Effect of Copper Compounds 



21 



other salts remaining the same, the poisonous activity of the copper 

 became greater than could be neutralised by the other salts. If the 

 copper remained the same and the other salts were diminished by half 

 (i.e. below toxic concentration) the neutralising action of the added 

 salts was markedly less, and the growth rate never exceeded that of the 



Tolal. 



Shoot 



*- Root 



40 



25 



42 1 -4 -2 -I 



1 = 1: 100,000 



Pig. 3. Curve showing the dry weights of a series of barley plants grown in the presence 

 of copper sulphate and nutrient salts. (March 13th May 3rd, 1907.) 



NOTE. In each scale of concentrations represented in the curves a convenient inter- 

 mediate strength is selected as a unit, and all other concentrations in the series are 

 expressed in terms of that unit. Thus, with 1/1,000,000 as the unit a scale of concentrations 



might run thus : 



10 1/100,000 



4 1/250,000 



2 1/500,000 



1 1/1,000,000 



0-5 1/2,000,000 



0-1 1/10,000,000 



0-05 1/20,000,000 



O 1 Control. 



