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 Allu-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 
Galanthus 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 serphyllifolia. 
Malachium aquaticum and Cerastium sp. indet., while Cerastiwm 
arvense, Moehringia trinervig 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 Betula. 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: 
1. 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.) Lév., C. Senecionis 
Fr., Melampsora Evonymi-Caprearum Kleb., M. Larici-epitea 
Kleb., M. Ribesii-purpureae Kleb., Melampsorella Caryo- 
phyllacearum Schroet., Melampsoridium betulinum (Tul.) Kleb., 
