A Dry Rot of the Irish Potato Tuber 
11 
of 1909 the Alliance Commercial Club sent the potato growers 
of that region a circular letter warning them against the danger 
of planting infected seed. This warning was based upon the fact 
that during the previous fall some of the largest potato buyers 
had refused to handle these potatoes on account of the serious 
losses during storage due to this dry rot. The department of 
Agricultural Botany thru circular letters addressed to many of 
the buyers and commission men handling potatoes found that 
during certain Avinters their losses from rotting of the tubers had 
been as high as 20 to 60 per cent. 
One of the most serious losses due to dry rot is the fact that 
the disease forces the immediate sale of the potatoes as soon as 
dag. This tends to demoralize the market and places the grower 
at the mercy of the buyers since he is himself afraid to store his 
crop and wait for better prices. Taken all in all this dry rot 
is perhaps the most serious potato trouble our farmers have to 
contend with in the Sand Hill and High Plains regions. 
SYMPTOMS. 
The dry rot here described is a strict tuber rot affecting 
mature tubers only. Neither the stems nor the young tubers are 
ordinarily in the least affected. Natural infection is known to 
occur solely thru wounds produced in the process of digging or 
subsequent handling. In many cases this rot secures a foot- 
hold thru wounds made by scab-producing animals of certain 
sorts and perhaps even thru scab spots due to fungus parasitism, 
tho the latter method is certainly very rare if we may judge 
from the laboratory experiments, The fungus cannot invade the 
tuber either about the "eyes" or thru the normal lenticels. 
The rotting is rather slow and in general within four to six 
weeks from one-third to three-fourths of the tuber is destroyed. 
The epidermis of the rotted portion becomes slightly wrinkled 
and usually has a characteristic bluish color. On account of the 
rapid destruction of the underlying tissues the surface over these 
areas soon becomes distinctly depressed (Plate I). 
The rot may make its appearance at any point on the surface 
of the tuber tho more commonly perhaps at the bud end of the 
tuber. There is no watery degeneration of the tuber unless other 
organisms gain entrance, so that this is in fact a dry rot. 
MORPHOLOGY OF THE CAUSAL ORGANISM. 
Previous to 1910 no comprehensive work on the genus Fusa- 
rium had appeared which could be considered authoritative and 
the genus was in a very chaotic condition. A species was defined 
