48 



tion of appressoria and other swellings, but a small amount 

 of normal germination was observed in ail cases. Thus, 

 lig(NC3)2 appears to be only about one fifth as effective in 

 reducing the toxicity of the lead salt as is Ca(NC2)2. 



Magnesium nitrate was not employed in concentration 

 sufficiently high to inhibit all lead effects. The nei.rest 

 approach to normal germination was obtained in a combinat- 

 ion solution containing O.C5m MgCNOg)- and 0.00033m 



Pb(NO,)r,, in which, about half of the germination was nor- 

 3 ^ 



raal. 



From the results obtained with the different comb- 

 inations of calcium and magnesium nitrates with Pb(NC2)2, 

 it is evident that the decrease in toxicity of the Pb(N03)2 

 due to the other salt cannot be caused by a depression of 

 the ionization on account of the common anion. For in the 

 combination containing C.0C4rrn ca(N03)2 with 0.00C66m 

 Pb(N02)2> about 90 per cent of the lead salt was calculated 

 to be in the dissociated condition. In the combination con- 

 taining C .02m Ca(NC3)2 or Mg(N03)2 together with a 0.00066m 

 concentration of the lead salt the latter should be about 

 4C per cent, dissociated. The presence of either of these 

 concentrations of dissociated lead salt alone in a culture 

 solution would either prevent germination entirely or cause 

 abnormal growth. That the decrease in toxicity may have 

 been due to the formation of a double salt remains possible; 

 at least no direct evidence to the contrary was obtained. 



With the concentrations of the Pb(N02)2 that 



