Development, and Structure of the Vegetable Cell. 285 
filled with secretion-vesicles ; and oecasionally I succeeded, by 
adding a thin endosmotic medium, in separating the two, not 
only from the wall of the mother cell, but also from one another ; 
they contained all the chlorophyll present ; and by the plan pur- 
sued the two endogenous membranes of the mother cell also be- 
came somewhat detached from each other. 
In other joint-cells of the same individual, two young cells, 
alike in dimensions and position to those above described, were 
also present; but these could not be separated, by a similar 
proceeding, from one another, nor could the two endogenous 
membranes of the parent joint-cell be detached, or the existence 
of two superimposed cells be any longer distinguished with 
certainty. By the endosmotic current, however, a delicate 
daughter cell was detached from the thickened membrane of 
the new joint-cells, which was then recognized as the true 
immediate envelope of the endogenous secretory material. 
These joint-cells therefore constituted a somewhat more ad- 
vanced phase of development, as indicated also by the incipient 
thickening of their primary membrane. 
As, in the cells just described, secretory matters occur not 
within the now rather thickened primary cells, but, as usual, 
only within the secondary cells, it might seem doubtful whether 
the outer membrane which was in course of thickening does 
actually represent an independently existing cell, or whether it 
might not probably be only an external thickened layer, trans- 
formed into cellulose, of the original cell-membrane, of which 
the remaining portion constitutes the inner, delicate, and pro- 
bably still nitrogenous membrane. 
In opposition to this view, which is by no means destitute of 
probability, and would give countenance to Mohl’s theory that 
the inner secondary cell is of the nature of a primordial ve- 
sicle, several conclusive facts may be adduced. In the first 
place, it may be assumed, from the conditions of development 
above described (p. 282) and represented in PI. VII. fig. 63, after 
treatment with glycerine, that here also the primary cell origin- 
ally, or before the commencement of the thickening of its walls, 
contained secretory materials, then perhaps only in a fluid state, 
although these, at the time of observation, occurred within 
the secondary cell. A still more valid argument, though cer- 
tainly resting only on analogy, is furnished by another develop- 
mental phase observed by me, wherein the primary cell-wall, 
instead of growing inwards so as to form the well-known annular 
fold, in the northal mantier , produced (as seen in fig. 49) a fold 
extending downwards between the cell-walls of the mother and 
daughter cells. 
This interesting condition was met with in several joint-cells 
