LECT. X.] ANATOMY OP LEAVES. 571 



the leaf, e. being the upper and f. the under 

 disk, the relative situation of the vessels is still 

 more clearly demonstrated. 



We may pause here a few moments to re- 

 mark, that the colour of the juice in the cells of 

 the leaf, is more intense towards the surfaces, 

 while in the centre it is scarcely deeper than that 

 which is contained in the cells of the cutis (e.f.). 

 Is not this probably owing to the sap which is 

 current in the spiral vessels, and which is co- 

 lourless, being given out laterally, and diffusing 

 itself through the cells, in which the change 

 effected by the air and light, that causes the co- 

 lour is produced ? The manner in which the co- 

 lour is diluted as it approaches the limits of 

 the spiral vessels, would authorize such a suppo- 

 sition ; but, wherefore it may be demanded, are 

 the cells immediately under the cutis free from 

 colour ? It is probable, we may reply, that these 

 cells are filled by pure water only, absorbed from 

 the atmosphere; and, consequently, their con- 

 tents are unfitted to undergo those chymical 

 changes to which the sap is subjected in the leaf. 

 But this discussion is premature. 



From this demonstration of the vascular sys- 

 tem in the leaves of monocotyledonous plants, 

 it is evident that a general character, however 

 variously modified in many instances, pervades 

 the whole. The fasciculi of vessels are distinct; 

 they run in directions parallel to one another; 



