Journal of Agricultural Research 
Vol. XIV, No. a 
114 
The wheat hybrids inoculated with P. graminis tritici included F x and 
F 3 generation plants, with those of resistant and susceptible parents for 
comparison, and in addition F 0 plants of a hybrid which was breeding 
true for the agronomic characters and showing partial resistance to stem 
rust. Seedlings of Bobs, one of the parent varieties of the cross described 
by Pole Evans (3), were also tested. 
The F t plants were of the cross Haynes Bluestem (Minnesota 169; 
susceptible) X Kubanka (Cl 1 2094; resistant). F 3 plants of two dif¬ 
ferent crosses were used: White Spring emmer (Minnesota 1165; very 
resistant) X Marquis (susceptible); and Marquis (susceptible) X 
Kubanka (Cl 2094; resistant). The F s plants were of the cross Haynes 
Bluestem (Minnesota 169; susceptible) X Kubanka (Cl 2094; resistant). 
Inoculation methods with seedlings were the same as those already 
referred to. The F v and F 3 hybrid plants, which served as sources for 
the material used to inoculate seedlings of the parent varieties, were 
inoculated at time of heading, placed in a large metal moist chamber 
for two days, then removed to the greenhouse bench. 
RESULTS 
Attempts were made to change the parasitic capabilities of P. gram- 
inis tritici-compacti , a new biologic form recently described by Stakman 
and Piemeisel (jo), both by the use of what should theoretically be 
bridging hosts and by confining the rust for a period of time to an un¬ 
congenial host. This rust was selected on account of its action within 
the common-wheat group ( Triticum vulgare). Most hard spring wheats, 
such as Haynes Bluestem, Fife (Minnesota 163), and Marquis, as well 
as many winter wheats of the Crimean group, are resistant, while most 
soft wheats, such as Early Baart, Dicklow, and Washington Bluestem, 
are quite susceptible, as are also the club wheats. The rust differs but 
little from P. graminis tritici except in its action on hard wheats of the 
T. vulgare group. 3 A number of grasses, barley, and club wheats are 
equally congenial hosts for both forms. It would seem that if P. gram¬ 
inis tritici-compacti could be induced to transfer normally to resistant 
hard wheats at all, one of the hosts common to both rust forms should 
act as an intermediary or bridge between the susceptible grass or wheat 
and the resistant hard wheat. Barley, which has been shown by Free¬ 
man and Johnson (5, p . iS) to act as a bridge for P. graminis between 
various cereals, was used in the expectation that it might act as a bridg¬ 
ing host in this case also. The results are given in diagram 1. 
EXPLANATION OE DIAGRAMS I TO 3 
In diagrams 1, 2, and 3 wheat is represented by “W,” barley by “B,” club wheat 
by “CW,” oats by “O,” and rye by “R,” Transfers are indicated by dashes; thus 
“W—B” means that the rust was transferred from wheat to barley and to all other 
cereals indicated in the same vertical column. The results of inoculations are given 
1 Cl “Cereal Investigations No. 
* See Stakman and Piemeisel ( 10 , p. 468-470; PL 54, 55). 
