562 CONSERVATIVE ORGANS. [LECT. X. 



culiar cellular apparatus to be afterwards de- 

 scribed. These appear to be modifications of the 

 two vascular fasciculi already noticed ; having the 

 same structure as the obscure or invisible fascicu- 

 lus, and the accompanying compact bundle of pro- 

 per vessels of the visible costa (see e. e. fig. 13, 

 Plate 10). In a section obtained by slicing the 

 leaf, we find all these fasciculi united by trans- 

 verse threads, forming rhomboidal meshes, si- 

 milar to those which have been already described. 



But although the arrangement of the vascular 

 system of the leaf of Indian Corn, just described, 

 may be taken as a specimen of that peculiar to the 

 leaves of all the Grasses; and to those leaves of 

 monocotyledonous plants which are petiolated, and 

 furnished with longitudinal costse, yet, there must 

 necessarily be many modifications of this arrange- 

 ment. I shall, however, particularly notice one 

 only, that which characterizes very thick and 

 fleshy leaves; such, for instance, as those of the 

 Aloe tribe. 



On the exterior surface of the leaf of the Aloe, 

 and other leaves of a similar character, we per- 

 ceive no appearance of a vascular system ; but on 

 attempting to tear the leaf across, considerable 

 resistance is opposed to the effort, by a number of 

 tough, longitudinal fibres. These constitute the 

 vascular fasciculi ; and in a transverse section of 

 the leaf, we find that they run through its sub- 



