July i, 1921 
Pathogenicity of Corticium vagum on the Potato 
477 
we are concerned with one or a group of organisms possibly widely differ¬ 
ent and capable under the conditions of the experiment of producing 
results similar to those secured with the pure culture of Corticium vagum 
described as strain 201. These questions were kept constantly in mind, 
and special studies were made during the progress of the work. 
It is evident from the uniform freedom of the control plants from dis¬ 
ease that the organism or organisms responsible for the lesions occurring 
in the inoculated soil were introduced by the various methods used and 
were not resident in the soil in which the potato plants were grown. In 
but two experiments did typical lesions occur on any control plants, 
and in each of these as reported the threads of “Rhizoctonia” were 
abundantly and unmistakably present. 
The lesion on the potato stems in the sclerotia-inoculated soil were 
found to be indistinguishable from those produced with the pure cul¬ 
tures of the fungus in sterile soil. With both methods of inoculation the 
fungus was found constantly associated with the resulting cankers. 
When there was doubt the presence of the fungus was determined either 
by the use of the compound miscroscope or by cultural methods. During 
the studies isolations were also made from 138 lesions produced in 
sclerotia-inoculated soil. Seventy-eight per cent of these yielded pure 
cultures of Corticium vagum. From the remaining 22 per cent this 
fungus was obtained so intimately associated with other fungi that 
separation was not attempted. A somewhat higher percentage of pure 
cultures of the fungus was obtained from lesions produced in the arti¬ 
ficially inoculated soil. 
A further study of the casual relation of Corticium vagum to the lesions 
produced in soil inoculated with sclerotia was made by removing all the 
sclerotia from 25 of the potatoes selected from the same seed as was used 
in experiment 5. The tubers were then treated for two hours in the 
standard solution of mercuric chlorid and planted in contact again with 
the scleroti in steam-sterilized soil. The pots were then held at tem¬ 
peratures from 18 0 to 22 0 C. The results were comparable in every 
way with those obtained in the sclerotia-inoculated soil in experiment 5* 
With the partially sterilized tubers in experiment 5 the same type of 
lesions was obtained as with the pure culture of the fungus and with 
untreated tuber-borne sclerotia. Finally, the temperature data in 
general supported the conclusion that in the two methods of inoculation 
the same fungus or closely related strains were responsible for the pro¬ 
duction of the type of lesions concerned. It must be kept in mind, 
however, that with the introduction into the soil of a potato the surface 
of which is covered with a large number of organisms, we are introducing 
complicating factors; and it seems quite probable that some of these 
organisms may be important factors in increasing the severity of resulting 
lesions, or on the other hand, they may possibly inhibit the pathogenic 
