1917] Lipman-Gericke : Smelter Wastes and Barley Growth 539 



ments** carried out in our laboratory, that copper is markedly 

 effective in increasing the nitrifying activity of soils; we know, 

 from other results which we have obtained, but not yet published, 

 that the minerals of the soil are rendered more easily available 

 through the action of CuSO^ ; we know from the results of 

 Porchet and Chuard that plant cells may be directly stimulated 

 by CuSO^. It is therefore reasonable to explain any stimulating 

 effects of copper in soil cultures as being of a complex nature 

 and the results of better conditions for plant growth either 

 directly or indirectly induced by copper through influences 

 known to be characteristic of it as just explained. 



Zinc Sulfate 



We may now review, in a manner similar to that employed 

 for CUSO4, the results obtained by other investigators as com- 

 pared with our results on the effects of ZnSO^ on plant growth. 

 Data indicating the toxicity of zinc to plants grown in solution 

 cultures have been obtained by Baumann,*^ Jensen,*" Krauch,*^ 

 Storp,*® True and Gies,*° and Brenchley.'^" Most of these toxic 

 effects were obtained with relatively small quantities of zinc 

 salts and usually under conditions antagonistic to their toxic 

 effects owing to the presence of nutrient salts. As opposed to 

 these evidences of the toxicity to plants of zinc, we have at 

 times, in the work of the same investigators, manifestations of 

 the stimulating effects of zinc in solution cultures. For example, 

 Brenchley admits in the monograph cited a slight stimulation 

 of peas by ZnSO^, while showing the latter to be toxic to barley. 

 Jensen, too, whose work is described, while obtaining no stimu- 

 lation for ZnSO^, likewise showed no toxicity thereof in dilute 

 solution, and expressed the opinion that the possibility exists of 



4-1 Lipman and Burgess, The Effects of Copper, Zinc, Lead, and Iron on 

 Ammonification and Nitrification in Soils, Univ. Calif. Publ. Agri. Sei., 

 vol. 1, p. 127. 



45 Landw. Versuelis. Stat., 31, p. 1. 



46 Bot. Gaz., 43, p. 11. 



47 Jour, f iir Landw., 30, p. 271. 



48 Landw. Jahrb., 12, p. 795. 



49 Bull. Torrey Bot. Club, 30, p. 390. 



50 Inorganic plant poisons and stimulants, Cambridge, 1914. 



