60 LON A. HAWKINS 



In a later investigation, on the toxicity of copper in combination with 

 various chemical compounds, the same writer 9 has shown, for spore germ- 

 ination in Oedoccphalum albidum and Rhizopus nigricans that ammonium 

 nitrate, sodium sulphate, potassium sulphate, and potassium chloride all 

 markedly decreased the toxic effects of both copper chloride and copper 

 sulphate. He used relatively high concentrations, in some cases five per 

 cent., of the alkali and ammonium salts. He considers the decreased toxicity 

 just mentioned as probably due to the formation of double salts, as he 

 suggested in the case of mercuric chloride. 



Le Renard 10 studied the comparative toxicities of salts of many of the 

 heavy metals upon Penicillium, the fungus being grown in various concen- 

 trations of nutrient media. He used the acetates of potassium, magnesium 

 and ammonium alone, and the acetates, formates, nitrates, phosphates, and 

 sulphates of these three metals with glucose. Also, in combination with 

 various concentrations of the salts in the nutrient medium he used several 

 concentrations of the chlorides and nitrates of zinc, nickel, cobalt and 

 copper, mercuric chloride, silver nitrate, and the sulphate and acetate of 

 copper. The presence in the nutrient medium of the lighter metals in higher 

 concentration was usually found to decrease the toxicity of the heavy 

 metals. 



True and Gies 11 showed that calcium modified the toxicity of various 

 copper salts, of zinc sulphate and of 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 against the retarding action of the copper, and the result is a 

 marked diminution in the poisonous action of the copper." They thus 

 relate this influence of calcium upon copper to a mutual effect of the two 

 salts on the protoplasm. 



Sziics 12 has recently shown that the toxic effect of copper sulphate on 

 the roots of Cucurbita pepo may be inhibited by aluminum chloride in 

 certain concentrations. In this case he used as index of toxicity the ability 

 of the root to react to a geotropic stimulus after it had been removed from 

 the poisonous solution. He varied the presentation time of the toxic stimu- 

 lus (solution of copper sulphate) both alone and with addition of aluminum 

 chloride, and found, for the shorter time periods, that the presence of 

 aluminum inhibited the poisonous action of copper. However, when such 



9 Clark, J.F., On the toxic properties of some copper compounds with special reference to Bordeaux 

 mixture. Bot. Gaz. 33: 26-48. 1902. 



10 Le Renard, Alf., Influence du milieu sur la resistance du Pdnicille crustace aux substances tox- 

 iques. Ann. Sci. Nat. Bot. IX. 16: 276-336. 1912. 



11 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. 



12 Sziics, Joseph, Experimented Beitra^e zu einer Theorie der antagonistischen lonenwirkungen. 

 Jahrb. wiss. Bot. 52: 85-143. 1912. 



