1917] Lipman-Gericlce : Smelter Wastes and Barley Growth 517 



production, ZnS04 becomes suddenly very much more toxic 

 than at the lower concentrations when more than 2400 p. p. m. 

 is employed in the culture medium here used. At 200 p. p. m. 

 neither the straw and grain on the one hand, nor the roots on 

 the other, are seriously affected in one direction or another by 

 the ZnSO^ in the third crop. Beyond these remarks no dis- 

 cussion of table Vc is necessary. The figures given in that 

 table speak plainly enough for themselves. In contrast with 

 the CUSO4 series of the third crop, however, table Vc shows 

 ZnS04 to be again totally different in its effect on the barley 

 plant in the greenhouse soil. Thus the CuSO^ exercises a stimu- 

 lating effect on total dry-matter production in the third crop at 

 almost all concentrations, while ZnS04, far from doing so in 

 any case, is actually toxic in all concentrations in the third crop 

 on the same soil. This points clearly to sharp differences in 

 the specific physiological effects of the copper and zinc ions, 

 since they were the only apparent variables in question in this 

 experiment. 



Ferrous Sulfate — Greenhouse Soil 



Owing to the rapidity with which ferrous salts are rendered 

 insoluble in well-aerated soils, it was deemed advisable to depart 

 from the procedure followed in the other series so far as quan- 

 tity of FeS04 used is concerned. Applications of the salt were 

 therefore made at intervals of 0.1 per cent between two suc- 

 ceeding cultures in the series, the lowest concentration used in 

 the first crop being 0.1 per cent, and the highest 1 per cent. As 

 in the other series above described on the greenhouse soil (the 

 only one used in the FeS04 series), the amounts of salts were 

 doubled prior to planting the second crop. The results of the 

 yields are given in tables Via, Ylh, and Vic. 



First Crop 



Even though the amounts of FeS04 used were very large, 



we see clearly from table Via that the salt stimulated, in the 



first crop, the production of dry matter in barley. Considering 



averages of duplicate pots, we find that there is no concentration 



