THE PERMEABILITY OF CELLS 515 



The combination of a weak base and a weak acid undergoes a 

 greater hydrolytic splitting, more of the free dye base is produced, 

 and the cell should stain more rapidly in the acetate. But such 

 was not found to be the case. 



The addition of a shght amount of acid will prevent the hy- 

 drolytic dissociation and this test must be a surer one than 

 Overton's. I have consequently come to the conclusion that 

 Overton's first hypothesis is the correct one. The detailed evi- 

 dence for this is given below. The dyes used are mostly the same 

 that Overton experimented with belonging to the triphenyl- 

 methane and chinonimid groups. 



b. Elodea: — Pfeffer ('86) first studied the absorption of aniline 

 stains and gave us a clear account of the mechanism of accumu- 

 lation. The dyes collect as granular colored tannin precipitates 

 in Spirogyra. The case of Elodea is different. Neutral red is 

 not typically precipitated, but collects in solution of a red color.^ 

 It likewise collects as a red solution in the vacuole from alkaline 

 tap water of a pale yellow color. This suggested that the sap 

 vacuole is slightly acid and in the acid condition neutral red 

 cannot pass out. Consequently it is slowly accumulated. (Har- 

 vey '10). I was thus led to try staining in weakly acid solution. 

 While it is true that neutral red does not enter from the HCl 

 or CH3COOH acid condition, the acid present in Elodea is prob- 

 ably a very complex organic one. I have been unable to detect 

 any red coloration by crushing the leaves on blue litmus paper. 



The following experiment shows that the dye will not pass into 

 the cell in the acid condition. Elodea leaves were placed in each 

 of the following solutions: 



A. 50 cc. tap water + 1 drop 0.1 per cent neutral red. 



B. 50 cc. 0.001 n HCL + 1 drop 0.1 per cent neutral red. 



C. 50 cc. 0.001 n NaOH + 1 drop 0.1 per cent neutral red. 



After six hours the leaf cells in A and C were found to have 

 accumulated large quantities of the dye while the cells of B con- 

 tain no dye at all. Leaves in B are not injured for protoplasmic 



2 In some cells red globules may be seen; In others red needle crystals. In 

 alkaline condition neutral red is yellow; in neutral and acid condition, red. 



