1921] 
MATSUMOTO—SPECIALIZATION IN RHIZOCTONIA z 
and sclerotial growth of the fungi studied. This medium also 
affords a convenient means of separating the various forms into 
the following major groups: (1) the strains which with growth 
blacken the agar; and (2) the strains which do not blacken agar. 
THE STRAINS WHICH BLACKEN AGAR 
P1, isolated from a badly affected stem of potato received 
from Prof. W. T. Horne, California, 1917. 
P2, a culture obtained from a potato stem collected by me at 
Berkeley, California, 1917. 
P3, origin similar to the preceding. 
L1, a culture of this strain obtained from a very badly infected 
lettuce plant, greenhouse, Missouri Botanical Garden. 
El, a culture obtained from a diseased egg-plant (3 inches 
high), Berkeley, California. 
H, obtained from Dr. S. M. Zeller, by whom it had been iso- 
lated from Habenaria sp. (and kept in an incubator for about 
2 months). 
NO PRONOUNCED, AND AT MOST SLIGHT, BLACKENING OF AGAR 
P4 was isolated from sclerotia found on potato tuber obtained 
on the market, St. Louis, 1918. 
P5, origin similar to the preceding. 
P6, isolated from sclerotia on potato tuber obtained in the 
market, Berkeley, California, 1917. 
B1, isolated from a brown lesion on the stem of white navy 
bean, given by Miss E. H. Smith, California, 1917. "The plant 
was not badly infected, having comparatively healthy roots and 
bearing four pods. 
L2, from stock culture in the laboratory of the Missouri 
Botanical Garden. This strain was isolated by one of the former 
graduate students, but the record of its habitat was not at hand. 
B2, obtained from the brown lesion of a certain variety of 
navy beans collected by Dr. Duggar, 1919. 
AGAR NOT BLACKENED 
P7, isolated by me from a potato stem, Berkeley, California. 
'The plant was not seriously affected, but all parts were consider- 
ably dried when found in the late part of autumn, 1917. The 
