Development, and Structure of the Vegetable Cell. 31 



tlie aecondary cell appears indeed to have lost ita delicmte 

 though firm consistence. In such cases the chlorophyll-layer 

 is found to be surrounded by a thick, almost gelatinous, but 

 viscous layer, capable of being drawn out in threads, which it is 

 often difficult to separate by endosmotic agents from the mem- 

 brane of the primary cell. In this layer, which likewise ex- 

 hibits the reaction of celluline, the contracting chlorophyll-sacs 

 leave behind them the impression of their forms as furrow-like 

 depressions (figs. G5 & 66). 



This state of aggregation of the membrane of the secondary 

 cell appeared to nic to prevail especially among plants whose 

 joint-cells were in process of multiplication. 



The Spirogyra dubia (Kiitzing), represented in fig. 62, bad been 

 immersed for some time in carbonic-acid water, wheu the mem- 

 branes of th< lary cells contracted by the action of a watery 

 solution ol\ lit appeared altered, almost corroded, and in 

 many cells ruptured at the ends daring the contraction, by 

 which means the endogenous cells (a) were enabled to escape 

 from them. These cells contained a great abundance of the 

 above-d - ' -^ celluline, which acquires a red colour by treat- 

 ment \v . ^ rinc and iodine, and, in the course of the further 

 growth of the plants in water containing carbonic acid, appefera 

 to be absorbed. 



In those specimens of Spiromra which have grown for a long 

 time in pure water destitute of nitrogenous compounds, the de- 

 licate membrane of the secondary cell is completely contracted 

 with much facility by the action of a ddute solution of chloiide 

 of calcmin, and is seen to contain no endogenous cells exoflpt 

 the chlorophyll-sacs. Moreover no celluline is discoverable^ 

 although the chlorophyll-sac still usually contains the well* 

 known large starch -vesicles. 



The membranes of the several cells are not coloured blue by 

 the reagents above mentioned ; and I observed a cellulose re- 

 action in them, as well as in those of Cladophora, occasionally 

 only, and as the exception, and then without being able to detect 

 the circumstances upon which this condition of the cell-mem- 

 brane i: ' >1. 



It !• .>tinctly, from what has been stated, that the hy- 



pothesis thai the joint-cells of Spirogyra are filled with a tissue 

 of endogenous cells is perfectly well founded; for mere va- 

 cuoles in a mucilaginous material would not at one time enlarge 

 and at another contract by diosmotic agency, nor would they 

 possess special contents, and in these again contain cellular 

 structures. 



With respect to the nature of the two sorts of cells existing 

 within the joint-cells of Spiroggrm, and also with respect V9 



