Introduction 149 



the soils of the region, the toxicity of copper compounds is enor- 

 mously lessened. 



The investigations recorded in this publication include: (1) 

 Observations upon the distribution of copper in mining wastes, 

 in irrigating waters, in soils and soil waters, in the plants, and 

 in the animal life of the region. (2) The development of accu- 

 rate methods for the determination of minute amounts of copper 

 in all situations where they may occur. (3) Plant cultural 

 work with waters and in soils in the presence of varying propor- 

 tions of copper and under varying conditions. (4) A careful 

 analytical study of the results of such cultures in order to deter- 

 mine the symptoms of poisoning and the distribution of copper 

 throughout poisoned plants; and to identify, if possible, the 

 particular parts of plants and tissues injured by copper. (5) 

 A physiological study of plant reactions with copper. (6) Field 

 studies for the purpose of relating the results of laboratory inves- 

 tigations to the question of economic injury done by copper salts 

 to irrigated crops. 



By reason of interruptions due to other duties, it has required 

 a long time to mature this investigation to the point where it 

 seems sufficiently complete for publication. This delay, however, 

 has given perspective to the work and, especially, opportunity to 

 verify earlier conclusions as applied to field conditions. 



The writer is indebted for painstaking analytical work to 

 Messrs. R. G. Mead, Edward E. Free, Dr. W. H. Ross and 

 C. N. Catlin, associated with the Arizona Agricultural Experi- 

 ment Station from time to time; and to the helpful advice of 

 Dr. Howard S. Reed, of the University of California Graduate 

 School of Tropical Agriculture, in connection with the physio- 

 logical part of the work herein described. The publication, also, 

 has been criticized to its advantage by Dr. C. B. Lipman of the 

 University of California. 



