394 BOTANICAL GAZETTE [December 



Discussion 



If the cations potassium, sodium, calcium, strontium, barium, 

 and copper are grouped on a basis of their effect upon the osmotic 

 pressure of the cell sap and streaming of protoplasm, then potas- 

 sium, sodium, and calcium fall into one class, and strontium, barium, 

 and copper into another. Treatment of Elodea cells in potassium 

 nitrate, sodium chloride, and calcium chloride results in an increase 

 in osmotic value of the cell, as evidenced by the increase in critical 

 concentration of the plasmolyzing salt. In contrast with the effect 

 of the bivalent cation calcium on protoplasm is that of the bivalent 

 cations strontium, barium, and copper. 3 As a result of treatment 

 in the salts of these three elements, there is a surprisingly great 

 decrease in osmotic value of the cells. Further, the bivalent cation 

 calcium has no effect on protoplasmic streaming after short treat- 

 ment, and puts an end to all streaming after long treatment, while 

 strontium, barium, and copper cause a pronounced stimulation to 

 streaming until death results from the high toxicity of these three 

 elements. 



There is every reason to regard the reduction in osmotic pressure 

 of the cell, from treatment in strontium, as the result of increased 

 permeability. Through a more porous membrane (using membrane 

 in an abstract sense, since it is probable that the permeability of the 

 protoplast as a whole is affected) an exosmosis of dissolved sub- 

 stances would take place which would lower the osmotic value of 

 the cell. There is the possibility, of course, that the toxic substance 

 might enter the cell and break down larger indiffusible molecules 

 into smaller diffusible ones, and thus cause exosmosis without any 

 change in permeability. The writer considered this possibility 

 in the case of the reduction of osmotic pressure by senegin (a 

 saponin), and was able to show by testing the resistance of the cells 

 to alcohol, and on the basis of other observations as well, that 

 decreased osmotic value of the cell in this case meant increased 

 permeability (8). 



The increase in osmotic pressure of the cell due to treatment in 

 potassium, sodium, and calcium cannot so readily be interpreted 

 in terms of permeability. That there has not been an increase in 



3 Copper in oligodynamic water probably exists as the hydroxide Cu(OH) 2 , and 

 is, as such, bivalent. 



