88 , Journal of A gricultural Research voi. vm. No. 3 
5 per cent of diseased plants being considered by the growers as repre¬ 
senting a severe attack. However, losses amounting to io or 15 per cent 
or more are by no means unknown; and the writer saw one case in 1911 
where 50 per cent of the plants had been killed by blackleg or the pota¬ 
toes had failed to germinate. It should be mentioned that in this 
instance the seed tubers apparently had been stored under very adverse 
conditions and were not in a fit condition to plant. The writer has never 
seen anything like what Pethybridge has described (25), where appar¬ 
ently sound seed tubers, even if they came from a diseased crop, pro¬ 
duced a large percentage of diseased plants. As will be shown in a later 
section, it has been found that the selection of sound tubers from a 
diseased crop is an important factor in reducing the amount of blackleg 
in the following crop. 
Much less loss has been observed on high, well-drained soils that were 
well adapted to growing potatoes than on low, wet, undrained soils. 
Likewise greater damage has resulted from blackleg in seasons of excessive 
rainfall than in dry seasons. Much greater losses in Maine apparently 
have been experienced since the advent of the southern seed-growing 
industry. As has already been mentioned, certain of the early varieties 
desired for seed purposes by the growers in the South are more susceptible 
to the disease. Blackleg also appears to be more destructive in the South 
than in Maine. 
The above discussion has been limited largely to the losses resulting 
from the failure of the seed tubers to germinate; or if they do germinate, 
to produce plants which will live to mature a crop. The losses which 
result from tuber decay either in the field or in storage should also be 
considered. 
Nearly all writers who have discussed blackleg have laid special stress 
upon the amount of loss which it occasions through destruction of the 
tubers. Harrison (17) estimates a total loss from rot of from 10 to 75 
per cent of the crop in the Province of Ontario. Taking the lower 
figure and allowing 40 cents per bushel, he states that this would 
amount to $720,000 in that Province alone. 
All of the blackleg-producing organisms described, including those 
isolated and studied in Maine, are capable of causing a rapid and com¬ 
plete decay of the tubers, especially when they are immature, or im¬ 
mediately following harvesting. There is no doubt that they can and 
do cause some decay in storage and may be responsible for a considerable 
amount if storage conditions are unfavorable. The writer is fully aware 
that the same disease may produce radically different results in different 
countries under different climatic conditions. However, if he were to 
base his opinion upon his observations of conditions in the northeastern 
part of the United States and adjacent portions of Canada during the 
last 15 or 20 years, he would say that the losses from tuber decay in the 
field and in storage from this source have been largely overestimated. 
