W. J. V. OSTERHOUT 279 



the additional injury due to the toxic action of the salt. For this 

 reason many cells which would recover if very slightly plasmolyzed 

 may not do so if plasmolyzed more strongly, since recovery may 

 require so much time that the process of injury gets the upper hand. 



It was found that recovery was more rapid in NaNOs than in a 

 balanced solution of NaNOs plus Ca(N03)2 or in CaCNOs) or CaCl2 

 alone. Experiments with RbCl and CsCl, with and without the 

 addition of CaCl2, gave similar results. This indicates that in a 

 solution of NaNOs, NaCl, RbCl, or CsCl penetration is more rapid 

 than in Ca(N03)2, CaCl2, or a balanced solution. 



These results agree with those previously obtained by the writer 

 in studying Spirogyra}^ 



The experiments on conductivity were carried out by means of an 

 apparatus consisting of a block of paraffin (P, Fig. 1) in which are 

 two depressions containing platinum electrodes, E, E, covered with 

 platinum black. A connecting groove contains the cells, N, loosely 

 packed together and covered by a glass plate, G. The cells are placed 

 in the groove after it is filled with liquid and great care is taken to 

 avoid air bubles. When a new solution is to be introduced it is 

 poured into T\ it then runs through the groove and escapes by the 

 opening 0; the irrigation is continued until the old solution is com- 

 pletly removed. 



Before beginning the experiments the conductivity of the cell 

 sap was tested^* and found to be equivalent to that of sea water 

 diluted with three parts of tap water (this will be referred to a 0.25 

 sea water). As the cells grew well in 0.20 sea water they were kept 

 in this for some time before each experiment and then transferred to 

 0.25 sea water just before the experiment. The conductivity of 

 the cell sap was then approximately the same as that of the external 

 solution and the fact that the cells had a greater resistance than the 

 solution must be ascribed to the greater resistance of the protoplasm 

 or of the cellulose wall. When the cells were killed by agents which 

 produce no alteration in the cell wall the resifetance fell to approxi- 

 mately that of the solution. It is therefore evident that the in- 

 creased resistance was due to the protoplasm. 



^^ Ostcrhout, VV. J. V., Science, 1911, x.\xiv, 187. 



'^ For this purpose a capillary tube was filled with sap and a platinum elec- 

 trode was inserted into each end of the tube, care being taken to avoid air bubbles. 



