510 FROMME: THE CULTURE OF CEREAL RUSTS 
etc. It was found that it was necessary to transfer the infection 
to new cultures once a month. Five ripe, oval pustules were 
selected for each inoculation. The spores from these were removed 
with a scalpel and immersed in 25 c.c. of water in the bottle of the 
atomizer. This was then shaken vigorously to secure uniform 
distribution of the spores before application and the culture was 
subsequently covered with a bell jar for twenty-four hours. 
““Spring’’ rye and “ Kherson”’ oats were used exclusively. About 
twenty-five seeds were sown to a 5-inch pot. 
Six transfers at intervals of a month were made. At first 
seed for the next culture were sown two weeks prior to the date 
set for transfer, but a further simplification of method was secured 
by sowing a month prior to inoculation. Thus sqgwing and transfer 
could be made at the same time. Plants were a month old when 
inoculated and two months old when abandoned. 
Well-infected cultures on both oats and rye were maintained 
for six months in this way. No attempts were made to measure 
exactly the degree of infection secured but the pustules were 
seemingly as numerous at the end of the period as at the beginning. 
Germination tests of spores in drop cultures made at various times 
gave 50-75 per cent. germination in six to twelve hours. The 
_ incubation periods during the six months were quite uniform. 
Twelve days was the longest incubation period recorded and ten 
days the shortest. 
Cultures made in this way show relatively few sori. The 
method provides for maintenance of a rust culture but it does not 
provide an abundant supply of infected plants at all times. 
During the incubation period the pustules have disappeared from 
the old cultures and have not matured on the new ones. To have 
abundantly infected plants continuously available the following 
method was used. Transfers were made once a week instead of 
once a month. Since two weeks were required for complete ripen- 
ing of the pustules it was necessary to run alternate series of host 
cultures. One series was ready for transfer one week and the other 
series the week following. Seeds for subsequent cultures of each 
series were sown at the time of inoculation and the seedlings were 
thus two weeks old when the rust was transferred to them. 
Cultures of P. coronifera have been maintained for eight months 
