584 CONSERVATIVE ORGANS. . [LECT. X. 



axis, the whole length of the leaf, giving off in its 

 course a few thread-like branches only at consi- 

 derable intervals; and as this vascular fasciculus 

 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 succulent leaves ; and are less necessary 

 than in membranaceous leaves ; for, as succulent 

 leaves either exhale very little moisture, or absorb 

 a considerable quantity from the atmosphere by 

 their surfaces, the nutriment of the plant, in the 

 first case, is sufficient although the fluids taken up 

 by the roots be comparatively scanty ; and, in the 

 second, it is supplied, independent of that which 

 may be furnished by the roots, by cutaneous ab- 

 sorption. 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, subdi- 

 vide, and inosculate as in thin leaves ; and the 

 proper or returning vessels accompany and sur- 

 round the spirals in all their divisions. In the suc- 

 culent leaves of dicotyledonous plants, also, we 

 find the same system of tubular cells, between the 



