1922] 



ROSEN — A BACTERIAL DISEASE OF FOXTAIL 



347 



dication on this point and when one considers the difference 

 between night and day temperatures often encountered in the 

 field the data shown are perhaps more indicative of infection to 

 be expected under natural conditions than any experiment would 

 show in which the temperature is kept at one level during the 

 entire incubation period. Roughly then, it may be said that tem- 



90V 



85 



80 



T5 



70 



65 



GO 



»2Hrs 



Fig. 1. Thermographs of artificial inoculations on Winter Turf oats. 



es, during the infection and incubation periods, below 70 

 ent infection, while temperatures above 75° F. are con- 

 to infection. It may be added that numerous artificial 



infection experiments show that heaviest infections occur at 



temperatures between 85 and 95° F. 



ducive 



and 



C 



This 



be expected since growth in artificial culture media is best 



these temperatures, as will be sho 



THE ORGANISM 



Morph 

 sized rod 



The organism 



an 



hether obtained directlv from 



motile, medium 

 le host tissue o 



whether grown on artificial media of various kinds no marked 



differences in morpholoev have been observed 



rather 



der (pi. 27, fig. 2) 

 1.5-2.0 u, 0.6X1.8 



rounded ends, and measures 0.5-0.8 X 



bein 



common measurements 



Very 



rarely is it observed other than singly or in pairs, although occa- 

 sionally a short chain of 4 or G organisms is to be seen. Its motion 

 which is very rapid in warm water, is due to a single, polar flagel- 

 lum which varies somewhat in length but is commonly 3 to £ 



