484 Prof. H. Karsten on the Vegetable Cell. 



When the above-mentioned solvents for a cell-membrane 

 engaged in chemical metamorphosis for the purpose of lignifica- 

 tion are allowed to act upon a septum in process of thickening 

 (fig. 40 a), and a stronger contraction is then induced in one of 

 the two adjoining and adherent daughter cells by the agency of 

 exosmotic fluids, the central and unthickened portion of the 

 septum is torn through, whilst the peripheral walls of the two 

 adherent sister cells remain connected, as indeed was observed 

 although differently interpreted by Mohl (Vermischte Schriften, 

 xiii. 8, 9). 



The chemical and physical actions of the above-mentioned 

 commonly employed reagents upon the substance of plants has, 

 however, been by no means sufficiently studied to enable us, 

 from the changes which they produce upon vegetable tissues, to 

 arrive at any certain conclusions as to the structure of the latter. 

 And our knowledge of the mode of action of these reagents 

 upon the membranes of assimilant cells is especially imperfect, 

 because it is different in each new stage of development of the 

 cell, which is in a constant process of change. 



The intimate knowledge of the anatomical changes which 

 take place in the cell in the course of development must there- 

 fore precede, or at least go hand in hand with, that investigation, 

 the results of which consequently, as yet, are of subordinate 

 value in the appreciation of anatomical conditions. 



The mutual adherence of the constituent cell -membranes of 

 the septum (p. 283), which stands so much in the way of a 

 correct recognition of its true nature, appears to be still more 

 inexplicable, under certain circumstances, in fully developed 

 cells. In such cells the still delicate daughter cells are com- 

 monly separated with great facility from the parent cell by the 

 action of diosmotic fluids. But if .a specimen of Conferva glo- 

 merata be allowed to lie for some time in a dilute aqueous solu- 

 tion of tannin or of ammonia, and an aqueous solution of iodine 

 be then brought in contact with it, not only are the membranes 

 of the secondary cells loosened from those of the primary, but 

 these last also are partially separated from the mother cell, and 

 the enveloping membrane from the included joint-cells even to 

 the very extremity (fig. 41). All the thickened membranes 

 moreover show very clearly the thickening layers, which are 

 either imperceptible or very imperfectly recognizable in the 

 living plant : this is the case especially after their penetration 

 by a solution of gum arable. The delicate membranes of the 

 secondary cells are not, however, detached at both extremities, 

 as in normal states, from the primary cell, but maintain their 

 position as exhibited in fig. 47 ; and as they become contracted 

 by exosmosis, they drag the primary membrane, which lies 



