764 
Journal of Agricultural Research 
Vol. XXIII, No. 9 
found under certain conditions in the greenhouse experiments to reach 
its maximum expression at temperatures as low as 12 0 . 
In the case of the two later plantings the young potato shoots pushed 
through the soil at a daily mean temperature approximating very closely 
the optimum for this early period of growth (24 0 C.) at which tempera¬ 
ture the pathogenicity of the fungus, as previously reported, is definitely 
inhibited. This increased rate of growth of the host, together with the 
lessened parasitic action of the fungus at the higher soil temperatures, 
accounts, in a large measure, for the few growing points injured and for 
the decreased severity of the cortical lesions noted in the later crops. 
The sudden rise in the soil temperature might account in a similar 
way for the absence of injury to the primordia of the secondary shoots 
rw 5 10 15 20 25 30J0NE 4 9 14 19 24 50 
Fig. i.—G raph showing the range of the mean daily soil temperature at a depth of 2 inches for Madison, 
Wis., during the months of May and June, 1919. An average mean of 13.5° C. was maintained from 
April 26 to May 25. Between May 25 and 28 the temperature of the soil increased to a daily mean of 
23.5 0 for the period of May 28 to June 30 (Table II and the discussion, p. 763). 
noted in the later two crops (PI. i, A, B). The primary stems from these 
early plantings, as suggested, grew in cold soil which so greatly retarded 
their rate of growth as to permit girdling and killing of the tender buds. 
Later with the rise in the temperature, the secondary shoots arising from 
these injured primary sprouts were permitted to grow so rapidly through 
the soil as to escape practically uninjured. This is especially significant 
in view of the fact that the fungus undoubtedly was present in the soil 
in greater abundance at this later date. 
EVIDENCE OF THE IMPORTANCE OF SOIL TEMPERATURE FROM SEED 
TREATMENT AND PATHOGENICITY TESTS AT PLAINFIELD, WIS. 
During 1918 field studies were made at Plainfield, Wis., for the purpose 
of determining the relation of Corticvwm vagum to seed-potato treatment 
and to crop development. These studies were repeated at the same 
place under comparable conditions in 1919. 5 Such uniformity of cul¬ 
tural methods and general field technic were employed for the two 
seasons as to control as far as possible under field conditions the various 
factors which might affect the virulence of the fungus. No attempt, 
however, was made to modify either the soil temperature or the soil 
moisture content. 
• The details of these field tests will be published at a later date; only such data as relate definitely to 
the effects of soil temperature upon the pathogenicity of Corticium vagum are included in this paper. 
