158 Journal of Agricultural Research voI.xix,no.4 



determined by the colorimetric method at the end of 6 weeks. The Pg 

 for dextrose was for maltose 5 to 5.2, for saccharose 4.6, for lactrose 7, 

 for glycerin 4.8, and for mannit 6. Controls and Bacillus coli Escherich 

 showed a Pg of 4.8 throughout. 



Temperature relations. — The maximum temperature for growth is 

 above 38° C. The minimum temperature for grov/th is 3°. The 

 optimum temperature for growth is 24° to 25°. The thermal death 

 point is 48° to 50°. Tests were made by the same methods as those 

 used for the halo organisms. 



Vitality on culture media. — The organism lives for 2 months on 

 beef-peptone agar at room temperatures. It is nonpathogenic. 



Group number. — The group number is 221.3333533, according to the 

 descriptive chart of the Society of American Bacteriologists. 



TECHINAL DESCRIPTION 



A motile rod, with rounded ends, one polar flagellum or several, single or occasion- 

 ally in short chains; average measurement 3.5 by 1.4 ju; no spores, pseudozoogloeae, 

 or involution forms; facultative anaerobic. On beef -peptone agar the colonies are 

 round, raised, smooth, lemon-yellow with entire translucent margins; deep colonies, 

 lens-shaped and opaque. Liquefaction of gelatin begins in 2 days and is complete 

 in 40 days. There is reduction in litmus milk in 24 hours and delayed curdling with- 

 out subsequent peptonization; milk is curdled in 3 weeks without subsequent peptoni- 

 zation; ammonia production moderate; indol production feeble; does not produce 

 hydrogen sulphid or other gas; no diastasic action on starch; grows moderately in 

 Uschinsky's solution, and very copiously in Fermi's solution. Growth slight in 

 Cohn's solution. Maximum temperature for growth is above 38° C, minimum 3°, 

 optimum 24 to 25°, thermal death point 48° to 50°. Tolerates sodium hydroxid 

 to below —22 Fuller's scale, and hydrochloric acid to -|-2o Fuller's scale. The opti- 

 mum reaction for growth is -I-5 Fuller's scale. Gram-negative; not acid-fast; stains 

 readily with carbol fuchsin, gentian violet, and methylene blue. Nonpathogenic 

 to oats. 



OVERWINTERING AND DISSEMINATION 



There is evidence from three sources that the organism causing halo- 

 blight winters over on the seed: (i) the presence of typical halo lesions 

 on the glumes and lemmas of maturing spikelets (Pi. 29) ; (2) the early 

 appearance of the disease on seedlings grown on soil not previously 

 sown to oats (PI. 28) ; and (3) the great difference in am.ount of blight in 

 oat plots from treated and untreated seed. 



(l) NATURAL AND ARTIFICIAL INFECTIONS OF SPIKELETS 



In 1 91 8 at the time the oat plants were heading out it became evident 

 from obser\^ations of the plot of Wisconsin No. 14 and from artificial 

 inoculation of Wisconsin No. 7 that the spikelets were also susceptible 

 to infection with the halo organism. After the Wisconsin No. 7 plants 

 had headed out a number of uninjured heads were sprayed with a water 

 suspension of the organism. Another bundle of heads, bruised by draw- 

 ing between the fingers, was similarly sprayed; and both were covered 

 with glassine bags for two days. When the bags were removed infec- 

 tions were already appearing on the bruised spikelets as light green 



