CHAP. I. 
OF THE ELEMENTARY ORGANS. 
3 
It is the opinion of some anatomists that of membrane and 
fibre, the latter only is the basis of the tissue of plants : fibre 
itself being a form of membrane. But we find both the one 
and the other developed in many of the most imperfectly 
organized plants, such as Scleroderma and other fungi, and 
it is difficult to conceive how that can be a mere modification 
of membrane which is generated independently of it, which 
has no external resemblance to it, and which in many cases 
is obviously something superadded. 
Membrane varies in its degree of transparency, being occa- 
sionally so exceedingly thin as to be scarcely discoverable, 
except by the little particles that stick to it, or by its refrac- 
tion of light, but in ferns, some fuci, and other cryptogamic 
plants, it is brown from its first birth : according to Roper it 
is green in Viscum album ; Link says it is green in the leaves 
of Ruellia Sabiniana and the petiole of Cycas revoluta ; and 
Meyen mentions its being orange coloured in the petiole of 
many tropical Orchidaceae. It is always excessively thin 
when first generated ; and whatever thickness it afterwards 
acquires must be supposed to be owing to the incorporation 
or incrustation of secreted matter. This was first observed 
by Mohl in Palm-trees, where he found a successive addition 
of strata to the lining of the cavities of the cells; and is appa- 
rently an universal occurrence where membrane becomes 
thickened. But the matter added to membrane is often 
so homogeneous as to offer no trace of its being deposited 
concentrically, even when examined by the most powerful 
microscopes, and I am by no means able to discover the 
regular lines upon its section which are represented so 
uniformly by the German anatomists. There can, however, 
be no doubt that the membrane of the woody tubes of the 
liber is in many plants 
thickened successively by 
the deposit inside of con- 
centric layers of sediment- 
ary matter, as may be seen 
inCastanea vesca (JigA.a), 
and Betula alba, and in the 
B 2 
