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 (71) 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 80 
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 colorimetric 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, stems, and roots of Bordeaux-sprayed and un- 
sprayed potato plants, 1921. 
(Parts per million on the dry basis.) 
Leaves. Stems | Roots. 
aieeine ep ue Sprayed | . U2=_ | sprayed | . U™ . | Sprayed | . UE 
: praye@ | sprayed | PPTAY€* | sprayed | PPTAaYe* | sprayed 
plants plants. plants. plants. plants. plants. 
ues stanly: OhiO- 244-2 See hace ee 6.6 5.0 3.4 2.6 6.7 3.8 
OSs wharly ROSC)— a3. sccinc sack es 13.0 10.0 6.6 4.0 18.4 6 
Doss | sais Cobbler’. 222. Sesh ee 11.0 9.0 9.3 8.9 21.5 16.9 
Do.-.| Green Mountain 2..-......-....- 8.0 7.4 4.6 5.8 7.5 8.0 
Auresisenl Barly @hio..-.2)4.65..0.. ee 10.6 12.0 9.4 S41}: 2 wees 9.9 
1D Ose | tbarhystiOSe se .eke oo aes ooo ce 9.6 9.6 6.0 8.0 8.6 10.4 
Do imishiCopplers. saa cc eb ace 12.0 8.0 7.6 10.2 8.4 8.0 
Do...| Green Mountain 2.--............ 11.4 10.6 7.0 7.0 10.1 8.6 
Senta lonmlarlyshOhiOn =. sas2e 8 feces eae 17.3 10.0 14.0 THIS AaHle 26.0 13.8 
OLvN Barly AROSes. = coo se cc coe ce eee 13.0 9.0 5.0 8.5 19.4 9.1 
Done inshiCopblersss- een. Sse ao 11.0 9.0 8.1 6.3 8.3 9.0 
Do...| Green Mountain.-.-.-...-.....- 9.0 6.8 6.3 4.4 9.1 6.6 
1 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 
; 
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