[JONES] STUDY OF SOME AZOTOBACTER 47 



verrucose with fine indentations and the black pigment is produced 

 earlier and is usually more intense. See PI. I, Figs. 6 and 8. 



Growth in Ashby's Solution. 



Cultures of each of the four varieties grown in Ashby's solution 

 in Erlenmeyer flasks at 25°C. produce a more or less flaky pellicle, 

 rather thick, easily broken when disturbed, an irregular rim rising 

 slightly up sides of flask and a cloudiness in the body of the medium 

 which may also obtain zoogloea flaky masses detached from the pellicle 

 which slowly accumulate at the bottom of the flask. The pellicle 

 produced by A^ and A^ is smoother and more moist than that produced 

 by A3 and A4, that of the latter being more flaky and somewhat dry 

 and granular, as compared with that of the former. After three or 

 four weeks, the pellicle and ring becomes brown and the body of the 

 medium becomes clear and pale golden in color, the pigment production 

 being least in A^ and greatest usually in A4. The pigment slowly 

 intensifies with age. 



Cultures in Various Media. 



(All four strains are alike in the following media) . 



Beef Extract Agar + 5°. 



Growth is restricted; surface colonies even when thinly seeded 

 do not attain a diameter greater than 2 m.m. After 24 hours at 25°C., 

 they appear as small round colonies .5 m.m. or less, greyish, thin, entire, 

 and finely granular under the lower powar lens, moist in consistency. 

 They attain their maximum size in three or four days, become light 

 brown in color, are very slightly raised, smooth surface and soon become 

 tough in texture, later becoming hard and adhering to surface of medium 

 like drops of dried varnish. Streak cultures are linear and have the 

 same characters for consistency and appearance as described for colonies. 



Beef Extract Bouillon + 5°. 



After seven days at 25°C., cultures of each variety show a light 

 granular pellicle, with occasionally a slight granular growth extending 

 irregularly down sides of tube, no ring, medium clear. After two 

 months, the appearance is the same plus a slight granular precipitate. 



Stab Cultures in Beef Extract Gelatin + 5°. 



No liquif action of the gelatin occurs. After two weeks at 20°C., 

 the growth is linear, finely serrate, greater at surface than in depth, 

 with a depressed nail-head growth at top, firm, almost horn-Jike in 

 consistency, and smooth. Pale brown color. 



