Structure of Vegetables . , I §3 
"Cuticle . — The bark is composed of three parts, the 
epidermis, parenchyma, and cortical layers. The epi- 
dermis, or cuticle, is a thin, transparent membrane 
which forms the external covering of the bark, and is 
composed of fibres crossing each other. By means of 
this membrane, the plant is protected from the injuries 
of the air, and the processes of absorption and perspi» 
ration go on through its pores. It is of a very delicate 
texture on some plants, and coarse and thick on others, 
as on the trunk of the Plane-tree ; readily peais off 
from some, as from the Birch ; and may be separated 
by maceration from others. 
The cuticle is susceptible of extraordinary extern* 
sion ; for, during the growth of the plant from the 
commencement of vegetation, it is stretched over its 
whole surface, without receiving any accession of mat* 
ter, as the connection with the vascular or living part 
of the vegetable body seems to be altogether interrup- 
ted but on the old trunks of most trees, it may be 
observed to crack in all directions, and in many it is 
"entirely obliterated. 
In the Currant-tree, and in the Elder, the Cuticle is 
smooth, and scales off in large flakes ; in the fruit of 
the Peach, and the leaves of the Mullein, it is covered 
with, dense harsh wool ; in the leaf of the White Wil- 
low, it is of *a silky texture ; in the Betony, and some 
other plants, it is extended into rigid hairs or bristles ; 
on the fruit of the Plum, and on many leaves, it is co- 
vered with a dry bluish powder, which repels the drops 
©f rain; in the Cork-tree, the Common Maple, the 
Dutch Elm, and the Constantinople Hazel, the cuticle 
is covered with a singular fungous substance, well 
known as cork ; and in Grasses and Reeds, siliceous 
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