478 University of California Publications in Agricultural Sciences [Vol. 1 



These ores and the tailings derived from them are rich in 

 potash, and contain unexpectedly large amounts of phosphoric 

 acid ; but nitrogen is almost nil. 



SUMMARY 



1. Copper is shown, as a direct effect of the Clifton-Morenci 

 mining operations in Arizona, to be distributed throughout water- 

 supplies, soils, the vegetable and the animal life of an under- 

 lying irrigated district. 



2. Smaller amounts of copper are found elsewhere in the 

 State where the drainage basin includes mining operations or 

 ore-bearing areas. 



3. Individual plants grown in water cultures or in soil con- 

 taining copper show a comparatively small, and probably not 

 injurious, accumulation of copper in the aerial portions of the 

 plants ; but the root systems, carefully cleansed of externally 

 adhering copper, contain relatively great amounts. 



4. Copper in root systems, as shown by the biuret test, is 

 largely in combination with plant proteids, especially at the 

 growing points of root systems and near vicinity. The place 

 and nature of the reaction accounts for the extreme toxicity of 

 copper salts to plants. The varying sensitiveness of plants to 

 copper salts may possibly be explained in part by the number and 

 disposition of exposed growing points. 



5. Conditions favoring toxicity of copper compounds are the 

 presence of carbon dioxide and certain soluble salts which assist 

 in forming copper solutions that come into contact with plant 



•roots; coarse, sandy soils favoring free access of copper solutions 

 to plant roots and minimizing the withdrawal of copper from 

 solution by adsorption ; and the presence of copper in the form 

 of the more soluble precipitated carbonate. 



