THE BALANCING FUNCTION OF SALTS 119 



In the same way the various sulphates have an equivalent toxicity 

 which varies with that of the metal contained : 



From the above tables it will be noticed that, of the compounds 

 used by plants in moderately large amounts, magnesium salts are 

 the most toxic. These figures are supported also by the results of 

 Kearney and Harter (1907), who find that magnesium salts in 

 alkali soils are very toxic to wheat. Corn, on the contrary, is not 

 harmed as much by magnesium as by sodium under these condi- 

 tions. The high toxicity of boron and manganese was mentioned 

 in the preceding chapter. 



Antagonism. — It has been noticed by many workers on this 

 subject that when salts are mixed in proper proportions, the 

 toxic effect of the individual salts is overcome. This phenomenon 

 was early studied by Loeb, who used the eggs of Fundulus (a min- 

 now) for his experimental material. When placed in a solution 

 of sodium chloride of the same concentration as the concentra- 

 tion of this salt in sea water, no development of the eggs occurred; 

 but when a trace of calcium chloride, zinc chloride, or of some 

 other bivalent salt was added, the development was normal. The 

 calcium chloride or zinc chloride by themselves are also toxic. 

 The neutralizing in this manner of the toxic effect of one salt by 

 another, also toxic when used alone, is called antagonism. 



Osterhout has studied this matter especially in plants, using 

 both marine and terrestrial forms. The following are some of 

 his results: 



The plants are thus shown to grow more and live longer in mix- 

 tures of the two salts than in either one by itself, but to produce 



