648 



ON LEAF-ARRANGEMENT 



[CH. 



which various spirals are implicitly contained, the conspicuousness 

 of one set or another does not depend upon angular divergence. 

 It depends on the relative proportions in length and breadth of 

 the leaves themselves ; or, more strictly speaking, on the ratio of 



Fig. 327. 



the diagonals of the rhomboidal figure by which each leaf-area is 

 circumscribed. When, as in the fir-cone, the scales by mutual 

 compression conform to these rhomboidal outlines, their inclined 

 edges at once guide the eye in the direction of some one particular 

 spiral ; and we shall not fail to notice that in such cases the usual 



