PHYSIOLOGICAL SPECIALIZATION OF PARASITIC 
FUNGI 
GEORGE M. REED 
University of Missouri 
One of the important developments in plant pathology in recent 
years has been the discovery of races of well-defined morphological 
species of parasitic fungi which are restricted to particular hosts. 
These’ specialized races can be distinguished from each other only 
by their ability to grow on some host plants and not on others. It is 
now well established that species of parasitic fungi, identical in their 
structural features as found on a more or less wide range of plants, 
may consist of numerous races or strains which differ in their capacity 
to infect the various hosts. 
Apparently Schroeter (136), as early as 1879, was the first to call 
attention to this phenomenon in connection with certain rusts on 
Carex. It is, however, to Eriksson (34) that we are indebted for a 
realization of the importance and significance of the host specialization 
of fungous parasites and for the impetus to the numerous investiga- 
tions devoted to this phase of plant pathology. Eriksson’s demon- 
stration of races of Puccinia graminis, P. glumarum, P. dispersa and 
P. coronata, distinguishable from each other only on the basis of the 
hosts that they are able to successfully attack, is the real starting point 
for a general recognition of the phenomenon of host specialization of 
fungous parasites. 
Various terms have been introduced to apply to these races or 
strains which show no anatomical differences, but are distinguishable 
only by their physiological behavior in the choice of hosts. Schroeter 
(138), in 1893, suggested the term sister species (Species sorores). 
Klebahn (76), in 1892, described them as biologische Spezies. Rostrup 
(121, 122), in 1894, suggested the term diologiske Arter, and, in 1896, 
proposed another term biologische Rassen. In 1894 Hitchcock and 
Carleton (63) proposed the term physiological species. Eriksson (34), 
in 1894, introduced the generally used expression Specialisierte Formen 
or formae speciales. Magnus (96), in 1894, employed the term 
Gewohnheitsrassen or adapted races. Marchal (97) applied the term 
races spéciali ées, while Ward (174), Salmon (123) and others have 
used the expression biologic forms or biological forms. 
348 
