400 University of California Fublications in Agricultural Sciences [Vol. 1 



agencies standing between these poisonous salts and the living 

 plant tend to prevent injury/ Soluble copper compounds, for 

 instance, react with carbonate of lime, commonly abundant in 

 soils of the arid region, to form the solid carbonates of copper. 

 The partly decomposed silicates of these soils also precipitate 

 soluble compounds of copper and mask their toxic character. 

 Organic matter in the soil likewise holds large quantities of 

 copper in comparatively harmless combinations. Through physi- 

 cal attraction or adsorption, soluble copper compounds enter into 

 weak combination with fine soil particles and toxic effects are 

 thereby greatly lessened. In the presence, also, of other soluble 

 salts, such as the various forms of "alkali" commonly found in 

 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 s^Tuptoms 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 liy 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 suificiently 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. :\Iead. Edward E. Free. Dr. W. H. Ross and 



1 See Bibliography, pp. 487-488, references 1, 8, 14, 1.1, 16, 19, 34, .31. 



