282 Journal of Agricultural Research voi. xxii, No. s 



OBJECT OF PRESENT EXPERIMENTS 



The experiments discussed in this paper were undertaken to determine 

 what proportion of the copper present in standard Bordeaux spray, in 

 Pickering's limewater Bordeaux spray, and in a solution of copper sul- 

 phate, of equal copper content, is absorbed by potato plants when the 

 sprays or solution are applied directly to the soil in which the vines are 

 growing. The comparative distribution of the absorbed copper in dif- 

 ferent parts of the potato plants was also studied. 



The copper in the Pickering spray was in an insoluble form, basic cop- 

 per sulphate, with no excess of lime present. The copper of the Bordeaux 

 spray was in an insoluble form, with a large excess of lime present. The 

 copper of the solution of copper sulphate v/as soluble. It was believed 

 that a comparative study of these three sprays, containing copper in equal 

 amounts, would show the extent to which the excess lime of Bordeaux 

 spray is instrumental in preventing the absorption of copper by the roots 

 of the potato plants, as well as the relation of the absorption of copper 

 from a soluble copper compound to that from an insoluble copper com- 

 pound when applied to the soil. 



EXPERIMENTAL WORK 



The tests were conducted on the Aroostook Farm of the Maine Agri- 

 cultural Experiment Sta.tion, at Presque Isle, Me., on Caribou type soil. 

 A single row, 8 feet long, of Norcross strain of the Green Mountain variety 

 of Irish potato plants was used for each of four plots which were treated 

 in the following manner : Plot i , sprayed with standard Bordeaux, 3-3-50 

 formula, containing 0.75 per cent of copper sulphate; plot 2, sprayed 

 with an "A ' formula Pickering limewater Bordeaux spray, containing 

 0.70 per cent of copper sulphate; plot 3, sprayed with a solution con- 

 taining 0.75 per cent of copper sulphate; and plot 4, a control plot, un- 

 sprayed. 



The vines were 20- inches above ground when the first applications 

 were made. At each application i gallon of the spray or solution was 

 applied directly to the ground within 6 inches of the stems of eight potato 

 plants in each plot, each vine thus receiving i pint of the solution to each 

 treatment. An equal amount of water was applied to the roots of eight 

 control plants at the time the other applications were made. Applica- 

 tions were made on July 27, August 8, August 17, August 24, and August 

 30, 1917. 



PREPARATION OF SAMPLES 



Vines and tubers from each of the four plots were taken for analysis 

 at frequent intervals. 



The vines from the various plots were dried in the air, then washed in 

 running water and held for 30 seconds in a 4 per cent solution of hydro- 

 chloric acid, after which they were immediately washed in water and 



