OF LIVING FORMS; OR, MORPHOLOGY. 83 



decidedly unsymmetrical, the superior half of each 

 being smaller than the inferior. It appears as if the 

 upper edge of the leaflet had been trimmed. If now 

 we take a leaf at an earlier stage of its development, 

 the cause of this difference in form, or, at least, one 

 of its causes, will be evident. Fig. 8 shows the bud 

 of a similar leaf before it has Fig. 8. 



completely unfolded. The dif- 

 ferent leaflets are evidently not 

 similarly circumstanced: the la- 

 teral' ones are so folded that 

 while their lower halves are free, 

 their superior halves are in contact with the cen- 

 tral leaflet and with each other, and so are im- 

 peded in their growth. The central leaflet, lying 

 equally between them, expands equally on each 

 side. The common strawberry leaf shows the same 

 form, arising in the same way. 



If we consider the leaf further, we perceive, 

 however, that not only are the leaflets on the sides 

 modified in their form by the conditions under which 

 they have grown, but that the central one is modi- 

 fied also in not less degree. Evidently the lower 



62 



