108 
PHYSIOLOGICAL VIEWS. 
Epidermis^ or cuticle, is the skin of the membrane which 
extends over the surface of plants. There is a striking anal- 
ogy between animal and vegetable cuticle, or skin. In the 
animal it varies in thickness, from the delicate film which 
covers the eje, to the thick skin of the hand or foot, the 
coarser covering of the ox, or the hard shell of the tortoise. 
In the vegetable it is exquisitely delicate, as in the covering of 
a rose-leaf; or hard and coarse, as in the rugged coats of the 
elm and oak. The cuticle serves for protection from external 
injuries, and regulates the proportion of absorption and perspi- 
ration through its pores. It is transparent as well as porous, so 
as to admit to the cellular integument the free access of liglit 
and air, while it excludes every substance which would be in- 
jurious. 
a. It is to the cuticle of wheat, oat, rye, and some of the grasses, that we are 
indebted for straw and Leghorn hats. In their manufacture the cellular texture 
is scraped away, so that nothing remains but the cuticle. It has been ascertained 
that the outer bark of many of the grasses contains silex, or flint ; — in the scouring 
rush {Equisetum), the quantity of silex is such, that housekeepers find it an excel- 
lent substitute for sand, in scouring wood or metals. A peculiar property of the 
cuticle is, that it is not subject to the same changes as the other parts of bodies : 
it is, of all substances found upon animal or vegetable matter, the most indestructi- 
ble. The cuticle is sometimes, like the skin of animals, clothed with wool, as in the 
leaf of the mullein ; the pericarp of the peach has a downy cuticle. 
126. Cellular integument is situated beneath the epidermis 
or outer skin of the bark ; it is filled with a resinous substance, 
usually green in young plants. It envelops the branches, as 
well as trunks of trees, and herbaceous stems ; it extends into 
roots, but there it neither retains its green color, nor decom- 
poses carbonic acid gas. It is the seat of color, and in this 
respect analogous to the eutis^ or true skin of animals, which is 
the substance situated under the cuticle, and is black in the 
E'egro, red in the Indian, and pale in the American. This 
herbaceous envelope of the trunks of trees after a time dries, 
appearing on the surface in the form of a cuticle, and often 
cleaves off ; it is renewed internally from the cambium. 
127. Cortex. — Immediately under the cellular integument, 
we find the true bark, which, in plants of only one year 
old, consists of one simple layer ; but in trunks of older trees, 
it consists of as many layers as the tree has numbered years. 
The cortex is formed of bundles of fibers called cortical vessels. 
The peculiar virtues or qualities of plants chiefly reside in 
the bark. Here we find the resin of the fir, the astringent 
principle of the oak, and the aromatic oil of the cinnamon. 
The inner loAjer of the harh is called the liher ; from Itber.^ a 
book, on account of its fine and thin layers resemliling the 
Epidermis —a. Uses of the epidermis. — 126. Cellular integument. — 127. Cortex- Liber 
