REED: SPECIALIZATION OF PARASITIC FUNGI 379 



According to Klebahn (84, 87, 91), Melampsora Larici-pentandrae 

 Kleb., with its aecidial stage on Larix decidua and uredo and teleuto 

 stages on Salix fragilis and S. pentandra, is hardly distinguishable 

 from Melampsora Salicis-albae Kleb., with its aecidial stage on species 

 of Allium and its uredo and teleuto stages on Salix alba, except on the 

 basis of host relations. 



Melampsora Allii-fragilis Kleb. and M. Galanthi-fragilis Kleb. 

 According to Klebahn (84, 85, 87, 91), a similar relation exists between 

 Melampsora Allii-fragilis Kleb., with its aecidial stage on species of 

 Allium and uredo and teleuto stages on Salix fragilis and S. pentandra, 

 and Melampsora Galanthi-fragilis Kleb., with its aecidial stage on 

 Galanthiis nivalis and uredo and teleuto stages on the same two species 

 of Salix. 



Melampsorella Caryophyllacearum (DC.) Schroet. Bubak (24), 

 Klebahn (87), and Fischer (45) have given some evidence for special- 

 ization in this rust. Fischer, using the same collection of aecidio- 

 spores, infected Stellaria media, S. graminea, Arenaria serphyllifoUa. 

 Malachium aquaticum and Cerastium sp. indet., while Cerastium 

 arvense, Moehringia trinervia and M. mucosa were not infected. Kle- 

 bahn obtained somewhat similar results. 



Melampsoridium betulinum (Tul.) Kleb. Klebahn (87, 91) sug- 

 gests the occurrence of at least two specialized races of this rust which 

 has its aecidial stage on Larix decidua and its uredo and teleuto stages 

 on species of Bettila. He found that aecidiospores from Larix, pro- 

 duced by inoculation with teleutospores from Betula pubescens, in- 

 fected B. pubescens and B. nana very abundantly and B. verrucosa 

 sparingly; aecidiospores from Larix, produced by inoculation with 

 teleutospores from Betula verrucosa, infected B. verrucosa abundantly, 

 B. nana sparingly, and B. pubescens not at all. Accordingly the fol- 

 lowing races are indicated : 



1. Betulae-verrucosae Kleb. on Betula verrucosa and B. nana. 



2. Betulae-pubescentis Kleb. on Betula pubescens, B. nana and, to a 



slight extent, on B. verrucosa. 

 The above review lists the occurrence of host specialization in 



more than fifty different rusts. The nature of the specialization of 



these rusts may be indicated by arranging them in the following 



groups : 



I. Heteroecious rusts in which the aecidial host (or hosts) is common 

 to several specialized races which occur on the uredo and teleuto 

 hosts: Coleosporium Campanulae (Pers.) Lev., C. Senecionis 

 Fr., Melampsora Evonymi-Caprearum Kleb., M. Larici-epitea 

 Kleb., M. Ribesii-purpureae Kleb., Melampsorella Caryo- 

 phyllacearum Schroet., Melampsoridium betulinum (Tul.) Kleb., 



