1917] Forbes: Irrigation Effects of Copper Compounds Upon Crops 457 



Considering the above observations, we notice that the soils 

 from which samples were taken do not contain injurious amounts 

 of soluble salts. Their nitrogen content, also, is normal. The 

 areas of yellow barley from which samples come are therefore not 

 to be attributed to alkali salts, or to abnormal nitrogen content. 

 Observation in the field, also, failed to indicate that conditions of 

 irrigation, temperature, or light were unfavorable, these condi- 

 tions being the same for both green and yellow samples. 



Excluding these considerations, therefore, we now find that 

 there is uniformly more copper in the roots of yellow barley 

 plants than in those of the green ones, also in the soils in which 

 they occur. The roots of yellow plants, moreover, show the 

 crinkly condition caused (though not exclusively) by copper 

 when present in toxic amounts in the soil. The following state- 

 ment summarizes these observations. 



Lot 1 



The evidence therefore indicates quite conclusively that the 

 two yellow samples owed their color to toxic effects of copper 

 upon the roots of the young plants. Later in the season, how- 

 ever, no difference in mature plants, showing variations in color 

 when young, may be observed. This must be due to the fact 

 that as root systems penetrate more deeply into the soil they 

 escape the surface zone of tailings, with consequent recovery 

 from the effects of copper. 



