102 ORGANOGRAPHY. BOOK 1. 



no Other intervals than the little spaces that result from the 

 contact of this sort of cylinder : nevertheless, in plants that 

 have stomates on the upper surface of their leaves, as is the 

 case in most herbaceous plants, and in such as float on the 

 surface of water, there exists here and there among the vesicles 

 some large spaces, through which the stomates communicate 

 with the interior of the leaf. 



This parenchyma is entirely different from what is found 

 beneath the cuticle of the lower side. There, instead of con- 

 sisting of regular cylindrical vesicles, it is composed of irre- 

 gular ones, often having two or three branches, which unite 

 with the limbs of the vesicles next them, and so form a reticu- 

 lated parenchyma; the spaces between whose vesicles are 

 much laroer than the vesicles themselves. 



It is this reticulated tissue, with large spaces in it (to which 

 the name of cavernous or spongy parenchyma might not im- 

 properly be applied), that, in most cases, occupies at least 

 half the tliickness of the leaves between the veins. The 

 arrangement of the vesicles is very obvious if the lower cuticle 

 of certain leaves be lifted up with the layer of 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, however, be supposed 

 that this structure, which I have remarked in several ferns, 

 and in a great many dicotyledonous plants, is without excep- 

 tion. In many monocotyledonous and succulent 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 consequence, which render this sort 

 of parenchyma permeable to air. An analogous arrangement 

 exists in the lower parenchyma of Galega. In the Iris, there 

 is scai'cely any space between the oblong and polyedral vesi- 

 cles which form the parenchyma ; but it is remarked, that the 

 subjacent parenchyma 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 



