CHAP. II. 
EPIDERMIS. 
49 
live under water. Its usual character is that of a delicate 
membrane, but in some plants it is so hard as almost to re- 
sist the blade of a knife, as in the pseudo-bulbs of certain 
Orchidaceous plants. The most usual form of its reticula- 
tions is the hexagonal (Plate III. fig. II.): sometimes they 
are exceedingly uncertain in figure ; often prismatical ; and 
not unfrequently bounded by sinuous lines, so irregular in 
their direction as to give the meshes no determinate figure 
{Juj. 5 .). 
Botanists were formerly not agreed upon the exact nature 
of the epidermis ; while some inclined to the opinion that it 
is an external layer of cellular tissue in a compressed state, 
others, among whom were included both Kieser and Amici, 
considered it a membrane of a peculiar nature, transversed 
by veins, or vasa lymphatica. 
By the latter it was contended, that the sinuous direction of 
the lines in many kinds of epidermis is incompatible with the 
idea of any thing formed by the adhesion of cellular tissue ; 
that when it is once removed, the subjacent tissue dies, and 
does not become epidermis in its turn, and that it may often 
be torn up readily without laceration. 
On the other hand, it was replied, that the reticulations of the 
epidermis are mostly of some figure analogous to that of cel- 
lular tissue, and that the sinuous meshes themselves are not so 
different as to be incompatible with the idea of a membrane 
formed of adhering bladders. We are accustomed to see so 
much variety in the mere form of all parts of plants, that an 
anomalous configuration in cellular tissue should not surprise 
us. The lines, or supposed lymphatic vessels, are nothing 
more than the united sides of the bladders, and are altogether 
the same as are presented to the eye by any section of a mass 
of cellular substance. It is certain that the epidermis cannot be 
removed without lacerating the subjacent tissue, with however 
much facility it may be sometimes separable : on the under 
surface of the leaf of the Box, for instance, there has plainly 
been some tearing of the tissue, before the epidermis acquired 
the loose state in which it is finally found. 
There is now no anatomist to be found who doubts the fact 
of epidermis being cellular tissue. In many plants the cel- 
E 
