1917] Forbes: Irrigation Effects of vopper Compounds Upon Crops 413 



in sheep's liver." Human food, however, is commonly contam- 

 inated with copper compounds, which account for its presence 

 in the human body. 



In brief, the observations detailed above have shown the suc- 

 cessive positions of copper in the original ores of the Clifton- 

 Morenci district; in the tailings wastes from these ores, in sus- 

 pension and in solution in river waters exposed to milling 

 operations ; in soils irrigated with these waters ; in the ground 

 waters beneath these soils ; in vegetation growing upon them ; 

 and even in the animal life of the region. It is of interest to ob- 

 serve, first, the concentration through natural processes of small 

 amounts of copper in the original rocks into the form of rich 

 ores; and, second, the reversal, through human agencies, of this 

 process, and the dilution of copper values till, in vegetation and 

 in animal life, but traces of the metal can be detected. 



DISTRIBUTION OF COPPER IN PLANTS WITH ROOT 

 SYSTEMS EXPOSED TO COPPER COMPOUNDS 



Corn Plants Grown in Soils Containing Copper 

 In order to determine accurately the distribution of copper 

 throughout a typical crop plant, thereby locating if possible the 

 points at which injury may occur from copper compounds in the 

 soil, three lots of corn plants were examined in detail. Two of 

 these were grown (August 3 to November 13, 1907) in pots con- 

 taining thirty-eight pounds of sandy loam soil very thoroughly 

 mixed with 0.01 and 0.025 per cent of copper in the form of 

 freshly precipitated copper carbonate (Cu(OH)2.CuC03), made 

 by mixing equivalent amounts of copper sulphate and sodium 

 carbonate. The third was grown in soil containing 0.05 per cent 

 of copper in the form of finely pulverized chalcocite. 



The samples were harvested with care to prevent contamina- 

 tion with copper dust ; the root portions being washed in copper- 

 free water saturated with carbon dioxide until the washings 

 contained no trace of copper. Determinations of copper, as 



5 Blyth, Poisons, fourth edition, pp. 640-641. 



