446 Wisconsin Academy of Sciences , Arts, and Letters. 
(PL XXXIY, fig. 3), in other cases little or no such harmful 
action occurs. The situation later in the season becomes even 
more puzzling, since the Rhizoetonia may in late summer develop 
as a purely surface growth enveloping the basal part of the 
potato stem with no sign of lesion or canker. This fact has led 
some pathologists to question whether any of these stem cankers 
are due to Rhizoetonia, or whether instead they may not orig¬ 
inate from other causes, with the Rhizoetonia development as a 
purely secondary phenomenon. Our own theory for some time 
past has been that the parasitism of the Rhizoetonia must be in 
some degree dependent upon environmental factors, and early in 
the work with the temperature tanks it was planned to include 
studies upon the possible influence of soil temperature. This un¬ 
dertaking was first projected when R. E. Hartman as a graduate 
student worked upon the organism in 1916-1917. His work was 
interrupted by war service before greenhouse trials along this 
line were inaugurated; but his experience with field plots in 1916 
was significant in that, even where he planted seed potatoes 
abundantly covered with sclerotia, little or no sprout killing or 
stem canker resulted. 
Following this, B. L. Richards as a graduate student and re¬ 
search assistant in this department 2 prosecuted these trials dili¬ 
gently for about two years, presenting the results as his doctor’s 
thesis, which was filed in the University Library, October, 1919. 
This has not as yet been published, 3 but the writer is authorized by 
Dr. Richards to cite here certain of his results. In the first place, 
the evidence secured was fully convincing that the fungus Rhizoe¬ 
tonia (Corticium vagum) is the direct cause of the stem cankering 
of the potato, and, conversely, that adequate seed disinfection gen¬ 
erally serves as a practical preventive for this trouble. The de¬ 
velopment of the stem cankers is, however, dependent not alone 
upon the presence of the fungus but upon favoring environmental 
2 Mr. Richards as plant pathologist at the Utah Experiment Station had 
worked considerably with the Rhizoetonia disease of the potato before coming 
to Wisconsin. In order to enable him to push the work more vigorously 
while here, especially in the field during the summer, he was appointed col¬ 
laborator with Dr. W. A. Orton of the Office of Truck, Cotton, and Forage 
Crop Disease Investigations of the U. S. Department of Agriculture. 
3 This manuscript is entitled “Soil Temperature as a Factor in Determining 
the Pathogenicity of Corticium vagum with Special Reference to the Potato.” 
Dr. Richards has returned to his former relations as plant pathologist of the 
Utah Agricultural Experiment Station, and the publication of his detailed 
results may be expected soon as a bulletin of the Utah Station or in the Journal 
of Agricultural Research. 
