1921] 
MATSUMOTO—SPECIALIZATION IN RHIZOCTONIA 55 
growth, etc. Nevertheless, these characteristics alone are not 
considered of specific importance on account of indications given 
later. P1 and B1 were reisolated from affected pods of navy 
beans used for an inoculation experiment (see inoculation ex- 
periment No. 7). Morphological and physiological character- 
istics of these two reisolated strains may be compared as follows: 
REISOLATED STRAIN P1 
(1) Selerotia: cells 12-19 x22- 
6 y. 
(2) Hyphae: diameter 8-14 y, 
turning dark brown when old. 
(3) Invertase activity: (similar 
to reisolated B1). 
(4) Temperature requirement: 
optimum temperature is about 
the same as that of the original 
strain P1. 
REISOLATED STRAIN B1 
(1) Selerotia: cells 14-21 x20- 
0 
u. 
(2) Hyphae: diameter 8-15 p, 
turning dark brown when old. 
(3) Invertase activity: (similar 
to reisolated P1). 
(4) Temperature requirement: 
optimum temperature is some- 
what lower, as compared with 
that of the original strain B1 
(28: C. 
The characteristics and behavior of these two reisolated strains 
are rather similar to those of the original strain P1, although the 
pathogenicity of the reisolated strain B1 is not so pronounced 
as that of P1. The strains compared may be regarded as two 
physiological forms of Rhizoctonia Solani Kühn. 
P7 is strikingly distinguished from the remaining strains by 
its morphological and physiological characters, and is considered 
to be new to science. This strain, however, does not seem to be 
particularly virulent. So far as my present inoculation experi- 
ments are concerned, this strain may be responsible for some 
secondary infections. No definite conclusion may be drawn 
at present concerning the taxonomic relations of B3, owing to 
lack of sufficient data. 
SUMMARY 
1. From the macroscopical and microscopical investigation of 
the 15 different isolations of Rhizoctonia obtained from a wide 
range of hosts of different geographical origin, it was possible at 
the outset to identify some conclusively, so that the number 
was reduced to 6 different types for further physiological studies, 
namely, P1, P4, P7, B1, H, and B3. 
