LECT. X.] LEAVES. 543 



from the stem which bears them, and are planted. 

 The young plants produced on such leaves are the 

 lateral progeny of the adult plant, by which its 

 existence is renewed, without the aid of the sexual 

 stimulus; in the same manner as buds are formed 

 on stems and branches, offsets on bulbs, and 

 gems on tubers, to the last of which, indeed, such 

 leaves are closely allied. They possess the same 

 distinct vitality as tubers; for the leaves of Co- 

 tyledon calydnum will produce perfect plants from 

 their serratures, if even worn in the pocket, 

 wrapped in a piece of paper; and, holding, as 

 they do, an intermediate place between tubers 

 and leaves, they might be almost regarded as 

 foliaceous tubers. It may be asked, are the 

 germs of the plants, which rise on the margins 

 of such leaves, coexistent with the origin of the 

 leaves, as is the case with the germs in the eye or 

 gem of the tuber? To answer this question we 

 must have recourse to the microscope ; and on 

 examining with it the margins of those leaves of 

 Cotyledon calycinum, which have not yet become 

 proliferous, we perceive in each serrature a small 

 rough papilla, projecting on the under disk of the 

 leaf; and in a transverse section the cellular 

 matter at this place is seen to be differently ar- 

 ranged from that in the rest of the leaf; and 

 displaying in its centre a small opaque point, 

 from which a vessel extends to the surface of the 



