaf, corresponding to the very small difference of the con- 

 ditions on the proximal and distal sides. In the Victoria 

 regia, Fig. 217, the foot-stalks, though radiating almost 

 horizontally from a centre, are so long as to keep the leaves 

 quite remote from one another ; and in it each leaf is almost 

 symmetrically peltate, with a bilateralness indicated only by 

 a seam over the line of the foot-stalk. The leaves of the 

 Nymphxa, Fig. 218, more closely clustered, and having less 

 317 z* s 



room transversely than longitudinally, exhibit a marked 

 advance to the two-sided form ; not only in the excess of 

 the length over the breadth, but in the existence of a cleft, 



