CHAPTER XI 



THE BALANCING FUNCTION OF SALTS; 

 IONS AND ANTAGONISM 



A world . . . exists by the balance of antagonism. 



— Carlyle. 



Toxicity. — From the time of the earliest studies on nutrient 

 solutions, it has been observed that any one of the nutrient salts 

 may be toxic or inhibit growth when employed alone. This toxic 

 effect is not produced by plasmolysis (Chap. XIX), but is due 

 to some injurious action of the salt upon the protoplasm of the 

 plant. Several observers of late years have measured this toxic 

 effect; methods of combating it have been developed: and its 

 cause has been explained by many theories. 



Kahlenberg and True (1896) as well as Coupin have expressed 

 the toxicity of different mineral^ salts in respect to wheat by a 

 number, called the equivalent toxicity, which represents the mini- 

 mum quantity in grams which when dissolved in 100 c. c. of water 

 will cause the death of the plant (Coupin) : 



In some cases the toxicity seems to vary directly with the 

 atomic weight of the metal, but that it does not always follow 

 this simple scheme is shown by the fact that salts of lithium (7) are 

 more toxic than those of sodium (23) and of potassium (39). 

 Often the toxic effect is the additive effect of the two kinds of 

 ions which compose it. The iodides are more toxic than the 

 corresponding bromides, which, in turn, are more toxic than the 

 chlorides, as the following table (after Molliard) indicates: 



