Effect of Copper Compounds 



29 



if it existed. He worked with Pisum sativum, var. arvense, Pisum 

 arvense, Vicia Faba, var. equine Pers, and Fagopyrum esculentum 

 Monch, which were grown in glass distilled water, without any food 

 salts, so that the plants were forced to live on the reserves in the seeds, 

 which were carefully graded to ensure uniformity of size. It was found 

 that in water cultures copper sulphate solutions down to '00000249 / 

 (about 1 in 40,160,000) are harmful to peas, and still further down to 

 0000000249 % (about 1 in 4,016,000,000) the copper salts act as a 

 poison rather than as a stimulant. Against this, however, is the state- 

 ment that in certain soils copper sulphate acts as a stimulant when it 



Fig. 5. Curve showing the mean values of the dry weights of four series of pea plants 

 grown in the presence of copper sulphate and nutrient salts. (Oct. 3rd Dec. 20th, 

 1912.) 



is added in solution. Jensen again could obtain no stimulation with 

 copper sulphate. 



The Rothamsted experiments go to uphold Kanda's statements as 

 to the failure of copper sulphate to stimulate plants grown in water 

 cultures. Peas are perhaps slightly more resistant to the greater 

 strengths of copper sulphate than are barley and buckwheat, for while 

 1/100,000 proves mortal to the latter, peas will struggle on and fruit 

 in 1/50,000, though this strength is very near the limit beyond which no 

 growth can occur (Fig. 4). As a general rule, with barley the depression 

 caused by the poison is still evident with 1/5,000,000 and 1/10,000,000, 

 though occasionally these doses act as indifferent doses, no sign of 



