Le Renard^ studied the comparative toxicity of salts 



8 Le Renard, Alf., Influence du milieu sur le resistance du 

 Pencille Crustace aux substances toxiques. Ann. de Sci. Nat. 

 Bot. 16: 276-336. 1912. 



of many of the heavy metals upon Pencillura, the fungus being 

 grown with various concentrations of nutrient media. He 

 used the acetates of potassium, magnesium and ammonium alone, 

 and the acetates, formates, nitrates, phosphates, and sulph- 

 ates of these three metals with glucose. In combination with 

 various concentrations of the salts in the nutrient media 

 he used several concentrations of the chlorides and nitrates 

 of zinc, nickel, cobalt, copper, mercuric chloride, silver 

 nitrate, and the sulphate and acetate of copper. The presence 

 in the nutrient media of the lighter metals in higher con- 

 centration was usually found to decrease the toxicity of the 

 heavy metals. 



True and Gies^ showed that calcium modified the 



9 True, Rodney H., and Gies, W. J., On the physiological 

 action of some of the heavy metals in mixed solutions. Bull. 

 Torr. Bot. Club, 30:390-402, 1903. 



toxicity of various copper salts, zinc sulphate and mercuric 

 chloride in their effect upon the growth of roots of Lupinus 

 albus. In discussing their results these authors say: "The 

 stimulating action of the calcium seems to have operated 



