8o 



LON A. HAWKINS 



tion was normal. The main points brought out by these experiments are 

 summarized in table II. 



TABLE II 



From the results obtained with the different combinations of calcium 

 and magnesium nitrates with Pb(NO 3 ) 2 , it is evident that the decrease in 

 toxicity of Pb(NO 3 ) 2 , due to the other salt, cannot be caused by a depression 

 of the ionization of the lead salt on account of the common anion. In the 

 combination containing o.oo4m Ca(NO 3 ) 2 and o.ooo66m Pb(NO 3 ) 2 , about 

 90 per cent, of the lead salt was calculated to be in the dissociated condi- 

 tion. In the combination containing o.O2m Ca(NO 3 ) 2 or Mg(NO 3 ) 2 to- 

 gether with a o.ooo66m concentration of the lead salt, the latter should be 

 about 40 per cent, dissociated. The presence of either of these concentra- 

 tions of dissociated lead salt alone in a culture solution would either prevent 

 germination entirely or give only 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 Pb(NO 3 ) 2 that inhibited germination no 

 granular appearance of the protoplasm, such as was found in otherwise 

 physiologically similar solutions of Cu(NO 3 ) 2 , was evident. Yet it is 

 clear that the lead salt either directly or indirectly affects the protoplasm 

 through the spore wall, as is shown by the formation of the dark bodies 

 occupying one half of the spore in many cases. This response was observed, 

 as has been mentioned, in the higher concentrations of the lead salt. A 

 general discussion of the different forms of germination will be taken up 

 below, after the effects of the combinations of calcium and magnesium 

 nitrates with the other salts have been presented. 



