CHAPTEE IX. 



THE SHAPES OP LEAVES. 



§ 228. Next in the descending order of composition conn 

 compound leaves. The relative sizes and distributions oi 

 their leaflets, as affecting their forms as wholes, have to be 

 considered in their relations to conditions. Figs. 206, 207, 

 represent leaves of the common Oxalis and of the Marsilea, 

 in which radial symmetry is as completely displayed as the 

 small number of leaflets permits. This equal development 

 of the leaflets on all sides, occurs where the foot-stalks, grow- 

 ing up vertically from creeping or underground stems, are 

 so long that the leaves either do not interfere with one 

 another or do it in an inconstant way: the leaflets are not 

 differently conditioned on different sides, as they are where 

 the foot-stalks grow out in the ordinary manner. How un- 

 likeness of position influences the leaflets is clearly shown in 

 a Clover-leaf, Fig. 208, which deviates from the Oxalis-leaf 

 but slightly towards bilateralness, as it deviates from it but 

 slightly in the attitude of its petiole; which is a little in- 

 clined away from the others borne by the same procumbent 

 axis. A familiar example of an almost radial symmetry 

 along with almost equal relations to surrounding conditions, 

 occurs in the root-leaves of the Lupin, Fig. 209 b. Here 

 though we have lateral divergence from a vertical axis, yet 

 the long foot-stalks preserve nearly erect positions, and 

 carry their leaves to such distances from the axis, that the 

 development of the leaflets on the side next it is not much 

 152 



