24 OF THE CELLULAR INTEGUMEKT. 



and a new cuticle, covering a rew layer of 

 the same succulent matter, is formed under 

 the old one. Annual stems or branches have 

 not the same power, any more than leaves. 



But little attention has been paid to this 

 organ till lately, though it is very universal, 

 even, as Mirbel observes, in Mosses and 

 Ferns. The same writer remarks that *' leaves 

 " consist almost entirely of a plate of this 

 " substance, covered on each side by the 

 " cuticle. The stems and branches of both 

 ♦' annual and perennial plants are invested 

 " with it ; but in woody parts it is dried up 

 *' and reproduced continually, such parts 

 " only having that reproductive power. The 

 ♦* old layers remain, are pushed outward 

 ♦* by the new ones, and form at length the 

 *' rugged dry dead covering of the old trunks 

 ^* of trees.'' 



When we come to consider the curious 

 functions of leaves, we shall find this part 

 to be of the very first importance. In it 

 the principal changes operated upon the juices 

 of plants by light and air, and the conse- 

 quent elaboration of all their peculiar secre-* 

 tions, take place. 



