64 
Wenham, on the Vegetable Cell. 
secondary layers, and the appearance of other constituents, 
as starch, chlorophyll, &c. 
The sooner the term " primordial utricle," as applied to 
the active nitrogenous fluid, or protoplasm, flowing round the 
interior ofthe cell-cavities, is discarded the better, for a clear 
understanding of its all-important properties as the formative 
principle. If even a viscid fluid can be endowed with the 
properties of a membrane, it is not at all times so in this 
case, as it frequently collects in the form of clots, or nuclei 
(as some might term them) ; thus changing its name and 
appearance perhaps several times during the course of a day. 
The specimens drawn for illustrating my last paper origin- 
ated in a plasma so homogeneous and free from all extraneous 
matters, that the cell-cavities were clear from first contents ; 
in fact, this is mostly the case with Anacharis and some other 
aquatic plants ; the cellulation occurring in a mass of proto- 
plasm nearly pure ; but this is not so in other instances. 
What I have already said of cellular formation might serve 
as a guide to the principle to which my investigations have 
led me, but it may now be proper to notice some frequent 
variations, which at first sight might not appear reconcilable 
to my views : I refer to tissues originating in a mass of cells, 
not hollow at their commencement, but with their cavities 
completely filled with contents (and hence I have always 
hesitated in making use of the general term "vacuoles"). 
This condition is easily observable in some leaves and germi- 
nating seeds, where the formative substance contains a larger 
quantity of extraneous matter ; under such circumstances the 
process of cellulation is in no way different, for relieving the 
mind from the task of attempting to reconcile the theory of 
the subdivision of an unity (and the relationship of mother 
and daughter cells "), and admitting the principle of a simulta- 
neous development of cells, the denser granulated material of the 
original plasma, in its first stage of cellulation, is shown to 
arrange itself in the form of irregular squares, trapeziums, or 
oblong figures, partitioned off by thick divisions of more 
transparency and consistency. This is the true protoplasm, 
which has separated from its solid admixtures, or expanded 
from centres, as it were, to form the cell walls, a process to 
which Dr. Carpenter has so appropriately applied the term 
" differentiation ; " * but it must not be supposed that these 
* This term is also explanatory of the formation of the simplest types 
of shell, which have arisen from a plasma containing calcareous matter. 
The " sarcode " (analogous in vital properties to vegetable protoplasm) 
having separated into somewhat irregular divisions, and formed a mem- 
brane between the nucleated and consolidated calcareous matter, producing 
a rude cellular structure. In some more perfect developments of shell 
