REED: SPECIALIZATION OF PARASITIC FUNGI 383 
belonging to the various varieties of all the species of Triticum, with 
the exception of certain ones, as those just noted, proved quite sus- 
ceptible when they were tested under greenhouse conditions. Vavilov 
suggests that the greenhouse conditions are much more favorable to 
the development of the powdery mildew and thus more or less immune 
races may be successfully attacked by the fungus. 
The writer (117, 118, 120) has carried on a very extensive series 
of tests with the powdery mildew of the wheat. One hundred and 
sixty-one varieties belonging to the eight recognized types or species 
of Triticum have been tested under greenhouse conditions, many tests 
having been made with nearly all of these. The results are summarized 
in the following table: 
VARIETIES OF SPECIES OR TYPES OF Triticum IN RELATION TO THE WHEAT 
MILDEW 
] 
5 ame Le | 100% infec- o-90% 50-89% | 10-49% -9% 
Species of type Varieties | tion infection | infection | infection | infection 
COMmPpachinn Are = | 2a I 2 | I | 0 
. | 
ID ICOCCUM ms eae 24 8 3 6 g) | 4 
DI OE EOTENS esters Bose ote 45 36 O 6 2 I 
Monococcum......... ye || fo) I 2 I I 
POLGHICUIT A eee TOMN | 9 I oO O fo) 
SyPA TIES £e Oe one ee II 8 I | 2 Ce) (o) 
DUGOUT ee ee a 3 2 2 o. (| (0) 
Vulgare?® . 52,78 35 5 6 3 3 
——— 
hota serrate aeciek ies 161 TOT 5 14 27 10 9 
It is thus seen that the great majority of the varieties are highly 
susceptible to the wheat mildew. It may be specially noted that T. 
dicoccoides Kcke. the wild wheat of Palestine, proved to be quite 
susceptible. The distinctly resistant varieties included T. dicoccum 
var. Khapli, Russian emmer and Spring emmer and T. vulgare var. 
caesium and pyrothrix. 
Various other species of Triticum have also been tested, T. bicorne 
Forsk and T. caudatum Gren. & Godr. proving to be highly susceptible 
and T. triaristatum Gren. & Godr. and T. triuncinale Rasp. proving to 
be resistant. 
The writer (119, 120) has also found that the powdery mildew of 
§Summary includes Triticum Cienfuegos Lagh., T. dicoccoides Kcke., T. Frey- 
cenetitt Host., T. Meyert, T. Tumonia Schrad. and T. durum Desf. var. plenissimum. 
* Summary includes T. abyssinicum Steud. and T. dicoccum Schrank var. campy- 
lodon. 
8 Summary includes T. Thaoudar Reut. and T. dicoccum Schrank var. cladurum. 
9Summary includes T. durum Desf. var. africanum and Triticum species indet. 
var. Tibeian. 
