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286 Journal of Agricultural Research voi. xxn.No. s 



amounts of copper than the stems, but not as much as the roots. The 

 leaves contained less copper than the leaves of the plants grown on the 

 Bordeaux or Pickering treated soils. The tubers from the plot treated 

 with copper sulphate solution were as low in copper as those from the 

 other plots. 



The analyses of the various portions of the conti'ol plants showed the 

 presence of copper, but in smaller amounts than in the plants grown on 

 soil treated with the copper sprays. 



The results of the copper absorption experiments indicate that the 

 potato plants, with the exception of those grown in the soil receiving 

 the solution of copper sulphate where the roots were distinctly injured, 

 distributed the largest part of the absorbed copper to the leaves, while 

 the roots and stems contained appreciable amounts of copper. In all 

 normally sprayed potato plants the largest proportion of the copper is 

 said to be found in the leaves. 



The plants grown on the soil treated with a solution of copper sulphate 

 were small and lacking in vigor. The roots had but few hairs, and 

 showed other signs of injury. The large percentage of copper found in 

 the roots, together with the small size of the roots, indicated some inter- 

 ference with the normal metabolism of the vines. The toxic effect of 

 the soluble copper salt was exerted primarily on the roots of the plants. 

 It was apparent that the soluble copper sulphate had injured the potato 

 plants, while the insoluble copper compounds had not. 



The vines from the Bordeaux plot contained a little more copper than 

 the vines from the Pickering plot, indicating that the extra lime of the 

 Bordeaux spray did not aid in preventing the absorption of copper by 



the plants. 



soil, 



The results of the analyses of the first and last samples of soil taken 

 show that no water-soluble copper was found in any of the samples 

 examined. The amount of copper in the first set of samples (Table II, 

 No. 1, 2, 3, and 4) which were taken before any copper had been added 

 to the soils, is practically the same in all cases. The sets of samples 

 taken before and after the final treatment of the plots show the pres- 

 ence of a large amount of copper in the samples receiving the copper 

 treatments. This means that copper in an insoluble form may be pres- 

 ent in the soil in marked amounts without exerting any apparent toxic 

 action on the growth of potato plants. 



But little copper was found in the soil as a result of spraying with 

 copper sprays according to commercial practice. 



On September 5, shortly after the last treatment of the soil, a few hills 

 of potatoes were dug. The weights and number of the tubers, the per- 

 centage of decayed tubers, as well as the notes taken on the size and 

 appearance of the vines are given in Table III. 



