July 8,1918 Can Biologic Forms of Stemrust Change Rapidly? 
117 
host, constant association with this host should increase its virulence. 
The results of trials to determine this are given in diagram 3. 
Diagram 3.— Results of successive transfers of Puurnia graminis tritici-compacti to resistant wheat. 
P. graminis tritici-compacti from Hordeum 
jubatum. 
Hordeum jubatum ^~( s )—W^-; 12 (r) 
W^i i5( r )-W^(r)-W-i(r)• 
CW SS» 
b*J 
^3 
P. graminis tritici-compacti from Elymus 
alaucus. 
36 
R—(r)—R—; 8 
2 7 14 
There was no increase in virulence as a result of keeping the rust on 
wheat, the character of infection being the same at the end of the experi- 
ment as it had been at the beginning. 3 
The effect of hybrids on P. graminis triiici was next tried. The results 
are given in Tables I to V. 
Table) I. Results of inoculations with P. graminis triiici on resistant and susceptible 
parents with rust from susceptible F l hybrid and from stock cultures on susceptible 
parent 
Source of rust. 
Plant inoculated. 
Result. 
j " “ 
i Character of infection. 
Stock cultures.... 
Haynes Bluestem.. 
50 
50 
Heavy; numerous, large uredinia. 
F! hybrid. 
47 
Do. 
Moderate; uredinia smaller, sharp 
flecks. 
Stock cultures.... 
Kubanka 2094. 
47 
49 
49 
Fi hybrid. 
47 
Do. 
1 j 
47 
The F, hybrid plant shown in Plate 13, B, furnished the spore material 
for the inoculations made on the seedling leaves of the parent varieties, 
Haynes Bluestem (Minnesota 169), and Kubanka (Cl 2094). Normal 
a Uredinium too small to transfer. 
b For the character of infection of P. graminis tritici-compacti on Haynes Bluestem wheat (Minnesota 
169) see Stakman and Piemeisel (10, PI. 55, A ), 
