R. P. Wodehouse 457 



In order to preclude the possibility that sulfate was pres- 

 ent, but in some chemical or physical union which prevented it 

 from reacting with barium chloride, Valonia sap which had been 

 shown to give a negative test with this reagent was boiled with 

 nitric acid of several different concentrations, in order to break 

 up any such possible union, and tested again. In each case, 

 however, the test for sulfate was negative. 



In order to test the matter still further, some of the sap was 

 incinerated in a porcelain crucible. Upon incineration it showed 

 the presence of a great deal of organic material, which left a 

 deposit of carbon, but upon being boiled with HC1 and incinerated 

 again this was removed and the residue was completely soluble 

 in water. The sea water, on the other hand, showed no organic 

 material and proved to be largely insoluble in water after the same 

 treatment. The soluble part, however, gave a copious white 

 precipitate with barium chloride, while the Valonia sap after 

 incineration with HC1 gave just a trace, scarcely enough to be 

 'visible. 



The conclusion from the above experiment is that there is 

 little or no sulfate within the vacuole of the normal Valonia cell. 

 Consequently, since there is an abundance of sulfate in the sur- 

 rounding sea water, the semipermeable protoplasmic membrane 

 must possess a selective permeability which renders it imperme- 

 able to sulfate as long as it is alive. This, however, is lost 

 immediately upon death. 



It is of course possible that sulfate may penetrate the outer 

 plasma membrane into the protoplasm without being able to 

 penetrate the vacuole membrane into the vacuole, but upon this 

 point the experiment throws no light. 



In order to test for permeability to nitrates, some cells were 

 placed in sea water to which enough potassium nitrate had been 

 added to give a good nitron test. After 24 hours the cells were 

 still alive (they remained alive for several days when replaced 

 in sea water) and showed the presence of nitrate within by the 

 nitron test. The same was true of sodium nitrate. But it ap- 

 peared upon examination that the control cells in normal sea 

 water also showed the presence of nitrates by the nitron test. 

 Sea water did not show the presence of nitrate by the nitron test. 

 It is therefore evident that the nitrates within the cell must have 



