112 MOHL ON THE STRUCTURE OF THE VEGETABLE CELL. 
place, as has been mentioned above, the latter view is the only 
one compatible with the deposition of the secondary layers in the 
cells of Jungermannia Taylori, Schotia speciosa, &c.; secondly, 
we can convince ourselves by the examination of the cambium 
layer of Dicotyledons, that the thin wall-structure of the ele- 
mentary organ of this layer is an immediate continuation of the 
reticulation which forms the primary membranes in the older 
portion of the wood. The investigation of this point is fre- 
quently far more difficult than it would at first appear, but in 
Pinus sylvestris any one may convince himself in the most po- 
sitive manner, as in this the cambium cells resist the action of 
sulphuric acid (which was not the case with any other of the’ 
plants I examined), while the secondary layer, both in the liber- 
and ligneous-cells, swells strongly in acid, which renders the 
above-mentioned connexion and similarity of their outer mem- 
brane with the membranes of the cells lying in the cambium 
layer distinctly evident. 
If the representation of the process of cell-multiplication which 
I have above given be in accordance with nature, the septum 
which is developed between two primordial utricles, and sub- 
sequently divides the simple cell into two, would come into im- 
mediate connexion with the primary membrane of these cells 
(since the process of increase in cells usually takes place at a 
period when no secondary membrane has yet been deposited), 
and in this way the connexion of all primary membranes in the 
form of a web would be more simply explained. Whether these 
septa consist of a single homogeneous layer, or of two lamelle, 
is, from their great delicacy, not to be determined with our pre- 
sent microscopes. 
If we assume that the septum consists of two layers, it will 
indeed be most natural to suppose that it is formed by a circular 
folding-in of the primary cellular membrane; in this way would 
be explicable how each cell possesses its own proper membrane, 
and how the intercellular passages and the cavities between the 
dots are formed by the mere retraction of the contiguous cellular 
membranes. If we assume, on the contrary, that the primary 
membrane is common to two cells, and consequently that the 
newly-formed septum is likewise simple, we must admit that 
these cellular membranes subsequently undergo an internal 
change which renders possible a separation into two layers, for the 
purpose of forming intercellular passages and cavities of the dots, 
