8 . . . tS fct . .- . -4 STUDY- JN CEREAL RUSTS 



Eriksson was making his in Sweden. Their conclusions pointed to 

 the fact that there was not much danger of rust from one cereal infect- 

 ing another. The same phenomenon was observed in rusts on a wide 

 variety of hosts. Magnus (1894 and 1895), Rostrup (1894), Klebahn 

 (1896), Dietel (1899), Ward (1901), Bandi (1903), and others firmly 

 established the fact that this specialization of parasitism was quite 

 common in the various rusts. To the formae speciales of Eriksson 

 various names were applied. Schroeter (see Magnus 1894, p. 360) 

 called them Schwester-Arten, and Rostrup (1894, p. 40) called them 

 biologische Arten, while Hitchcock and Carleton (1894) referred to 

 them as physiological races. 



Neger (1902) found evidences of a similar condition among the 

 Erysiphaceae. Marchal (1902) conducted a large number of cross-inoc- 

 ulations with Erysiphe graminis and concluded that there was a fairly 

 large number of "races specialisees." These did not differ essentially 

 in any morphological character. He showed (1903) and Salmon 

 (1903-2) later, showed that the ascospores behaved in the same way 

 with regard to this specialization of parasitism as did the conidia. 

 Reed (1905) has shown that there may be more than one physiological 

 race upon a single genus of host plant. 



Magnus was one of the first to try to explain the phenomenon of 

 specialization of parasitism. He distinguishes . (1894, p. 366) be- 

 tween "Gewohnheitsrassen" or adaptive races and biologic forms. 

 The former name he applies to such forms as merely show difference 

 in infection power, while those which are fixed he calls biologic forms. 

 Long association with one host plant, he says, may bring the develop- 

 ment from Gewohnheitsrassen to biologic forms. This he showed 

 (1895) to be true not only of rust fungi but of others as well. Dietel 

 (1899) expressed a somewhat similar opinion, his idea being that 

 formerly a given species attacked a variety of hosts, but that it be- 

 came more and more specialized to form first Gewohnheitsrassen and 

 then biologic forms. Eriksson (1902, p. 657) says that rust forms adapt 

 themselves. Where a certain host is present in large numbers, and 

 climatic conditions are favorable, changes take place in favor of the 

 new host. These changes are expressed not only in the vitality of the 

 fungus but also in a higher degree of systematic firmness. The new 

 rust form, he says, becomes separated from its sister forms of parallel 

 origin and becomes "scharf fixiert." His conclusion is, "Das Phanomen 

 der Spezialisierung steht nicht langer da als der Exponent eines dem 

 Schmarotzer innewohnenden, launenhaften und unerklarlichen Triebes, 

 iieue Formen zu produzieren. Dieser Trieb wird durch die umge- 

 benden Verhaltnisse die vegetative Unterlage und das Klima, 

 unter denen der Parasit lebt, in eine bestimmte Richtung geleitet." 

 This, Eriksson (1902, pp. 606 and 654) thinks, accounts for the fact 



