302 
Journal of Agricultural Research voi. xxxi. No. 4 
PART I.—THE EFFECT OF STEAM AND CHEMICAL SOIL TREAT¬ 
MENTS ON THE OCCURRENCE OF POTATO WART 
Synchytrium endobioticum has no mycelium, producing only spo¬ 
rangia and swarm spores. The latter infect potato stolons and tubers, 
usually only at the eyes, producing the cauliflower-like outgrowths 
or excrescences commonly called “warts.” These warts soon decay, 
leaving the numerous sporangia to become incorporated in the soil 
and to spread by cultivation, water and air currents, tubers, tools, 
the feet, or .other agents (22). According to apparently authentic re¬ 
ports the sporangia may remain viable in the soil for many years. 
Soil disinfection, if practicable and effective, would immediately re¬ 
move the possible sources of infection. 
Fig. 1—Known distribution of potato wart in the United States in 1921. Field experiments were carried 
out near Freeland, Pa., in the large infected area in eastern Pennsylvania 
The soil disinfection experiments carried out have followed two 
main lines of attack: (1) Tne use of steam by the inverted-pan meth¬ 
od, either alone or in conjunction with a chemical; (2) the use of 
chemicals. 
THE STEAM-PAN TREATMENTS 
Historical 
Gilbert (£) seems to have been the first to try the inverted steam- 
pan method of soil disinfection for controlling a plant disease. In 
testing methods of disinfecting tobacco-seed beds for the control of 
root rot (Thielavia basicola ), Gilbert used the inverted steam-pan on 
three plots, one “ treated for a half hour after the soil had reached a 
temperature of 200° F. as indicated by a soil thermometer inserted 6 to 
8 inches below the surface of the soil, 'a second ? was treated one 
hour at a temperature of 175° ‘and the third ; one and one-half hours 
