Nov. i, 1915 
Infection Experiments with Timothy Rust 
215 
rye with P. graminis avenae) ; no infection resulted from inoculations on 
timothy. The writers also have two strains of Puccinia graminis, both 
of which have been confined to the same variety of barley for nine months. 
Both attack barley and a number of wild grasses very readily; neither 
has ever infected oats; one attacks wheat with extreme vigor and infects 
rye only with difficulty, while the other is almost entirely unable to infect 
wheat but attacks rye with great vigor. 
It seems fairly clear that, as Johnson (4, p. 10) has previously pointed 
out, timothy rust and Puccinia graminis avenae are quite similar. Both 
rusts transferred to Dactylis glomerata, Avena fatua , A vena elatior , barley, 
rye, Lolium perenne, Lolium italicum , Bromus tectorum , and Elymus spp.; 
the oats rust to Elymus robustus and Elymus canadensis; and the timothy 
rust to Elymus virginicus . With the exception of Avena fatua , they 
transferred with somewhat the same degree of readiness. 
MORPHOLOGY OF THE SPORES 
Morphologically, however, the two rusts are somewhat different, the 
spores of Puccinia graminis avenae being larger. Spores of Puccinia gram- 
mis avenae , originally from Dactylis glomerata and then confined to oats for 
14 successive generations, ranged from 19 to 35/* in length and from 16 
to 24/1 in width, the modes falling at about 30 and 19/*. The spores of 
timothy rust on timothy ranged from 17 to 31/z in length and from 14.5 
to 23 pi in width, the modes falling at about 26 and 18/4. After one gener¬ 
ation on Dactylis glomerata , the timothy-rust spores ranged from 17 to 
32/* in length, and from 13.5 to 23.2 ji in width, while the modes fell at 
about 25.5 and 19.5//. At least 100 spores from different pustules were 
measured. Measurements were also made of spores produced after the 
rust had been one generation on other hosts, including oats, rye, bar¬ 
ley, Lolium perenne , and Avena fatua; but no distinct and consistent 
differences were apparent, with the exception of the spores produced on 
barley. These were smaller than those produced on any other host, 
ranging from 18.5 to 28.3/1 length and from 13 to 2og. in width. The 
modes were at about 23 and 17/*. Whether or not greater variations 
would occur if the rust were confined to the different hosts for longer 
periods of time is not yet known. Experiments have been begun to 
determine the effect of different hosts on the morphology of the spores. 
SUMMARY 
(1) Timothy rust was transferred successfully directly from timothy to 
Avena sativa , Hordeum vulgare, Secale cereale , Avena fatua , Avena elatior , 
Dactylis glomerata , Elymus virginicus , Lolium italicum , Lolium perenne , 
and Bromus tectorum . 
(2) Attempts to increase the infection capabilities of the rust by the 
use of bridging hosts for short periods of time were unsuccessful. 
