Development, and Structure of the Vegetable Cell, 431 



Endosmotic fluids of more potency, saline solutions, acids, 

 sugar, alcohol, &c., which detach the several adherent mem- 

 branes of the superposed cells from one another, have an exos- 

 motic as w^ell as an endosmotic action. 



Hence the membranes of the secondary cells become contracted 

 and separated from the primary cells with which they were pre- 

 viously in immediate contact, by the action of these reagents ; 

 and indeed they detach themselves all round from the external 

 membrane, the separation of these membranes of the two cells 

 not being perfect until the chemical change has commenced but 

 not been completed in one wall. In this case, the membranes 

 continue united where the thickening of the contiguous primary 

 cell-walls has not yet taken place. In the transverse walls or 

 septa this happens, therefore, at the centre, inasmuch as their 

 lignification advances from the periphery, or centripetally. The 

 young joint-cells consequently continue to adhere closely toge- 

 ther, apparently wedged into the central opening of the per- 

 forated discoid septum, as is exhibited in the case of Spirogyra, 

 in Plate VII. fig. 67. 



This phenomenon has especially contributed to support the 

 notion that the adjoining daughter cells constituted originally 

 only one single cell, which has become divided by the thickened 

 portion of the septum. 



In (Edogonium we may convince ourselves, by direct observa- 

 tion, that, notwithstanding these results with reagents, which 

 might serve as arguments for the constriction-theory, there is 

 present a perfect, though it may be an extremely delicate, septum. 



The delusion is still greater if, in this condition (fig. 67), a 

 pressure from one side be exercised on the young septum 

 (whether effected by the one-sided operation of endosmotic fluids 

 or by a change of tension caused by the cutting of a cell in the 

 immediate vicinity of the septum), and chemical reagents be 

 then applied to dissolve the cell-membrane which is undergoing 

 a change in its chemical constitution. 



That many newly formed cell-membranes, or such as are in 

 course of development, are soluble in water, and still more 

 readily in acetic acid, I have already shown in my above-men- 

 tioned memoir on Conferva fontinalis. The cell-membrane, in 

 process of thickening, which occupies the central layer of the 

 septum, is dissolved by ammonia and iodine as well as by 

 acetic acid. 



Of the above-mentioned solvents of the newly thickened cell- 

 membrane, ammonia appears to have the weakest action; its 

 effect, however, is probably the less striking because it acts 

 endosmotically, and not exosmotically, upon the contents of the 

 secondary daughter cells. However, after the operation of am- 



