504°. FROMME: THE CULTURE OF CEREAL RUSTS 
The length of time during which uredospores of P. graminis 
retain their vitality was found by de Bary (3) to vary between 
one and two months, while the aecidiospores of the same form lost : 
their color and capacity for germination in one month. Marshall 
Ward (38) obtained germination with uredospores of P. dispersa 
after having kept them in a dry state for 61 days. Miss Gibson 
(14) reports a germination of 25 per cent. with uredospores of P. 
Chrysanthemi after storage of 71 days but none a week later. 
One aecidiospore of a sowing of Phragmidium Rosae-alpinae 
germinated after storage of 82 days. Barclay (2) found uredo- 
spores of some forms capable of germination during periods of 
from two to eight months (see TABLE 1) in the Himalayas. 
Bolley (5) obtained a 5 per cent germination with uredospores of 
P. graminis after exposure to air and sunlight during the month of 
August. 
Many observers have shown that various rusts are able to 
winter over in the uredo stage in some regions, but these data do 
not involve the determination of the actual time during which the 
spores are viable. 
Gibson (14) has shown that a large number of uredospores will 
germinate on the leaves of the wrong host and that their germ 
tubes will enter the stomata without, however, producing an 
infection. In these cases the end of the germ tube dries up in 
the substomatal chamber without further development. Because 
inoculation does not always result in infection, Marshall Ward 
(37) would distinguish sharply between these terms which are 
often used interchangeably. The passage of the germ tube into 
the host should be spoken of as inoculation and the subsequent 
development in the tissue of the host as infection. Pole Evans 
(rr) has investigated the entrance of the germ tubes of uredospores 
of P. graminis, P. glumarum, P. simplex, and P. coronifera into 
the stomata of their respective hosts and the establishment of the 
mycelium in the tissue of the host. The uredospores germinate 
within twenty-four hours and the infection is well established by 
the third day. When the germ tube reaches a stoma it forms a 
swelling or appressorium directly over it. A branch from the 
appressorium next enters the stomatal slit and forms a large vesicle 
in the substomatal chamber into which the contents of the appres- 
