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*^:mj.T./t^- 



PLATE I 



Corn root-tips killed in a solution of 1 part copper to 100,000 of water, 

 and colored by means of (1) caustic potash, which gives the violet biuret 

 reaction, identifying both copper and protein; (2) hydrogen sulphide, 

 brown; (3) potassium xanthate, yellow; and (4) potassium ferrocyanide, 

 red. (X ± 30 diam.) 



