IO 
BULLETIN 70 . 
amounts respectively of clean and diseased potatoes in this 
sack are shown graphically in Plate I. Fig 1. 
From another lot of potatoes which had been in sacks 
for some time 549 pounds were carefully examined. Fifteen 
per cent were free from disease, so far as could be de¬ 
termined, and 85 per cent were infected. Many of the sprouts 
had been overrun with the hyphae, and sclerotia had been 
developed freely on both sprouts and tubers. (See Plate IV.) 
Some of the sprouts had been completely cut off; the tips 
frequently suffered most severely, and the ends of many 
of the sprouts were dead and dry. (See Plate II. Fig. 2.) 
Fifteen of the diseased tubers were placed in moist 
chambers. Five of them developed sclerotia on tubers and 
sprouts. The fungus on the remaining ten was apparently 
dead, and no further development took place. These po¬ 
tatoes were carefully watched and examined from time to 
time. Apparently the development of the disease ceased 
soon after they had been removed from the sack. Ex¬ 
posure to the dry air and sunlight probably killed the fun¬ 
gus. Experiments and observations indicate that excessive 
drying and sunlight kills the hyphae and sclerotia which 
grow on the surface of potatoes, and that the hyphae which 
grow in the deeper wounds are probably not much influ¬ 
enced by such treatment. 
Potatoes from these lots early in the season gave a 
much lower percentage of infection. In neither case did it 
exceed thirty per cent. In the lots examined during the 
winter before the tubers were placed in sacks, the propor¬ 
tion was usually low, and seldom exceeded twenty per cent. 
It is evident that under favorable conditions infected 
potatoes develop hyphae and sclerotia freely after being 
stored. A few diseased potatoes in a bin or sack of clean 
ones, under suitable conditions will spread the disease, and 
in a short time may render the entire lot worthless for seed. 
The cracked skin and rough surface on so many pota¬ 
toes from diseased fields, led us to suspect that Rhizoctonia 
had more or less influence in bringing about this condition 
and the constant association of this fungus with these in¬ 
juries also pointed strongly toward this conclusion. 
Observations show that the hyphae frequently enter the 
lenticells of the tubers and produce corroded spots, or min¬ 
ute open pustules. In rapidly growing tubers such openings 
are often extended, producing numerous cracks which fre¬ 
quently become confluent. These cracks are repaired by a 
natural effort frequently producing a peculiar corky, or ap- 
oarently a double skin on the potato as shown in Plate I. Fig3. 
