Fig. 4. Photograph showing the action of copper sulphate on pea plants in the 

 presence of nutrient salts. (Oct. 3rd Dec. 20th, 1912.) 



1. Control. 



2. 1/50,000 copper sulphate. 



3. 1/100,000 



4. 1/250,000 



5. 1/500,000 



6. 1/1,000,000 



7. 1/2,500,000 



8. 1/5,000,000 ,, ,, 



9. 1/10,000,000 



10. 1/20,000,000 ,, 



