102 



indicate the ratio between breadth and length adopted for each 

 group, while the height of the curve is determined by the num- 

 ber of individual leaves in that group. It appears, from the 

 curve, that the normal or common type of leaf is that which is 

 about twice as long as it is broad. The progression from very 









RATIC 



OF BREADTH TO LENGTH 















30 



/ 



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^GAi 



















/ 



(, 





\ 



i2.2i 

















1.65^ 









\ 



r->.% 



M 



ktl_ 



.6^ 





1-1>4 l-l>^ \-m 1-2 1-2M 1-2^2 1-2M 1-3 1-314 l-3.'i 1-334' 1-4 



Figure i. 



broad leaves to the common form is very abrupt, while that 

 toward the long narrow forms, though still abrupt, is somewhat 

 gentler, tending to show that variants toward the long narrow 

 types are more common, at least among the leaves measured, 

 than are those toward the broader forms. 



The shape of a leaf depends chiefly upon the relationship 

 existing between its length and breadth, and upon the position 

 of the broadest part of the blade. Therefore the curve express- 

 ing this relationship is to a certain extent prophetic as to what 

 the predominant shape will be. It indicates that the ovate, 

 obovate, oval, and elliptical leaves are likely to be in the 

 majority. Which of these four forms will, however, predomi- 

 nate depends upon the position of the widest part of the leaf. 

 The accuracy of this forecast is shown by the curve (Fig. 2). It 



