LECT. X.] ANATOMY OF LEAVES. 587 



considerably in density ; but this diversity depends 

 more on the quantity and quality of the juices the 

 cells contain, than on any diversity of structure 

 in the cells. To the same causes, also, may be 

 attributed, in a great degree, the variety of figure 

 which these cells exhibit: for, although they are 

 in some instances globular, or nearly so; and in 

 others triangular ; or more or less regularly hex- 

 agonal ; yet, it is probable, that the majority are 

 originally spheroidal vesicles; and that the va- 

 riations frqm this figure depend on the turgescence 

 of the vesicles, and the consequent compression 

 which must necessarily result from their conti- 

 guity. The hexagonal figure being that which 

 spheroidal vesicles, mutually comprising one an- 

 other, are naturally disposed to assume, we find 

 that a more or less regular hexagon is the most 

 common form of these cells; and this figure is 

 generally more regular in the cells forming the 

 centre of the substance of the leaf, owing to these 

 being there more distended with fluid, than in 

 those towards either of the cuticles. 



But that the diversity of figure in the cells 

 of leaves does not, altogether, depend on me- 

 chanical compression, is evident from the fact, 

 that those towards the upper disk of the leaf 

 often differ in form from those towards the un- 

 der disk; and yet in both these situations we 

 may suppose the compression to be nearly equal. 



