1917] Forbes: Irrigation Effects of Coj)per Compounds Upon Crops 415 



whole root system 



6.14 



.00105 



171.00 



In all of the corn samples shown above, the copper content 

 of root systems is very much greater than that in the top por- 

 tions of the plants, amounting to twenty-three times, thirty-four 

 times, and thirteen times as much, respectively. In the aerial 

 parts of all samples copper increases slightly but uniformly to- 

 wards the upper and outer portions of the plants. This must 

 be an effect of transpiration, by which copper in solution is 

 carried to the terminal portions of the plant and there deposited. 

 The fine roots of one sample were found to contain about three 

 times as much copper as the coarse roots — a fact which can be 

 explained by the greater proportion of absorbing surface to 

 weight in small roots. 



With reference to toxic effects, the culture in 0.01 per cent 

 copper carbonate showed only a faint yellow striping of leaves, 

 with no checking of growth. The 0.025 per cent culture gave 

 leaves which were strongly striped with yellow, and the total 

 growth reduced to less than one-half. Toxic effects evident in the 

 top portions of this culture are manifestly to be associated mainly 

 with the greatly increased copper content of its roots, since total 

 amounts of copper in the top portions remain small. The 0.05 

 per cent culture of copper in the form of CusS, or finely powdered 

 chalcocite, showed only faint toxic effects in the tops. The fol- 

 lowing summary indicates the relation between toxic effects and 

 copper content of materials. 



