12 



ortions of salts used in these investigations were widely 

 different and it is of course possible that the different 

 conclusions arrived at may have been due to this feature. 

 Furthermore, as fungi and higher plants so frequently re- 

 act differently to the same stimulus, it is possible that 

 one of these two explanations might hold for one group of 

 organisms and the other for the other. The present study, 

 in which a fungus was employed, was undertaken partly to 

 throw light on the question just suggested. 



It is the purpose of this research to examine the 

 effects of the nitrates of copper, lead, zinc, nickel, and 

 aluminum upon the germination of fungus spores, the salts 

 of the heavy metals being used both alone and in combinat- 

 ion with the nitrates of calcium and magnesium, to see 

 whether the presence of the lighter metals in various con- 

 centrations may or may not decrease the toxic effect of 

 the heavy ones. It was also considered worth while, in 

 case such decrease was found to occur, to determine as far 

 as possible whether this influence might be related to the 

 direct effect of salts on each other in the solution or was 

 due to a modification of the organism itself. Furthermore 

 the results obtained in these experiments should throw some 

 light on the problem of the comparative toxicity of the 

 various substances here employed when usei alone, and thus 

 on the general physiological problem of toxicity. 



