165 



Formae speciales (Eriksson 55) 



Gewohnheitsrassen (Magnus 80, 81) 



Races specialiees (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 morpholcgical differentiation." Similar findirgs 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 poculijormis on Phleum. Brierley (26) has demonstrated 

 by single-spore cultures the existence of elementary species, morphologic- 

 ally distinct, w r ithin 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- 



