ON LEAVES. 101 
fio a It is termed the cuticle. It adheres closely to the 
epidermis, moulds itself exactly on this membrane, and even upon 
its hairs, to which it forms a sheath, much as the glove does to the 
finger, covering the epidermis, but presenting minute openings of 
great delicacy corresponding at all points with the stomates. 
In the parenchyma of the leaves of the greater number of vege- 
tables, two distinct regions, an upper and a lower, may be observed 
(Fig. 127). In the upper regions, one, two, or three rows ‘of 
oblong cells may be traced AOQQIOOIOOO Oooo 
perpendicularly to the sur- eS EMU are bea hs eis 
face of the leaf, and closely 
pressing one against the 
other, spread out sometimes 
in such a manner as to leave 
between them many air- 
cells, which are generally 
found to correspond with a 
stomates. The lower bed is 
composed of irregular cel- pte 
lules, often naire out Poon: auueoe apenas — =< 
and touching each other only at pee extreme points of their 
branchie, and leaving them numerous air-cells, which communicate 
one with another, forming a sort of spongeous tissue. Amon 
these cells, many are situated immediately upon the epidermis of 
the lower surface, which is riddled with a much greater number of 
stomates than is the epidermis of the upper surface. It is these 
stomates with which the air-cells corre 
These parenchymentous cellules, a. idl are always very 
thin, are filled with globules of the green vegetable fluid to which 
young plants and leaves owe their colour. This chlorophylle is 
found in great quantities and much denser in the upper zone, than 
in the lower and more spongy parenchyma. The aggregate of 
cells thus coloured by the chlorophylle give to the vegetable leaf 
that green and uniform tint which is its characteristic. 
We have noted these peculiarities of organisation, and above all 
the existence of these intercellular meatus or air-cells,—cavities 
which communicate freely between them, and which are thrown 
in connection with the ambient medium by means of the stomatic 
one 
ey 2 
SASS oso 
