1917] Lipman-Gericice : Smelter Wastes and Barley Growth 543 



have noted very definite stimulation of plants by FeS04 in soil 

 cultures. In addition to these direct results on the stimulation 

 of plants, moreover, may be mentioned the numerous cases of 

 stimulation of plants induced by spraying the leaves with solu- 

 tions of FeSO^ either for destroying ever-present weeds in crops 

 or for overcoming certain diseases like chlorosis. These cases 

 are too numerous to mention here, but are well reviewed in the 

 bibliography^ prepared by Horton, which is referred to above. 

 As the discussion of our results has shown, we are in accord with 

 the idea of the stimulating powers of FeS04 even if used in rela- 

 tively large concentrations in soils so far as the first two succes- 

 sive crops on the treated soil are concerned. In the third crop 

 also, marked stimulation is obtained, but only in the higher 

 concentrations, which in the second crop were toxic. This 

 circumstance will be critically considered below. 



Lead Sulfate 



The literature dealing with the subject of the effect of PbSOi 

 or lead in any form on plant growth is very meager. That which 

 is extant deals more specifically with the effect of lead sprays on 

 foliage and fruit of trees than on the actual growth of trees, 

 in which we are interested here. In the case of solution cultures 

 we have found but two papers, and both of these testify to the 

 stimulating action of PbCNOg), in dilute solutions. We refer 

 to the investigations of Jensen^^ and Stoklasa.^*^ In greater con- 

 centration the Pb(N03)o was of course found to be toxic in the 

 solution cultures. The same investigators also obtained marked 

 manifestation of stimulation of plants in solid substrata due to 

 had. Jensen obtained such in quartz-sand cultures, in which 

 greater concentrations were found stimulating than in solution 

 cultures. Stoklasa confirmed the results of the solution cultures 

 by field trials reported in the paper above cited, and also in 

 other experiments"^ with sugar beets, oats, corn, and other crops. 

 A^oelcker"- also found lead to be stimulating to wheat. When 



89Bot. Gaz., 43, p. 11. 



9oCompt. Eend. Acad. Sci. (Paris), 156, p. 153. 



91 Zuckerriibenbau, 18, p. 193 ; E. S. E., 26, p. 225. 



92 Jour. Eoy. Agr. Soc. Eng., 73, ent. series, 1912. 



