98 MOHL ON THE STRUCTURE OF THE VEGETABLE CELL. 
granular substance as the threads and the immediate envelope 
of the nucleus, and which like the primordial utricle itself are 
coloured yellow by iodine. Even this intimate connexion of the 
nucleus with the primordial utricle must render it more probable 
that the latter is the first cellular membrane than that the outer 
cell-membrane is formed first, and that the primordial utricle 
subsequently insinuates itself between it and the nucleus, sepa- 
rates the latter with its mucilaginous appendages from the ex- 
ternal cellular membrane, and forms around it a new cell-like 
envelope. The point however would be incontestably proved 
by the above-mentioned observations, that two primordial utricles 
lie contiguous in the still undivided cavity of the cell, if indeed 
no illusion was mixed up with those observations. 
Although the preservation of a plant for a long time in spirit 
appears to be the best way of detaching the primordial utricle 
from the cell-wall and rendering it visible, this result may often 
be obtained by a far shorter process. In general it suffices to 
submit the preparation for a few minutes to the action of nitric 
or hydrochloric acid ; the acid is then to be neutralized by am- 
monia, and if the preparation be now coloured by means of iodine, 
the primordial utricle generally presents itself, as beautifully as 
in plants which have been kept a long time in spirit, in the form 
of a vesicle detached from the cellular membrane. It may be 
detected in this way in the cells of leaves in most cases, for in- 
stance, in Vallisneria spiralis (fig. 4), Sanseviera zeylanica, &c.; 
it may also be very clearly demonstrated in the leaves of Mosses 
and Hepatic, viz. in Jungermannia Taylori (fig. 2), in which 
latter the primordial utricle may sometimes be distinctly sepa- 
rated from the cell-walls by repeated drying and re-moistening*. 
The primordial utricle appears to exist, in all those cells of the 
leaves which contain chlorophylle granules, under the form of 
a completely closed vesicle ; this is not so much the case in the 
transparent cells which in some plants, ex. gr. Tradescantia dis- 
color, lie between the epidermis and the green layer, and in the 
cells, not coloured green, which form the middle substance of 
thick fleshy leaves. In the family of the Algz, the cells of 
which contain granular formations during their whole life, the 
primordial utricle does not exhibit the same extent of decay as 
* During the progress of the above observation on Jungermannia, I had 
evidently before me a cell in which the primordial utricle had accidentally se- 
parated from the cell and had swelled out in the water. 
