396 BOTANICAL GAZETTE [December 



chemical properties in common, and consequently can be grouped 

 together chemically, they cannot be placed in the same biological 

 class. This deduction can be stated in another way, that a plant 

 shows the same discrimination in its reaction to ions as it does in 

 its nutrition requirements. 



Summary 



i. Potassium, sodium, and calcium increase the osmotic value 

 of the leaf cell of Elodea. The same three ions cause no stimulation 

 to streaming after short treatment, and ultimately put a stop to 

 all streaming. 



2. Strontium, barium, and copper decrease the osmotic value of 

 the Elodea leaf cell, owing to exosmosis due to an increase in per- 

 meability. These three ions cause a pronounced stimulation to 

 protoplasmic streaming. 



3. The results obtained by this plasmolytic method of experi- 

 mentation indicate that elements which are of the same chemical 

 class are not therefore necessarily of the same physiological class, 

 as determined by their effect on protoplasm. 



At the time that these experimental data were obtained, I fully 

 appreciated that they were opposed to the widely accepted belief 

 that monovalent cations such as Na produce an effect on permeabil- 

 ity, coagulation, and like phenomena, which is opposite to that 

 caused by bivalent cations such as Ca; and that two bivalent 

 cations such as Ca and Sr each produce the same effect on proto- 

 plasm. The data were there, however, and no other interpretation 

 was possible than that Na and Ca have an effect on protoplasm 

 which is qualitatively the same, although differing quantita- 

 tively, while the effects of Ca and Sr are of opposite kinds. It was 

 impossible to escape the conclusion that there is selective "per- 

 meability" in living cells, and that the valency hypothesis of the 

 diffusion of ions through the protoplasmic "membrane" does not 

 hold strictly. 4 



* After the manuscript of this article had been submitted for publication, an 

 article appeared by Loeb (Jour. Gen. Physiol. 5:231-254. 1922) stating that "NaCl 

 acts similarly to CaCl 2 and LiCl 3 on the rate of diffusion of acid into the egg of 

 Fundulus." As Loeb states, it is thus necessary to regard the earlier experiments as 

 incomplete, and to modify the valency hypothesis as applied to permeability. Certain 



