Nov. 1. 1915 Injection Experiments with Timothy Rust 2 1 5 



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 fatttci, Avena elatior, barley, 

 rye, Lolium pcrenne, 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- 

 inis avenae, originally from Dactylis glomerata and then confined to oats for 

 14 successive generations, ranged from 19 to 35/z in length and from 16 

 to 24^ 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/« in width, the modes falling at about 26 and i^fi. After one gener- 

 ation on Dactylis glomerata, the timothy-rust spores ranged from 17 to 

 32/z in length, and from 13.5 to 23. 2;^ 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 pcrenne, 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// in length and from 13 to 20/( 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 



(i) Timothy rust was transferred successfully directly from timothy to 

 Avena sativa, Hordeum vulgare. Secede 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. 



