176 BOTANICAL GAZETTE [SEPTEMBER 
86° F. inclusive. No consistent differences as to viability of spores 
from various hosts and with different greenhouse life histories 
were noted. 
Specimens of rusted A. sativa were collected at Saint Paul, 
Minnesota. Attempts were made to germinate spores at different 
temperatures, which resulted in positive germination tests at rela- 
tively low temperatures (about 7°C.), although apparently not 
above 32°C. A temperature nie about 18°C. seemed to be the 
optimum. 
JOHNSON,’ in his germination studies of uredospores of crown 
rust of oats, came to similar conclusions. He gave 7°-8°C. as the 
minimum, 30°C. as the maximum, and 12°-17°C. as the optimum 
for germination. 
TELIOSPORE GERMINATION.—Uredinial material collected from 
January 21 to April 20 on A. sativa and A. sterilis at Saint Paul, 
Minnesota, was used as the original source of inoculum from which 
sixteen different series of seedling oat hosts in the greenhouse were 
infected. Plants of each series produced telia in abundance. 
Negative results were obtained in all attempts to germinate these 
teliospores. Rusted specimens of either A. sativa or A. sterilis 
were collected from May 19 to May 2 of the year following, at 
Baton Rouge, Louisiana, and Olivia, Rochester, and Saint Paul, 
Minnesota. All attempts at germination gave negative results. 
Summary 
1. Aeciospores from herbarium specimens of Rhamnus were not 
viable after a period of 167 days from date of collection. 
2. Urediniospores from herbarium specimens of Avena sativa 
proved to be viable as long as 87 days after date of collection. 
3. Unprotected urediniospores lost their viability within 22 days, 
with a minimum temperature, during this period, of —27°F. and 
a maximum of 42°F. 
4. When afforded protection with a temperature range similar 
to the unprotected, these spores remained viable as long as 44 days. 
5. Exposed to light, viability of urediniospores was lost within 
3 Jonson, E. C., Cardinal temperatures for the germination of uredospores of 
cereal rust. Phytdpath. 2:47, 48. 
