BARK. 
113 
the surface of every vegetable. It is also called the cuticle , a name 
which anatomists have given to the external covering of the animal 
body. There is a striking analogy between animal and vegetable 
cuticle or skin, in the animal it varies in thickness from the deli- 
cate film which covers the eye, 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. 
In the birch you may see the cuticle or outer bark peeling olf in cir¬ 
cular pieces; it seems not to be endowed with the vital principle, and 
in this respect differs from all other parts of the plant. The cuticle 
serves for protection from external injuries, and regulates the pro¬ 
portion of absorption and perspiration through its pores. It is trans¬ 
parent as well as porous, so as to admit to the cellular integument 
the free access of light and air, while it excludes every substance 
which would be injurious. 
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, ( Eguise - 
turn,) the quantity of silex is such, that housekeepers find it an ex¬ 
cellent 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 indestructible. The cuticle is 
sometimes, like the skin of animals, clothed with wool or down, and 
it then becomes an important security against the effects of heat 
and cold. The leaf of the mullein has its cuticle covered with a 
kind of wool; the pericarp of the peach lias a downy cuticle. 
2d. Cellular Texture , is situated beneath the epidermis or outer 
skin of the bark ; it is filled with a resinous substance, which is 
usually green in young plants. This cellular layer possesses glands, 
which, when submitted to the action of light, carry on the'process of 
decomposing carbonic acid gas, by retaining the carbon and evolv¬ 
ing the oxygen gas. The cellular integument envelops branches, 
as well as trunks of trees, and herbaceous stems; it extends into 
roots, but there it neither retains its green colour, nor decomposes 
carbonic acid gas. It is the seat of colour, and in this respect ana¬ 
logous to the cutis, or true skin of animals, which is the substance 
situated under the Giiticle, and is black in the Negro, red in the 
Indian, and pale in the American. In the leaves of vegetables, the 
cellular integument occupies the spaces comprised between the 
nerves, and is of a green colour; in flowers and fruits it is of various 
colours. The cellular substance of some aquatic plants is filled with 
air; in the pine, sumach, &c., it is filled with the proper juices of the 
plant. 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. 
The petals of flowers are almost entirely composed of cellular 
texture, the cells of which are filled with juices fitted to refract and 
reflect the rays of light, so as to produce the brilliant and delicate 
teints which constitute so great a portion of their beauty. The fuci, 
Uses of the eperdimis, or cuticle—Cellular texture—Glands of the cellular integu¬ 
ment—Cellular integument in roots—The seat of colour—Cellular integument in 
leaves, &c.—In aquatic plants—How renewed in the trunks of trees—Found in’the 
petals of flowers, &c. 
10* 
