Sept, i, 1921 
Transmission of Some Wilt Diseases in Seed Potatoes 841 
and the other half in the other plot, so that the seed employed was pre¬ 
sumably quite disease-free and was as nearly identical in the two plots 
as possible. In one plot the seed pieces were inoculated by placing on 
top of each a culture of V. ablo-atrum growing on sweet clover stems before 
covering them with soil in the furrow, and the other plot was left uninocu¬ 
lated as a control. The plots were located a short distance apart on the 
same kind of soil on which the crops had been well rotated and which had 
not grown potatoes for at least five years. Ninety-nine per cent of the 
plants on the inoculated plot were affected by V. albo-atrum before the 
end of the season, and none of those on the control plot were found wilted. 
The yield on the diseased plot was 31 per cent less than that on the control 
plot. 
In 1919 two X-acre plots were tested similarly. The seed used came 
from the same lot, but the tubers were not, as in the previous trial, cut 
longitudinally into halves and planted one in each plot. In this test 
there was a 59 per cent lower yield on the diseased than on the healthy 
plot. If the disease attacks the plants early in their growth the yield is 
usually greatly reduced, but if the attack comes late in the season the 
crop is practically normal in amount, though often a high percentage of 
the tubers carry the disease. The average reduction of yield in diseased 
plants probably ranges from 30 to 40 per cent. 
Fusarium oxysporum has been found in 11 counties of Oregon in widely 
separated localities (fig. 6), though much less frequently then Verticillium 
