1917] Lipman-Gericlce : Smelter Wastes and Barley Growth 511 



portionately smaller on the adobe than on the greenhouse soil, 

 as are the yields of the barley as to tops. Nevertheless, the aver- 

 age yields of roots also show the stimulating effects of CuSO^, 

 since they are greater in all concentrations than those of the 

 control pots until a concentration of 1000 p. p. m. CuSO^, or 

 0.1 per cent based on the dry weight of the soil, is reached. In 

 excess of that concentration, CuSO^ is toxic to roots and appears 

 to inhibit their development. 



Second Crop 

 Much better agreement among the yields of straw in dupli- 

 cate pots of the second crop on the adobe soil was obtained 

 than in any of the series with CuSO^ above described. In fact, 

 the agreement between the duplicates in nearly all cases was 

 as good as could possibly be hoped for when one allows for 

 the ever-present idiosyncrasies of plant protoplasm. Up to 

 and including concentrations of 400 p. p. m., CUSO4 seemed to 

 depress barley growth except in one concentration, namely, 

 at 300 p. p. m. Such depression is probably not significant, 

 except at the concentration of 100 p. p. m. However that may 

 be, CuSO^ did not stimulate the development of barley at the 

 lower concentrations in the second crop on the adobe soil as 

 it did, with one exception, in the first crop. On the contrary, 

 conditions reversed themselves in the second crop, and the most 

 marked and consistent stimulation occurred in the higher con- 

 centrations of CUSO4, only the very highest concentration — 

 namely, 2000 p. p. m. — showing a more or less definitely toxic 

 effect. Thus, while no growth was obtained in the first crop on 

 the adobe soil containing 1500 p. p. m. of CUSO4, the same soil 

 on the second planting stimulated the growth of barley so that 

 in both pots, taken separately and by averages, the yield was 

 superior to that of the control pots. Irregularities of course 

 crept into this series as into the others, for instance, depressed 

 growth or no stimulation at a concentration of 1200 p. p. m., 

 when stimulated growth is obtained at 100 p. p. m. CUSO4 on 

 the one hand and af 1500 p. p. m. on the other, is a circumstance 

 which is very difficult of explanation. 



