ANATOMY OF LEAVES. 209 



giving off in its course a few thread-like branches on- 

 ly at considerable intervals ; and as this vascular fas- 

 ciculus and its ramifications are situated in what may 

 be termed the pith of the leaf, and are, consequently, 

 imperceptible on its surface, this description of leaves 

 appears to the unassisted eye destitute of vessels. 

 These organs are, indeed, comparatively few in suc- 

 culent leaves, and are less necessary than in those 

 which are membranaceous ; for, as succulent leaves 

 either exhale very lirtle moisture, or absorb a consid- 

 erable quantity from the atmosphere by their surfaces, 

 the nutriment of tue plant, in the first case, is suffi- 

 cient, although the fluids taken up by the roots be 

 Comparatively scanty ; and, in the second, it is sup- 

 plied, independent of that which may be furnished by 

 the roots, by cutaneous absorption. In the leaves of 

 the broad-leaved species of Mesembryanthemum, and 

 in similar succulent leaves, the vessels enter the leaf 

 in several distinct fasciculi ; which diverging, pass on 

 in nearly straight lines, giving off a few bundles only 

 in their course ; but as they approach the apex of 

 the leaf, whatever its form may be, they divide, sub- 

 divide, and inosculate as in thin leaves ; and the prop- 

 er or returning vessels accompany and surround the 

 spirals in all their divisions. In the succulent leaves 

 of dicotyledonous plants, also, we find the same sys- 

 tem of tubular cells, between the pulp and the cuticle 

 which exists in the Aloe of the monocotyledons ; and 

 in the Mesembryanthemum, under examination, we 

 perceive these tubes commencing immediately under 

 the cutis, and terminating generally in the cells of the 

 central pulp ; but sometimes in follicles, which are 

 both very irregular in form, and of very different di- 

 mensions. It is probable that part of the fluid taken 

 up from the atmosphere passes at once into the cen- 

 tral cells, the contents of which are colorless, while 



