460 
Journal of Agricultural Research 
Vol. XXI, No. 7 
A recognition of this fact, together with the opportunity offered at the 
Department of Plant Pathology of the University of Wisconsin, led the 
writer to conduct a series of studies upon soil temperature in its various 
relations as affecting the pathogenicity of Corticium vagum upon the 
potato and other hosts. The purpose of this paper is to report part of 
the results of these investigations. 
One of the most important features of the recent development in 
phytopathology, as pointed out by Jones (< 5 ), has been the directing of 
the attention of workers in this field to the vital relation of the tempera¬ 
ture of the soil to a large number of our most serious soil diseases. Our 
present knowledge on this subject is at best limited and fragmentary, and 
the degree to which soil temperature becomes a rigid controlling factor 
in determining pathogenicity is known for but a small number of 
soil pathogens. These data do not permit of extensive generalization. 
It is evident that Corticium vagum , with its wide range of hosts, offers an 
especially favorable object for the study of parasitism in relation to the 
temperature of the soil. 
REVIEW OF LITERATURE 
Observations on soil temperature in relation to the pathogenicity 
of Corticium vagum on its various hosts are few and conflicting. Rolfs 
(rj, 14) concludes that— 
a high temperature and plenty of moisture are necessary for the rapid development 
of the fungus— 
and correlates the high death rate of potato plants in Colorado with 
excessive irrigation during periods of hot weather. 
Peltier (11, p . 283-285 ), in his greenhouse experiments with the car¬ 
nation and other hosts, obtained a higher degree of infection with the 
fungus during the months of June and July and September and October 
than during the cooler months of spring and winter. He supplies other 
minor data to support this relationship and finally concludes his obser¬ 
vations as follows: 
A high temperature, 88 ° F., together with either too little or too much moisture, 
determines to a large degree the virulence of the strains. 
It is evident that this writer has reference here to air temperatures and, 
therefore, adds but little to our knowledge of the exact soil temperatures 
conducive to the pathogenicity of the various strains of the fungus. In 
his later statement we are again left in doubt as to whether he has in 
mind only one or the many hosts with which he worked. 
Morse and Shapovolov (8) noted that in a certain potato field held under 
their observation 50 per cent of the plants showed lesions in the middle 
of July, while on August 4,91 per cent showed evidence of attack by the 
fungus. No temperature data were presented, and it is not clear that 
temperature was an important factor in this relationship, since length of 
