1917] Lipman-Gericke : Smelter Wastes and Barley Growth 521 



Second Crop 



In the second crop quite different conditions obtain witli 

 respect to the effects of PbSO^. While nearly all of the higher 

 concentrations of the series are still toxic to barley, three of the 

 lower concentrations, including 600 p. p. m., are distinctly stim- 

 ulating to that plant. If it were not for injury to the plants 

 by mice, the concentrations of 200 p. p. m. and 400 p. p. m. 

 PbSO^ would doubtless have shown as much stimulation as the 

 others just mentioned. In other words, taking the total dry 

 matter produced, it seems true beyond cavil that in the second 

 crop on the greenhouse soil, PbSO^ in very considerable con- 

 centrations acts as a stimulant to barley growth. 



With reference to the separate fractions of the total dry 

 matter produced in the second crop of the PbS04 series, we note 

 some interesting facts. In the first place, no grain was pro- 

 duced in the second crop of the lead series. This is very difficult 

 to explain, since the control pots and the treated ones behaved 

 similarly in that regard. In view of our statements in the intro- 

 ductory portion of this paper, we can scarcely believe that the 

 mere location of the plants of this series in a somewhat shaded 

 part of the greenhouse can account for the discrepancy. The 

 root yields were nearly all depressed by the action of PbSO^ in 

 the second crop. The exceptions to this rule were in isolated 

 pots with no duplicates to confirm them. It would therefore 

 seem that PbSO^ is toxic to the root development of the barley 

 plant even in the second crop, in spite of its stimulating effect 

 on the straw yield at certain concentrations. Such effect of 

 PbSO^ is unlike that of any of the other salts, which, at least 

 at a number of concentrations, stimulate root development, par- 

 ticularly so in the case of CuSO^ and ZnS04. 



Third Crop 

 A progressive improvement may be seen in the soil treated 

 with PbSO^ as crop follows crop. Just as the second crop 

 gave very much better results than the first, so the third crop 

 gave very much better results than the second. In the third 

 crop the stimulation to the growth of barley exerted by PbSO^ 

 is, however, the most striking, since it obtains particularly at 



