2 BULLETIN 517, U, S. DEPARTMENT OF AGRICULTURE. 
The fungus was isolated from the rotten tubers and inoculations 
made, as in the previous year. The results were similar to those 
obtained in 1915. Forty isolations of Pythwwm debaryanum were 
made in the 45 attempts. The pathogenicity of the organism was 
demonstrated in many instances by inoculating it into sound tubers 
and reisolating it after the potato had rotted. Inoculations were 
made by inserting small quantities of soil from various potato fields 
into tubers. About 50 per cent of the inoculations produced the 
disease from every sample of soil obtained from land which had been 
reclaimed and farmed for some years and had not been burned over 
recently. 
METHODS OF INVESTIGATION. 
It is considered among the growers that. potatoes would not leak 
if grown on new land (that is, land recently reclaimed) or on burned 
land (that is, land on which the peat soil had caught fire and burned 
more or less deeply). This theory was tested. A number of inocula- 
tions were made from samples of soil from an area that had been 
burned over. In no case was there any infection. Samples of soil 
from two areas of new land, one of which had never been farmed, 
while the other had been planted to potatoes the previous year, were 
tested. Two potatoes out of eight inoculated with soil from the land 
most recently reclaimed rotted, and Rhizopus nigricans was isolated 
from the tubers. All other inoculations gave negative results. 
Potatoes from such lands are not immune when inoculated with 
Pythium debaryanum. The apparent immunity of potatoes grown 
on new land or burned land seems to be due to the absence of the 
organism from the soil or to its presence only in limited areas. 
The general plan of the experiments to demonstrate a method for 
the control of the disease was to sort the potatoes in the field and 
store the injured tubers under conditions as nearly approaching 
those of a commercial warehouse as possible. The sound tubers 
were to be shipped in the usual way. It was planned to examine 
the cars of sound potatoes after they reached the market or after 
they had been shipped and sufficient time had elapsed for the in- 
cubation of the fungus. 
The farm selected for the experiments was one on which a number 
of crops of potatoes had been grown. Several cars of the 1916 crop 
had been shipped and considerable damage from leak had been re- 
ported. In the experiments here described the potatoes were 
harvested and sacked in the field in the usual way. They were then 
hauled to the levee, sorted, resacked, and the sound potatoes shipped. 
The tubers that had been wounded by the removal of branches 
(knobs) and by the digging fork were sorted out, and each lot was 
sacked and stored separately. The wounded tubers remained in a 
well-ventilated warehouse on the levee until sufficient time had 
