STRUCTURE.] ANATOMY OF LEAVES. 259 



parenchyma that is applied against it ; it may then be seen 

 that these anastomosing vesicles form a net with large meshes 

 a sort of grating inside the cuticle. It must not, how- 

 ever, be supposed that this structure, which I have remarked 

 in several Ferns, and in a great many dicotyledonous plants, 

 is without exception. In many monocotyledonous and suc- 

 culent plants we have some remarkable modifications of this 

 structure. Thus, in the Lily, and several plants of the same 

 family, the vesicles of parenchyma that are in contact with 

 the lower cuticle are lengthened out, sinuous, and toothed, 

 as it were, at the sides : these projections join those of the 

 contiguous vesicle ; and a number of cavities is the conse- 

 quence, which render this sort of parenchyma permeable to 

 air. An analogous arrangement exists in the lower paren- 

 chyma of Galega. In the Iris, there is scarcely any space 

 between the oblong and polyhedral vesicles which form the 

 parenchyma ; but it is remarked, that the subjacent paren- 

 chyma is wanting at every point where the cuticle is pierced 

 by a stomate. In such succulent plants as I have examined, 

 the spaces between the cellules of parenchyma are very small; 

 but, nevertheless, here and there, there are often larger cavi- 

 ties, which either correspond directly with the stomates, or 

 are in communication with them. The same thing happens 

 in plants with floating leaves, where the stomates placed 011 

 the upper surface correspond with the layer of the cylindrical 

 and parallel vesicles ; in such case there are, here and there, 

 between these vesicles, empty spaces which almost always 

 correspond to the points where the stomates exist, and which 

 permit the air to penetrate between the vesicles as far as the 

 middle of the parenchyma of the leaf." 



Thus much Adolphe Brongniart; who adds, that in sub- 

 mersed leaves there is no cuticle, but the whole consists of 

 solid parenchym alone, in which there are no other cavities 

 than such as are necessary to float the leaves. The observa- 

 tions of Mohl, Meyen, and myself generally confirm this ; 

 but, at the same time, numerous cases exist in which the 

 texture of the leaf has been found to be nearly the same 

 throughout ; in fact, the only circumstance which is found 

 to be uniform in respect to the internal anatomy of leaves is, 



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