REED: SPECIALIZATION OF PARASITIC FUNGI 395 



Hordeum vulgare, and Secale cereale are infected by all six races that 

 they worked with. They insist, however, that these races are all 

 distinct and that bridging hosts are not present. The grasses which 

 harbor more than one race of rust are, of course, important in the 

 spread of these races, even though they do not enable them to increase 

 their usual host range. 



Johnson (69) reports that certain grasses enable the timothy rust 

 to extend its normal range. He found that this rust would not directly 

 infect Hordeum vulgare nor Triticum vulgare. However, when the 

 timothy rust was transferred to Avena saliva, the uredospores produced 

 on this host infected Hordeum vulgare. Further uredospores pro- 

 duced on Fesluca elatior by inoculation from timothy infected both 

 Hordeum vulgare and Triticum vulgare. It was also found that uredo- 

 spores from Dactylis glomerata, produced by inoculation from timothy, 

 infected Triticum vulgare. 



Stakman and Jensen (145), however, find no evidence for bridging 

 hosts in the timothy rust. Neither Avena sativa nor Dactylis glomerata 

 increased the host range. They also report that Hordeum vulgare is a 

 host for the timothy rust. Stakman and Piemeisel have further 

 extended the host range of this rust and emphasized its relation to 

 the race Avenae. 



Arthur (5) suggests that Helianthus annuus may be a bridging 

 host for various races of the sunflower rust, Puccinia Helianthi, special- 

 ized to a narrow range of species of Helianthus. H. annuus seems to 

 be readily infected by means of teleutospores from other sunflower 

 hosts. Arthur (3, 4) and Kellerman (74, 75) report successful infec- 

 tions with teleutospores from H. mollis and H. grosse-serratus; Arthur 

 (5) further reports successful infection with teleutospores from H. 

 laetiflorus and Kellerman (75) with teleutospores from H. tuberosus. 

 The teleutospores from these hosts vary in their ability to infect other 

 Helianthus species and, according to results reported, are not able to 

 infect each other except that, according to Arthur, infection of H. 

 mollis occurred when teleutospores from H. laetiflorus were used. 



Neither Arthur nor Kellerman have reported positive tests with the 

 sunflower rust found in nature on H. annuus or produced on it experi- 

 mentally by using spores from other species. Jacky (65) in Europe 

 reports a few tests with teleutospores from H. annuus; these were 

 able to infect only three out of eight species tested. As yet no one 

 has clearly shown that the rust on H. annuus has a wider range of 

 hosts than the rust on H. mollis, H. grosse-serratus, etc. In fact, the 

 evidence is much stronger that H. annuus is a very susceptible host 

 to the various races of rust occurring on other species of Heliatithus, 

 if such races really exist, than that //. annuus is a bridging host. 



