MOHL ON THE STRUCTURE OF THE VEGETABLE CELL. 97 
formation of the nucleus of the cell is always subsequent to the 
origin of the cells ; I cannot, however, agree with this statement. 
It is quite true that frequently, and especially in the roots of 
Monocotyledons (on the observation of which Unger founded 
this view), the nuclei do not attain their full size and shape for 
a long time after the formation of the cell, but they may be 
proved to exist along with the nucleolar granules even in the 
youngest cells, by the use of iodine, and considering the analogy 
of those cases in which the formation of the cell is more clearly 
to be traced, as in hairs, must be regarded as the organ pre- 
ceding the cell. On the whole I am inclined to consider the 
foregoing observations as confirmatory of Schleiden’s theory 
respecting the formation of cells*; on two points, however, I 
cannot but differ from Schleiden’s views. One refers to the 
connexion existing between the nucleus and the nascent cellular 
membrane. Schleiden’s says that the latter grows out from the 
nucleus in such a manner that it is applied upon it like a watch- 
glass, and the nucleus forms part of the developed cell itself; 
to me, on the contrary, the cell membrane always appears to 
surround the nucleus, in the form of a closed vesicle, and in 
many cases to lie at some distance from it, even at their first 
origination, so that in this case the nucleus is by no means in 
immediate contact with the cell-membrane. The second point 
relates to the nature of this primary cellular membrane. Ac- 
cording to Schleiden’s view this is the membrane which forms 
the future external membrane of the cell; to me it appears to 
be that which has hitherto been described as the primordial 
utricle. If, for instance, we examine young cellular tissue, the 
nucleus will be found in particularly close connexion with the 
primordial utricle. Hither, and this is usually the case, (occurring, 
for instance, without exception, in the cambium layer,) the nu- 
cleus lies immediately on the primordial utricle, and separates 
with it from the permanent cell-wall, or threads proceed from 
the mucilaginous coating of the nucleus, which connect it 
with the primordial utricle, so that frequentiy it is suspended, 
as in a cobweb, in the middle of the cell; this is most beau- 
‘tifully seen in Zygnema, in which Schleiden mistook these 
threads for currents of sap; in other cases the whole space be- 
tween the nucleus and the primordial utricle is filled with vesi- 
cular formations, whose walls consist of the same mucilaginous 
* See Scientific Memoirs, vol. ii. p. 281. 
VOL, IV. PART XIII. H 
