Oct. 30,1916 Spongospora subterranea and Phoma tuberosa 
217 
mained totally free from powdery-scab. This experiment indicates that 
when transplanted outside of the infected section infected soil does not 
yield an infected crop. 
CLIMATIC CONDITIONS THIS CONTROLLING FACTOR IN DISTRIBUTION 
Unless climatic conditions are suitable ,Spongospora subterranea will not 
develop, as is shown in the preceding pages. The studies in Maine 
show that periods of rainfall, followed by cool, damp, cloudy weather 
during the growing season, are periods of infection and are highly es¬ 
sential to the development of the disease. Such periods prevail during 
the growing season not only in the northern sections, but also in Florida, 
where potatoes are planted in January and February and harvested in 
April and May. Moreover, much of the infected area in Florida is in a 
section in which irrigation is practiced, the water there being supplied 
from artesian wells. The water level here is within a few inches of the 
surface for days at a time. Table IV shows the rainfall in the six in¬ 
fected areas during one growing season. 
Table IV. —Average monthly precipitation in powdery-scab-infected areas during the' 
growing season of 1914 or 1915 
State. 
Locality. 
Period. 
Average 
rainfall. 
Florida. 
Washington. 
Hastings (St. Augus¬ 
tine). 
Snohomish. 
February-July, 1915. 
April-October, 1914. 
Inches. 
4. 20 
2. KO 
3 - 64 
4. 70 
2.47 
2. 79 
2. 80 
2 . OO 
Oregon. 
Astoria. 
.do. 
Do. 
Glenora. 
May-October, 1914. 
Minnesota. 
Duluth. 
April—September, 1915. 
Do. 
Virginia. 
.do. 
New York. 
Maine. 
Chateaugay (Danne- 
mora). 
Presque Isle. .. 
April-October, 1914. 
.do. 
Do. 
.do. 
April-October, 1915. 
O' 
2. 08 
Do. 
Van Buren. 
April-October, 1914. 
O 
3 - 46 
3 - 38 
Do. 
.do. 
April-September, 1915. 
prevalence and period of existence of spongospora sub¬ 
terranea IN THIS COUNTRY 
In Aroostook County, Me., Spongospora subterranea exists on many 
farms. In most cases the disease caused by this organism occurs in 
isolated spots, varying from a fraction of an acre to 5 acres; but in 
other places—for example, sections north and northwest of Caribou, 
including Perham, New Sweden, and Stockholm—infection is quite 
general. The disease is always most prevalent on wet, poorly drained 
land. 
During the harvest season of 1914 several fields were examined; and 
notwithstanding the fact that fairly clean seed which had been treated 
with the usual strength of formaldehyde had been used, from 50 to 75 per 
