165 
Formae speciales (Eriksson—55) 
Gewohnheitsrassen (Magnus—80, 81) 
Races specialiées (Marchal) 
Mikrospecies 
Biotypes 
Elementary species (de Vries) 
Pure lines (Johannsen) 
Biological forms 
Biological races 
Fischer (56) adopts the practice of recognizing as distinct all forms 
which differ in their choice of hosts in so far as the hosts belong to dif- 
ferent genera; a procedure that leaves the specific rank and name of the 
parasite subject to vicissitudes arising from subsequent changes in the 
conception of the taxonomy of the host. It is yearly becoming more 
evident that distinctions such as these are common in the fungi within 
what were previously regarded as groups of specific rank. 
Biologic specialization in the rusts was announced in 1894 by Eriks- 
son (55), and has since been abundantly attested by Stakman (109), 
Stakman and Piemeisel (111), Stakman, Piemeisel, and Levine (112), by 
Arthur (3, 4), and by others (57, 68). Abundant evidence that it occurs 
in the powdery mildews is afforded by Neger(85) ,Salmon(98),and Reed (92). 
The first demonstrated cases in the fungi imperfecti were probably 
in Helminthosporium, reported by Ravn (91). It was demonstrated in 
Septoria by Beach (12). Reed (93), summarizing regarding biologic 
specialization, cites papers to show its occurrence in the following genera: 
Synchytrium, Albugo, Peronospora, Taphrina, Claviceps, Dibotryon, 
Rhytisma, and Colletotrichum. 
Evidence that there is differentiation morphologically, slight but 
measurable and constant, has been found among the rusts by Arthur 
(3, 4) who, writing of Uromyces on Spartina, says that “the four races 
of this species exhibit not only physiological specialization but a certain 
amount of morphological differentiation.’’ Similar findings are reported 
by Bisby (17) concerning Puccinia epilobii-tetragoni, by Stakman and 
Fiemeisel (111) regarding Puccinia graminis, and by Arthur (3, 4) regard- 
ing Dicaeoma poculiformis on Phleum. Brierley (26) has demonstrated 
by single-spore cultures the existence of elementary species, morphologic- 
ally distinct, within the species of Botrytis, Penicillium, and Stysanus. 
Gaumann (60) has shown Peronospora parasitica to consist of very numer- 
ous races separable on both biologic and morphologic grounds. Similar 
findings regarding Plasmopara are reported by Wartenweiler (124). Pes- 
