Development, and Structure of the Vegetable Cell. 385 



filled with secretion-vesicles ; and occasionally 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 theoiy 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 withia 

 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 normal manner, 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 



