1922] 



ROSEN — A BACTERIAL DISEASE OF FOXTAIL 345 



clearly worked out; third, that certain cereals, like oats, barley, 

 and rye, seem to show greater susceptibility, and conversely, that 

 others, like corn and sorghum, are not as susceptible. The in- 

 fection experiments here reported were done entirely in the 

 greenhouse, and at times factors influencing infection, such as 

 temperature, were difficult to control, so that conditions for in- 

 fection were not uniform. The degree of susceptibility was 

 measured by the number and size of the spots produced. 



Isolation and Inoculation Experiments 



The organism was not difficult to isolate, and when once its 

 identity was established and the peculiar behavior of producing 

 a colorless halo surrounded by a white precipitate on certain 

 culture media was recognized, it was easy to detect it on a poured 

 plate, even in the presence of various other Schizomycetes. Dur- 

 ing the 4 years in which this disease has been studied, the patho- 

 gen has been isolated many times from natural infections and 

 from artificial infections on various hosts, using the ordinary 

 method of surface sterilization with 1-1000 mercuric chloride 

 solutions for about 2 minutes, washing in several changes of 

 sterile water, macerating aseptically either in sterile water or 

 in beef bouillon, diluting variously by successive transfers into 

 sterile water blanks, and finally by making poured plates con- 

 taining small amounts of the dilution culture in nutrient agar. 

 When proper precautions are taken, such as a thorough cleans- 

 ing of hands, of clothing, and of the chamber in which the work 

 is conducted it is common to get a series of plates in which the 

 pathogen only is present. 



Since the organism is very sensitive to alcohol, as will be 

 shown later, attempts at surface sterilization with alcohol-mer- 

 curic chloride solution are apt to yield no colonies, although the 

 writer has been able to obtain isolations in this way by a very 

 rapid transfer of the diseased material from the alcoholic solu- 

 tion to the straight mercuric chloride solution. 



In inoculation experiments the organism was at first smeared 

 on the leaves bv means of a sterilized platinum loop and in all 



applied 



method has the 



advantage of enabling one to locate definitely the point of inocu- 

 lation in relation to the point of infection, but it is rather tedious 

 when any number of inoculations are to be attempted. Either 

 agar or broth cultures (the age of the cultures, within limits, 



