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 sativa, the uredospores produced 
on this host infected Hordeum vulgare. Further uredospores pro- 
duced on Festuca 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 Helianthus, 
if such races really exist, than that H. annuus is a bridging host. 
