LECT. X.] ANATOMY OF LEAVES. 595 



that we certainly know of the subject is, that the 

 fluids are transmitted from cell to cell, through 

 every part of the vegetable system, although the 

 structure by which this is accomplished remains 

 undiscovered. 



Whatever may be the mode in which the cells 

 communicate with one another, their contents are 

 more or less fluid or solid, according to their situ- 

 ation in the thickness of the leaf. Thus, in thin 

 leaves the cells near the inferior disk are more trans- 

 parent, owing to their contents being more fluid 

 than those near the upper disk ; but in both we per- 

 ceive a number of granules, which are more opaque 

 and of a deeper green, as the cells containing them 

 approach the upper disk. In succulent leaves, and 

 those which maintain a vertical position, the 

 opacity and green colour of the granules, are the 

 same towards every face of the leaf; but they are 

 generally colourless in its centre. In the cells, 

 also, of some leaves, regular crystallized salts are 

 found; and in others the fluids are tinged of dif- 

 ferent hues besides green; in which cases the 

 leaves themselves display the same hues on one 

 or both surfaces. 



The size of the cells varies in different leaves ; 

 in some, even when examined under the most 

 powerful glasses, they appear like the smallest 

 vesicles ; while, in others, they are so large as to 

 be perceptible to the unassisted eye. 



QQ2 



