CHAP. II. 
LEAVES. 
125 
of small green bladders, arranged with little order or regu- 
larity ; but if very thin slices are taken and viewed with a 
high magnifying power, it will be seen that nothing can be 
more perfect than the plan upon which the w'hole structure is 
contrived, and that, instead of disorder, the most wise order 
pervades the whole. Upon this subject I extract the words 
of Adolphe Brongniart : — “ There exists beneath the upper 
cuticle two or three layers of oblong blunt vesicles, placed per- 
pendicular to the "surface of the leaf, and generally much less 
in diameter than the bladders of the cuticle ; so that they are 
easily seen through it. These vesicles, which appear specially 
destined to give solidity to the parenchyma of the leaf, have 
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 ar- 
rangement 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, 
