51 



latter salt for every 16 molecules of Zn(KC3)r, already pre- 

 sent. It therefore requires 5 times as much of the magnes- 

 ium salt to counteract the toxic influence of ^n(NC2)2 in 

 the concentration here used as is required of the calcium 

 salt to produce the same effect. 



The relatively small amounts of the calcixan and 

 magnesium salts which are required to inhibit thj toxic 

 effect of znCNOg)^ in 0.04m concentration preclude any pos- 

 sibility that antagonistic influence of either of the form- 

 er salts might be related to decreased dissociation of the 

 zinc salt brought about by their addition, so that this 

 consideration needs no attention in this case. 



It is interesting to recall here that the effective- 

 ness of I'g(N03)2 in counteracting the toxicity, in the two 

 concentrations studied, of Pb(NC2)2» so as to allow some 

 normal germination of the spores, was also found to be only 

 about one fifth as great as that of Ca(KC3)2. The relative 

 effectiveness of the nitrates of calciim and magnesium is 

 thus seen to be the same whether they are employed to count- 

 eract the toxicity of Pb(NC3)2 or that of Zn(KC3) . 



Zinc nitrate did not seem to stimulate the spores 

 to form appressoria, though hyaline swellings were common 

 in the more concentrated solutions and no direct evidence 

 was obtained as to whether the zinc nitrate enters the 

 spores. 



