Ward. — Recent Researches on the Parasitism of Fungi. 15 
than the Barberry, and the uredo-stage of the Peridermium on hosts other 
than Senecio. Here, again, the investigations passed through several stages 
of discovery and of controversy, but the upshot was that in the first place 
morphologically different Fungi growing on grasses were extracted from the 
collective species hitherto named P. graminis — e. g. De Candolle’s ( 38 ) 
Uredo Rubigo-vera, 1815, and Schmidt’s ( 152 ) U. glumarum , 1816, and 
Corda’s ( 50 ) P.coronata, 1837, began to emerge as definitely morphological 
species, especially after De Bary ( 9 ) in 1866 had shown that Aecidium Asperi - 
folii belonged to P. Rubigo-vera and Aecidium Rhamni to P. coronata ; 
and similarly, the various forms of Gy mno sporangium and Roes te Ha were 
sifted out, in connexion with various species of Crataegus, Pyrus , &c. 
Researches along these lines culminated in the demonstration that, quite 
apart from the morphologically distinguishable species of rust, there are 
other forms which, although utterly undistinguishable by the microscope, 
are nevertheless sharply distinct in respect of their parasitism. Eriksson 
especially has proved by careful and long-continued experiments that, for 
instance, the Puccinia graminis which grows on Wheat does not attack 
Rye, Barley, Cocksfoot, Alopecurus , Air a, Agrostis , or Poa, if its uredospores 
are sown on these Grasses. Nevertheless P. graminis is common on these 
hosts. Similarly the uredospores from the P. graminis growing on Rye 
and Barley will not directly infect Wheat or Oats, & c. 
Now, since there are no morphological distinctions between these 
forms of P. graminis on different hosts, while there are physiological or 
biological invisible differences, it is clear they must be distinguished. 
It should be pointed out that De Bary ( 5 ), in 1863, had already insisted 
on the intimate choice of hosts ( choix rigour euP) of the Rust Fungi for 
particular cases ; and had insisted that the morphological differences between 
the aecidium-forms of Chrysomyxa Rhododendri and C. Ledi were so slight 
that these are ‘ rather biological than morphological species.’ 
Schroter, who first called special attention to this matter in 1879 
( 153 , p. 69) in the case of P. Caricis, in 1893 ( 158 , p. 31) proposed to term 
such forms, sister species ( Species sorores). Rostrup ( 144 , p. 40) in 1894 
called them biologiske Arter — i.e. biologic species, using practically the 
same term as Klebahn, who called them biologische Spezies , had proposed 
in 1892 ( 93 , pp. 258 and 332). 
Hitchcock and Carleton in 1894 ( 84 ) proposed the term physiological 
species . 
Eriksson in 1894 ( 60 , p. 292) suggested the term specialisierte Formen 
or formae speciales (specialized forms) and has supported his term with 
much admirable work. 
Rostrup in 1896 ( 145 , p. 37) suggested the term biologic races 
( biologische Rassen ) ; while Magnus in 1894 ( 107 , p. 82) proposed 
Gewohnheitsrassen (adapted races) as the preferable term for such forms. 
