110 LEAF-ARRANGEMENT. 



be opposite, because if, other things remaining the 

 same, the leaves of the Sycamore were alternate, 

 the sixth leaf would require an inconvenient length 

 of petiole. 



Perhaps it will be said that the Plane-tree, which 

 has leaves so much like a Maple that one species 

 of the latter genus is named after it (Acer plata- 



FIG. 29. ACER. 



noides, Fig. 29), has, nevertheless, alternate leaves. 

 In reality, however, I think this rather supports 

 my argument, because the leaves of the Plane, 

 instead of being at right angles to the stem, lie 

 more nearly parallel with it. Moreover, as any one 

 can see, the leaves are not arranged so successfully 

 with reference to exposure as those of the species 

 we have hitherto been considering, perhaps be- 

 cause, living as it does in more southern localities, 



