8o 
Journal of Agricultural Research 
Vol. V, No. a 
In order to test still further the effect of moisture on the growth of the 
fungus up into shoots, 12 vigorously germinating tubers of the Green 
Mountain variety were planted in only slightly moist, steam-sterilized 
sand. These tubers grew rapidly, and in six days some of the sprouts 
began to break through the surface of the sand. Twelve days later 2 
of the 12 tubers were dead. The remaining 16 were potted in steam- 
sterilized soil and placed in a glasshouse where the soil was well watered 
and the humidity high. Nine days later one shoot of one of the tubers 
was badly discolored near the surface of the soil. The discoloration 
spread up the stem, and after two days the infected area bore conidio- 
phores of P. infestans in considerable abundance. When the tuber was 
dug up, the shoot was found to be diseased throughout its whole length 
below the surface of the soil. Six days later another tuber showed an 
infected shoot like the one just described. The remaining 8 mother tubers 
were dug up two weeks later and found to. be entirely decayed. These 
results tend to show that continuous high moisture content of the soil 
is not necessary for the growth of the mycelium in the tuber up into the 
stems. According to the results obtained in these experiments, the soil 
may be kept comparatively dry until the plants are up. Furthermore, 
under these conditions the tubers do not rot as rapidly, and a larger 
number of shoots are produced by each. 
INFECTED SEED POTATOES THE CAUSE OF AN EPIDEMIC OF PHYTOPHTHORA 
INFESTANS 
The relation between seed potatoes infected with P. infestans and the 
development of epidemics of the disease under field conditions has received 
consideration both in Europe and in America, but no one has yet been 
able to trace and establish beyond doubt the existing relationship. Both 
De Bary (1, 4) and Jensen (14) claim to have done so, but they made 
only limited tests in the open in gardens, where conditions are not always 
comparable to those existing in the field. A large number of field trials 
having been made with only negative results, coupled with the fact that 
the mycelium grew up into the stems under laboratory conditions, led 
the writer to make field trials. For this purpose a section of the country 
was chosen where this disease occurs annually—namely, northern Maine. 
Such a section should afford the environmental conditions suitable for 
the development of all phases of the disease. 
FIELD STUDIES IN 1913 
The land selected for the experiment had not grown a crop of potatoes 
for at least five years and had been in hay for the preceding four years. 
The infected seed planted was selected in the spring from five bins 
(1,200 bushels each) of potatoes, Irish Cobbler and Green Mountain 
varieties, grown in the vicinity of Houlton, Me., and held in storage 
