﻿igo3] CHEMICAL STIMULATIO 97 



toxic than with Elodea, but Co is less so. PtCl^ was not more 

 toxic than could be ascribed to its acidity; gold chlorid was 

 about equally so ; and uranyl (nitrate) was about as toxic as 

 Co. KCN was not tested on tadpoles, but would certainly not 

 have been found harmless as with Elodea. My KCN was strictly 

 p. c, and was about 0,7 as alkaline as equivalent KOH. Their 

 toxicity toward Elodea is about proportional to their alkalinity. 

 The modern work on the toxicity of inorganic salts to higher 

 plants is not as conclusive and satisfactory in its botanical as in 

 its chemical aspects. At least in large part it has been done 

 without reference to the temperature. But I have found, as was 

 a prion reasonable, that at 28° C, and still more at 37. S*" C. (at 

 which the temperature alone is fatal in time), Elodea succumbs 

 much more readily than below 20"" C. If an arbitrary time 

 limit, say 24 hours, is placed on the experiment, it is evident 

 that the higher the temperature the more toxic the substances 

 tested will appear. Beside this, I have some evidence, though 

 not enough to be conclusive, that at higher temperatures the 

 adaptation to the poison does not increase in rapidity in propor- 

 tion to the injurious action; when this is true, the plant may 

 become adapted and thrive in a solution at a lower temperature, 

 which at a higfher w^ould kill it. 



to 



The range of variation in apparently reliable statements as to 

 the toxicity of the same substances with different organisms is 

 nothing short of astounding. Kahlenberg and True place Cu, 

 Fe, Ni, and Co on a par, as to their action on Lnpinus albus. 

 Heald*^ finds Ni and Hg equally toxic to Zea. Coupin^3 says 

 CuSO^ diluted to i (moL?) in 700,000,000 checks the growth 

 of wheat, while AgN03 ^^^^ likewise when i in 1,000,000, and 



^"Heald,F. D., On the toxic effect of dilute solutions of acids and salts upon 

 plants. Box. Gaz. 22:125-153. 1896. 



^^CouPiN, H., Sur la sensibility des v^getaux sup^rieurs a des doses tres faibles 

 des substances toxiques. Comptes Rendus, Paris 132:645-647. 1901. Coupin 

 claims priority for the discovery that distilled water is not in itself a poison, having 

 published it in 1900 (Cf. de Cleves, L'eau distill^e, est-elle pure? in La Nature 

 28 1:196. 1900), and Deherain and Demoussy (Compt. Rend. 132: 523-527- 1901)5 

 having repeated it. The fact was not new by some years when Kahlenberg and I 

 did our work in 1898 (published in 1899). 



■ ■ ^ . 



