518 FROMME: THE CULTURE OF CEREAL RUSTS 
the spores were colorless and failed to germinate. The last 
germination obtained was after 48 days of storage and the spores 
had lost their capacity for germination at some time between 48 
and 80 days. 
Another lot of spores were stored on November 26. These 
germinated in gradually decreasing per cents on January 8, 18, and 
February 2, 11, 18. The length of time required for the develop- 
ment of a germination tube increased from a period of 6-12 hours 
in November to a period of 36-48 hours in February. In the last 
drop culture made, on February 18, only 29 spores of 1,013 tested 
germinated. These few spores, about 0.2 per cent, had germinated 
after 84 days storage. . 
CONTROL OF MILDEW 
The powdery mildew, Erysiphe graminis, became so abundant 
on the oats cultures that measures for its control became necessary. 
The mildew spreads rapidly in the greenhouse and outgrows the 
rust to such an extent that rust culture work may be seriously 
interfered with. Attempts at exclusion of the mildew by isola- 
tion of the cultures and inoculation with uredospores selected 
from apparently non-mildewed leaves proved unavailing. 
The control and total exclusion of the mildew was achieved 
by treatment with sulphur dust. This was applied with a powder 
gun, twenty-four hours after rust inoculation. The plants were 
also atomized with a weak solution of sulphuric acid (1/1000) prior 
to the application of sulphur and were covered afterwards for 
twenty-four hours. With this treatment no mildew adie 
while control cultures became heavily infected. 
This work was undertaken at the suggestion of Prof. R. A. 
Harper, to whom I am indebted for suggestions and criticisms. 
SUMMARY 
1. Two of the cereal rusts, Puccinia dispersa Erikss., on rye, 
and P. coronifera Kleb., on oats, have been cultured in the uredo 
stage, on the living hosts in the greenhouse, for a consecutive 
period of six months, from December 1912 to June 1913, by the 
transfer of infection once a month. P. coronifera was also cultured 
for a period of eight months, from September 1912 to May 1913, 
