﻿20 



BULLETIN 1146, U. S. DEPARTMENT OF AGRICULTURE. 



Some of the tubers from copper-sprayed and from unsprayed 

 potato plants grown at Arlington Experimental Farm during the 

 season of 1920 were analyzed for copper (Table 8). The average 

 figure for tubers from copper-sprayed plants grown at Arlington 

 was 13.5 and for those from plants receiving no copper, 11 parts of 

 copper per million. Average figures for tubers grown in other 

 localities were 10 parts of copper per million for those from both 

 the Bordeaux-sprayed and unsprayed vines. The writer (11) has 

 shown that tubers contain only traces of copper, while the roots, 

 stems, and leaves of potato plants contain appreciable quantities. 



During the season of 1921 three separate samples of leaves, stems, 

 and roots from four varieties of potatoes were analyzed for copper. 

 At the time of each analysis nine plants were dug and immediately 

 taken to the laboratory, where they were washed in water. The 

 plants were next dipped in 4 per cent hydrochloric acid for 30 

 seconds and then held in water for 5 minutes. This process was 

 repeated three times. The plants were finally placed in a large tub, 

 covered with water, and allowed to remain overnight. The next 

 day all of the plants were thoroughly rinsed in running water and 

 then in distilled water, after which they were dried in the air. The 

 leaves were used for analysis directly. The stems and roots of all 

 the samples were carefully scraped with a knife to remove the outer 

 layers of plant tissue. The scraped samples were then washed in 

 distilled water to remove any possible copper contamination during 

 the scraping process. Five grams of the dried sample were used 

 for copper analysis by the color imetric method. The acid and water 

 treatments apparently removed all the external copper from the 

 plants, as the results for copper in the roots are higher than those 

 for copper in the leaves. 



Table 9. — Copper in leaves, steins, and roots of Bordeaux-sprayed and un- 

 sprayed potato plants, 1921. 



(Parts per million on the dry basis.) 



Date of 

 digging. 



Variety. 



Leaves. 



Sprayed 

 plants. 



Un- 

 sprayed 

 plants. 



Stems 



Sprayed 

 plants. 



Un- 

 sprayed 

 plants. 



Roots. 



Sprayed 

 plants. 



Un- 

 sprayed 

 plants. 



n-o 2 :: 



Do... 



Do... 



Aug. 18.. 



d ;:; 



Do... 



Sept. 13. 



Do'.'.'. 

 Do... 



Early Ohio 



Early Rose 



Irish Cobbler > 



Green Mountain 2 



Early Ohio 



Early Rose 



Irish Cobbler 



Green Mountain 2 



Early Ohio 



Early Rose 



Irish Cobbler 



Green Mountain.. 



C.6 

 13.0 

 11.0 



8.0 

 10.6 



9.6 

 12.0 

 11.4 

 17.3 

 13. 

 11.0 



9.0 



5.0 

 10.0 

 9.0 

 7.4 

 12.0 

 9.6 

 8.0 

 10.6 

 10.0 

 9.0 

 9.0 

 6.8 



3.4 

 6.6 

 9.3 

 4.6 

 9.4 

 6.0 

 7.6 

 7.0 

 14.0 

 5.0 

 8.1 

 6.3 



2.6 

 4.0 

 8.9 

 5.8 

 8.1 

 8.0 



10.2 

 7.0 



11.2 

 8.5 

 6.3 

 4.4 



6.7 

 18.4 

 21.5 

 7.5 

 16. 2 

 8.6 

 8.4 

 10.1 

 26.0 

 19.4 

 8.3 

 9.1 



3.8 

 7.6 



16.9 

 8.0 

 9.9 



10.4 

 8.0 

 8.6 



13.8 

 9.1 

 9.0 

 6.6 



Sprayed with Pickering spray. 



2 Sprayed with barium-water spray. 



The data for the leaves, stems, and roots, given in Table 9, show 

 certain variations, but in the majority of the samples the correspond- 

 ing figures for the copper-sprayed were higher than those for the 

 unsprayed samples. The roots held the most and the stems the least 



