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 larger 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 thickness 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 scarcely 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 
