53 6 BOTANICAL GAZETTE [December 



grow much better when it is present. In his experiments only 

 Na, K, Mg, and Ca were used, and the proportions employed were 

 not those which exist in sea water. 



Summary 



Sodium is as necessary for the marine plants studied as for 

 animals; its replacement in sea water by NH 4 , Ca, Mg, K, Ba, Sr, 

 Cs, Rb, or Li is decidedly injurious. 



The best substitutes for Na are the other kations which pre- 

 dominate in the sea water, Mg, Ca, and K. 



The behavior of various species toward certain salts indicates 

 that each of these salts has a specific action on life processes. 



Laboratory of Plant Physiology 



Harvard University 



