June x8,19x7 
Rhizoctonia solani on Potato 
419 
from the common strain of R . solani. It is therefore impossible to state 
with any degree of accuracy the color of the mycelium and sclerotia on 
the host, the presence or absence of infection cushions, etc. The writers, 
however, are reasonably sure that these characters were not those belong¬ 
ing to R. crocorum. Aside from the above consideration, its similarity 
to R . crocorum is shown by (1) the close agreement of mycelial measure¬ 
ments, (2) the sclerotia in culture approaching the plectenchymatic type. 
The differences are shown by (1) the myceliums lacking the typical 
violet or violet brown pigment in cultures of considerable age on a variety 
of media, (2) the branchings not being at right angles, though occa¬ 
sionally so, and (3) most important perhaps, the ease with which it is 
grown in culture on a variety of media contrary to the experience of all 
former investigators. 
A consideration of the above facts lead the writers to believe that R5 
is to be regarded as a distinct strain of the common R. solani Kuhn as 
occurring on the potato rather than one of R . crocorum (Pers.) DC. 
SUMMARY 
A strain of R . solani Kuhn, for the sake of convenience temporarily 
designated as “R5,” was isolated from potato stems in Maine during the 
summer of 1916. This strain can be distinguished frojn the more com¬ 
mon R . solani by (1) the more pronounced lesions produced when inocu¬ 
lated on injured stems or tubers; (2) the reaction, growth, and character 
of sclerotia on definite media; and (3) morphologically, by measurements 
of the mycelium, of the short sclerotial cells, and, lastly, by the measure¬ 
ment of the diameter of germ tubes when the short, or “barrel-shaped,” 
cells enveloping the sclerotia are placed in drops of water to germinate. 
94352°—17-2 
