214 REPORT OF THE BOTANICAL DEPARTMENT OF THE 
) 
been shown by Gillette?’ and also by Kilgore*® that arsenites are 
more injurious to foliage when applied in copper sulphate solu- 
tion than when applied in water. 
Heretofore, it has been supposed that bordeaux mixture pre- 
vents the caustic action of arsenites simply by virtue of the lime 
it contains.®° The results of this experiment shows that not only 
the lime but the copper sulphate, also, is a factor in preventing 
injury. It is also shown that a great excess of lime in the bor- 
deaux is unnecessary. Two pints of the arsenite of soda solu- 
tion may be used safely with 50 gallons of bordeaux made by the 
regular 64-50 formula without the addition of extra lime. 
The fact that Series III treated with arsenite of soda in bor- 
deaux mixture vielded at the rate of 34 bushels per acre less than 
Series IV treated with bordeaux mixture alone tends to show 
that the addition of the arsenite was deleterious; but judgment 
on this point should be deferred untill further tests have been 
made. The yields in this experiment are not entirely reliable. 
The potatoes came up somewhat unevenly and some of the plants 
were considerably injured by Colorado potaito beetles. As there 
was at no time any indication of arsenical injury to the foliage 
on Series III it is difficult to understand how the arsenite could 
have affected the yield. 
It is advised that the arsenite of soda be used on potatoes only 
in combination with bordeaux mixture. 
* Gillette, C. P. Iowa Exp. Sta. Bul. 10: 418, 420. 
Kilgore, B. W. N. C. Exp. Sta. Bul. 77b (Technical Bul. 2): 9, 11. 
* Fraser’s statement (The Potato, p. 138) that, “The copper sulphate 
in the bordeaux mixture seems to prevent the caustic action” (of arsenite 
of soda), and Stewart’s article on this subject (Proc. W. N. Y. Hort. Soe. 
50:87) are both based on the experiment described in this bulletin. 
