THE CUTICLE. 29 
stantly submersed. It may be loosened and detached from 
the leaves after macerating them in water for a day or two. 
74. The epidermis or cuticle has been very carefully exa- 
mined by M. Adolphe Brongniart, who found it to consist 
essentially of two distinct parts, an outer film or membrane, 
extremely thin and delicate, apparently without any marks of 
organic structure, and an interior layer of flattened vesicles 
in close contact with each other, excepting at the extremi- 
ties. The lines or marking on the outer pellicle are pro- 
duced by the cells or vesicles beneath. They are often hexa- 
gonal, sometimes sinous (waving), and frequently have an 
irregular reticulated appearance. This thin membrane has 
_ been observed particularly in the cabbage leaf, and in digi- ” 
talis. At those places where the vesicles are not in contact, 
there are slits in the thin pellicle above, and beneath these, 
peculiar passages or apertures which have been termed 
STOMATA, opening into the ecoemligne spaces between the 
= 
5. Each of these apertures or siocania cancuts oF eo 
on lunate (of the form of the new moon,) or kidney- 
shaped, touching at the extremities, with the concave sides 
towards each other, an oval opening being thus left between 
them. They are in some plants quadrangular. When 
these semilunar vesicles are distended, with moisture or 
otherwise, the opening between them will be very much con- 
tracted or altogether shut. When they are dry and shrivelled 
the aperture will be open and larger in proportion to the 
shrinking of the vesicles. Water, or a moist atmosphere, 
closes the stomata. They are supposed to be open in 
dry weather or during sunshine. The pores or stomata _ 
give free passage to moisture, and, probably, are the medium _ 
through which the important function of respiration is car 7 
Tied on. 
_ 76. The stomata are found chiefly on parts expoand te the 
and which evaporate freely. They are very abundant 
chiefly on the lower surface, and on the petals 
pals of the flower. Roots, fleshy fruits and seeds, 
