144 Journal of Agricultural Research voi.xix. N0.4 



varying from o to 30 per cent. Counts of 40 similar panicles showed 21 

 per cent of the spikelets blasted. Experiments carried on during the 

 summer of 191 8 indicate that this blasting is probably not due to the 

 bacterial disease but to the unusual meteorological conditions which 

 favored the development and spread of the bacterial blight. 



BACTERIAL ISOLATION EXPERIMENTS 



Oat plants showing typical lesions of halo-blight were collected from 

 fields around Madison, Wis., and from other points in the State, from 

 Tennessee, Urbana, 111., Lafayette, Ind., Wooster, Ohio, Davis, Calif., 

 and Arlington Farm, Va. Twenty-eight isolations were made from these 

 lesions, and 36 isolations from halo lesions produced by inoculations 

 in the field and greenhouse. Most of these isolations were from leaf 

 lesions, but a few were made from lesions on glumes (PI. 29). 



The first isolations were made by washing the leaf tissue through 10 

 sterile water blanks, crushing on a sterile slide, transferring to broth, and 

 plating from this broth suspension. Later isolations were made by 

 dipping the tissue for a second in 95 per cent alcohol, then into i to i ,000 

 mercuric chlorid (HgClj) for one minute, washing through three sterile 

 water blanks, and proceeding as in the earlier method. This later method 

 proved to be more satisfactory, but a comparison of the results from 

 both methods proved interesting. 



From all these isolations, with the exception of two from glumes, typi- 

 cal white colonies of the halo organism were obtained. These appeared 

 on potato agar in from i to 3 days. When the first«method of isolation 

 was used, without sterilizing the surfaces of the tissues, yellow colonies 

 appeared on the plates with the white colonies in 25 per cent of the 

 isolations from natural infections and in 22 per cent of the isolations 

 from inoculation experiments. When the surfaces of the lesions were 

 sterilized in mercuric chlorid for one minute no yellow colonies were 

 obtained. Twelve isolations were made from natural infections, using 

 mercuric chlorid ; and a still larger number were made from lesions due to 

 inoculation experiments. One set of isolations was made by placing the 

 leaf tissue in the mercuric chlorid for only 30 seconds. This leaf tissue 

 had been sprayed with a mixed culture of yellow and white organisms. 

 Yellow colonies appeared on the plates with the white colonies, but the 

 yellow colonies were not nearly so numerous as on plates poured from 

 tissue which had not been sterilized If the tissue had remained in the 

 mercuric chlorid for 60 seconds instead of 30 seconds no yellow colonies 

 would have appeared. These yellow organisms appear to be surface 

 saprophytes and do not occur within the tissues. 



The yellow colonies were mostly of one kind, judged by their appear- 

 ance on agar plates — round, smooth, shining, lemon-yellow with entire 

 margins — and they appeared on the potato agar in from one to two days. 

 This type of colony was chosen for inoculation experiments. 



