MOHL ON THE STRUCTURE OF THE VEGETABLE CELL. 99 
it does in the cells of the stems of the Phanerogamia; it is gene- 
rally very easily found in these plants, and especially in all those 
eases where the cells attain a considerable size. In the Fu- 
coidex, as in Halidrys siliquosa, Furcellaria fastigiata (fig. 19. 
Plate II.), it is distinguished from the colourless cell-membrane 
by its brownish tint, and also by its resistance to the action of sul- 
phuric acid; it is still easier to be detected in the Conferve, and 
particularly in the Zygnemata, in which latter the action of al- 
cohol and tincture of iodine readily effect its separation from the 
cell-membrane. It is more difficult to recognise it in Alge 
possessing minute cells, as in the Ulve, in Bangia atropurpurea, 
&c., as there is far more trouble in distinguishing it from the 
contents of the cell. The same difficulty occurs in the Lichens ; 
the primordial utricle is however to be detected in these, in the 
green round-celled layer, especially in those species with a dense 
leaf-like thallus, as Sticta glomerulifera. The discovery of the 
primordial utricle in this family belongs to Wohler and Knop*, 
who first found it in Usnea. 
We may conclude from the foregoing statements that the pri- 
mordial utricle is very generally distributed, but takes no per- 
manent share in the formation of the cell-wall in the Phanero- 
gamia; but, like the nucleus, is a temporary formation connected 
with the origin of the cell. The question now arises, whether 
the primordial utricle is to be regarded as a cellular membrane, 
or whether it is not rather to be reckoned among the contents 
of the cell and looked upon as a coagulated mucilaginous coat- 
ing on the cellular membrane, for which indeed it has certainly 
been frequently taken, since it has undoubtedly presented itself 
in some cases, as in Zygnema, to every vegetable physiologist, 
without having been regarded by them as a distinct membrane. 
The substance of which the primordial utricle is constituted ap- 
pears to be, if not identical, at least nearly allied to the muco- 
granular substance which usually invests the nucleus as an irre- 
gular mass, and from which run out those mucilaginous threads 
we meet with so often in young cells, since these parts behave 
in the same manner towards iodine and sulphuric acid. So far, 
it is true, we are unable to draw such a distinct line between 
the primordial utricle and its contents as we can between the 
permanent cell and its contents; on the contrary, it would ap- 
pear that the primordial utricle must be considered only as a 
* Geetting. gel. Anz. 1844, p. 22, 
H 2 
