1921] 
MATSUMOTO—SPECIALIZATION IN RHIZOCTONIA 5 
regard to the rusts and powdery mildews. A brief review of the 
important studies will not be superfluous in this connection. 
Magnus might be considered one of the early investigators 
in thisline. He suggested that a particular biologic form might, 
by constant association with one host, change its physiological 
capabilities to such an extent as to develop a new race. Eriksson 
(94), in his eross-inoculation experiments with Puccinia graminis, 
observed the evidence of biologie specialization and noticed that 
the form upon one host species was not always indentical with the 
form upon another. Dietel (99) also noticed that a rust fungus 
which had been capable of attacking a number of plants acquired 
by long association with one species of host somewhat weakened 
capabilities of attacking other forms. Ward (02), in his study 
on the relations between host and parasite in the bromes and 
their brown rust, suggested that each specialized form of Puccinia 
might during the lapse of time actually become a distinct species. 
Eriksson (702) further stated, in a subsequent paper, that the 
trend of specialization might be different in isolated localities. 
Furthermore, Ward (03), in his excellent work concerning the 
occurrence of a “‘bridging species," indicated that some forms of 
bromes might act as "bridging species" in enabling the rust to 
pass indirectly from one group of bromes to another, although 
direct transfer was impossible. 
Salmon (704) also observed a similar phenomenon in Erysiphe 
graminis. 'The same author in his later work showed that the 
virulence of Erysiphe graminis might be changed by certain 
cultural conditions. By injuring leaves and subjecting plants 
to heat, etc., the author was able to infect forms which seemed 
normally immune. Reed (’02, '16), in his diverse cross-inocula- 
tion experiments with Erysiphe graminis, noticed some consider- 
able variation in susceptibility among the species and varieties 
of Triticum, Hordeum, Avena, and Secale, and defined the exist- 
ence of biologic specialization. Shear and Wood (713) stated that 
Glomerella cingulata was exceedingly variable in all its charac- 
ters so far as they had been studied, although the cause of this 
variability was not clear. Further, they noticed that no con- 
stant or definite relation had been established between the 
environmental conditions and the most important variations 
observed. They said: “In any ease the evidence accumulated 
