1917] Lipman-Gericke : Smelter Wastes and Barley Growth 559 



With regard to stimulation in soil cultures, there may be 

 added here something which is not mentioned in the discussion 

 above, namely, that the salts of the heavy metals may act with 

 respect to oxydases as Loew^-*^ has claimed manganese does, 

 augmenting their activity and thus preventing the accumulation 

 of toxic materials in the soil. That such a catalytic effect does 

 exist is, however, very doubtful in the light of present evidence. 

 That other forms of catalytic effects may be exerted by such 

 salts as those employed in our experiments is at least not 

 impossible. 



SUMMARY 



The authors have been carrying on a series of investigations 

 on the effects of CuSO^, ZnSO,, FeSO,, PbSO,, MnSO,, MnCl2, 

 KA1( 804)2.12 H2O, and different forms of arsenic on the growth 

 of barley. The experiments were carried out in paraffined earth- 

 enware pots nine inches in diameter, greenhouse soil made up 

 from clay adobe soil and barnyard manure being used prin- 

 cipally. In the case of CUSO4, two other soils were used in 

 addition to the greenhouse soil, namely, the Oakley blow sand 

 and the Berkeley clay adobe. With the greenhouse soil the 

 experiment continued for three successive crops of barley; with 

 the clay abode soil, for two crops; and with the blow sand for 

 only one crop. The results of these experiments, which are set 

 forth in the tables and discussion above, may be summarized and 

 their significance indicated briefly as follows : 



1. In the greenhouse soil, in the first crop CUSO4 acts as a 

 stimulant throughout from concentrations of 50 p. p. m. to 600 

 p. p. m. inclusive. When the roots are left out of consideration, 

 it acts as a stimulant even to the highest concentration employed, 

 viz., 1500 p. p. m. 



In the second crop CUSO4 acts as a stimulant to both roots 

 and tops up to and including 1800 p. p. m., and is without effect 

 on the roots, while stimulating to tops even at 2800 p. p. m. 

 Grain production is stimulated by CUSO4 in the second crop 

 practically throughout the series. 



126 Flora, 91, p. 264. 



