126 DiPFUSIOK AND OSMOTIO PeESSUEE 



argued that it is merely a question of osmotic pressure of 

 the solution, and that the chemical nature of the cuprous 

 sulfate has nothing to do with the response ? A third 

 possibility is to conclude that both these factors, always 

 possessed in common by any solution, are active in bringing 

 about the observed result. Obviously these two observa- 

 tions, that the organism lives in a weak solution of CuSO^ 

 and that it dies in a stronger one, are not sufficient to 

 settle the question. 



There are several different ways in which a plant cell 

 may be affected by a solution into which it is plunged. If 

 the solution be concentrated, it may have two effects : 

 (1) Chemically, the solute may produce a response in the 

 protoplasm by diffusing into it, and reacting with it in some 

 way as yet not understood. Thus, the effect of a solution 

 of HgClj upon plant protoplasm is very different from that 

 of cane sugar. (2) Physically, the solution may affect the 

 cell by plasmolyzing it, or partially plasmolyzing it, or by 

 reducing its active turgor pressure. It has been seen that 

 this effect consists primarily in extracting water from the 

 cell. Secondarily, it results in an increased concentration of 

 the contained solution. This latter may again result in a 

 chemical effect upon the living protoplasm, but of this we 

 know absolutely nothing as yet. If the solution be a weak 

 one, its physical effects will be just the reverse of those just 

 mentioned, while its chemical effects will often be the same, 

 but perhaps less marked. Physically, it will allow more 

 water to diffuse into the cell, and there will result a rise in 

 turgidity. 



In order to answer the question stated above with regard 

 to the nature of the effect produced by different concentra- 

 tions of cuprous sulfate, experiments upon the same organism 

 must be performed with other salts and with non-electrolytes, 

 such as cane sugar, glucose, etc. In making these solutions 



