1917] Lipman-GericTce : Smelter Wastes and Barley Growth 515 



concentrations gave the largest increases of dry matter of roots 

 over the controls. All in all, the effect of ZnSO^ in the case of 

 the first crop on the greenhouse soil must be regarded as one 

 definitely stimulating to the production of dry matter in the 

 barley plant. 



Second Crop 

 While in the first crop the CUSO4 and ZnSO^ series are in 

 general similar so far as the effects of the salts on. the barley 

 plants are concerned, they differ markedly in the second crop. 

 To illustrate, it may first be noted in table V& herewith, on the 

 basis of the total dry matter produced, that ZnSO^ beyond con- 

 centrations of 600 p. p. m. is distinctly toxic to barley in the 

 greenhouse soil. With similar concentrations of CuSO^ in the 

 second crop, the latter salt was not only not toxic beyond 600 

 p. p. m., but was actually more stimulating at most of the higher 

 than at the lower concentrations. It would therefore seem that 

 so far as the yields of the total dry matter are concerned, ZuSO^ 

 is either more toxic than CuSO^ or the latter is more readily 

 adsorbed by the greenhouse soil and thus removed from the 

 active solution which bathes the feeding roots. It must, never- 

 theless, be added that while ZnS04 appears to be definitely more 

 toxic to barley than CuSO^ in the greenhouse soil, it cannot be 

 considered very toxic since 0.06 per cent ZnS04 of the dry weight 

 of the soil is not only not toxic, but actually stimulating. We 

 may now consider for a moment the different components of the 

 total dry matter produced in the second crop of the ZnS04 series. 

 So far as the straw alone is concerned, only a concentration of 

 200 p. p. m. ZnSO^ gave stimulating effects. That concentration 

 produced a wqvj marked stimulation, and good agreement is 

 evident in the duplicate pots. Concentrations in excess of 200 

 p. p. m. depress straw production. Such depression, however, 

 is in some instances not very great, and considerable disagree- 

 ment between duplicates here, as in the copper series, renders 

 it difficult to pass final judgment in the matter. In general, 

 there is little difference in the depressing effects on straw pro- 

 duction of concentrations of ZnS04 varying between 600 p. p. m. 

 and 3000 p. p. m. Beyond 3000 p. p. m. a more definite depress- 



