382 ANNALS OF THE MISSOURI BOTANICAL GARDEN 



[Vol. 9 



ment indicates that the foxtail organism is not readily killed by 

 freezing and thawing. 



Effect of sunlight. — Moderately thick sowings of a 48-hour 

 broth culture were made on nutrient agar-poured plates. One- 

 half of each plate was covered with black paper and the plates, 

 resting on ice, were exposed to a bright December sun for 5, 10, 

 15, and 20 minutes, triplicates being used for each time period. 

 They were then incubated at about 32° C. No difference in 

 number of colonies could be detected for any of the periods in the 

 exposed as against the covered half. The results were rathei 

 unexpected since bacterial pathogens are often described as sen- 

 sitive to sunlight, certainly within the range employed, 5 to 15 

 minutes being sufficient to kill or very much retard colony devel- 

 opment in a large number of forms. The experiment was there- 

 fore duplicated in May and exposures of 15, 30, and 45 minutes 

 made to a bright sun. There was hardly more than a 10 per cent 



reduction in the number of colonies on plates exposed 30 and 45 

 minutes as compared to those exposed 15 minutes, the difference 

 being within the limits of experimental error. The number of 

 colonies (about 150) which developed after 45 minutes on the 

 exposed half as compared to the covered half was hardly differ- 

 ent. The organism does not appear to be very sensitive to 

 sunlight. 



Overwintering. — Experiments on the effect of desiccation and 

 freezing indicate that the organism has no difficulty in overwin- 

 tering. Unfortunately diseased material which had been placed 

 out of doors in the fall to be tested the following spring was 

 destroyed so that there is no direct evidence for overwintering. 

 Field observations as well as laboratory studies indicate that 

 overwintering is readily accomplished. The writer has already 

 recorded the presence of the disease for 4 successive seasons on 

 the same field. The organism may be carried over winter either 

 in diseased glumes, or possibly in the soil in diseased leaves. 



Vitality on culture media. — If the substratum is not permitted 

 to dry down, the foxtail organism w 7 ill continue to live for a long 

 time. In liquid media, such as nutrient broth and milk, growth 

 may be obtained after a period of G months, and infections are 

 readily produced from broth cultures kept 4 months at about 25 

 C. However, when the organism growing on nutrient agar slants 

 is kept in the ice-box for 9 months it loses its viability. 



