Vol. XIV, No. 2 
116 Journal of Agricultural Research 
Club wheat is also a host for both P. graministritici and P. graminis 
tritici-compacti. Theoretically, therefore, if bridging species really occur, 
this host might be expected to act as one on account of its close taxo¬ 
nomic relationship to the common wheats. When the tritici-compacti 
rust was found on club wheat in the field, therefore, inoculations were 
made on barley and wheat, and finally the rust was confined to club 
wheat for a period of about four months and transferred to wheat peri¬ 
odically. The results are given in diagram 2. 
Diagram 2.—Effect of club wheat on the parasitic capabilities of Puccinia graminis tritici-compacti 
W^; 3 (r) 
CW— 
B—(s—)—B—(s—)— 
2 5 v 39 
W- 5 -; i(r) 
31 V ' 
B—(s—)— 
3 2 ' 
20 
CW^(s) W^(r)-W^; 3 (r) 
34 
W—; 7 (r)— CW—(s)— 
49 
39 
CW^(s)-CW^s)- 
21 
W ii(r)-CWi5(s) 
CW 2 |(S)- 
,81 
CW^(s)—CW 100 per cent(s)—CW—(s)— 
35 
W ?o« 
CW—(s)“ 
3 2 
W- ; 8(r) 
CW—(s) 
33 1 
W“(r) 
Club wheat did not change the rust at all; neither did the combination 
of barley and club wheat. As a matter of fact, one would scarcely expect 
club wheat to change the rust enough to enable it to attack wheat more 
easily, because it is found on club wheat in the field, and if this host 
changed the fungus it would not remain different from P. graminis 
tritici. 
If neither barley nor club wheat enabled P. graminis tritici-compacti 
to parasitize common wheat more successfully, it would seem possible 
that some other species of Triticum or, more likely still, some susceptible 
variety of T. vulgare might bring about the desired result. Representa¬ 
tives of the different species of Triticum were inoculated, but none 
seemed to give particular promise. Some of the soft wheats of the 
T. vulgare group were found to be susceptible and the rust was trans¬ 
ferred from them to hard wheats. The results were monotonously 
similar to those given in diagrams i and 2. 
After all attempts failed with possible bridging hosts, the effect of 
successive transfers to wheat itself was next tried. If a closely related 
variety or species can suddenly and fundamentally change a rust so as to 
enable it to pass to a normally almost immune variety, it seems reason¬ 
able to suppose that, having once established itself on an almost immune 
« Inoculations made a month after material was collected: consequently few spores germinated. 
& Fife (Minnesota 163). 
