STEWART'S DISEASE OF SWEET-CORN (MAIZE). 



133 



Fig. 60.* 



This organism grows slowly on gelatin without liquefaction. In a stab-culture in 

 nutrient gelatin No. 478 at the end of 41 days, at 17 to 22 C., there was a thin line of 

 growth along the needle-track, best toward the top, and a dense, rather dry, slightly rough- 

 ened, bright, buff-yellow surface growth 7 mm. in diameter. Fig. 61 a shows its appearance 

 in gelatin stabs. 



In -f 10 nutrient gelatin, in rather thin sowings in Petri-dish poured-plates, at the end 

 of 7 days, at 10 to 20 C., the surface colonies of Bacterium stewarti under the 

 Zeiss 1 6 mm. objective and 12 comp. ocular were small, not perfectly circular, 

 not uniformly granular, more or less finely fissured, the margins not entire 



and sometimes even more or less decid- 

 edly notched ; the buried colonies were 

 globose-lobulated and less than i mm. 

 in diameter. This may not be a con- 

 stant phenomenon. 



In streaks on Loeffler's solidified blood-serum 

 Bact. stewarti made a good bright buff-yellow growth, 

 but without liquefaction. The cultures were under 

 observation for 32 days. 



On agar plates it grows slowly, forming small 

 round yellow colonies, the buried ones being very 

 small. In agar streak-cultures it gives a smooth trans- 

 lucent yellow slime which is usually paler than that of 

 Bact. hyacinthi (fig. 62), and frequently lobed on the 

 margins. Old streak-cultures are usually thin and 

 somewhat dry, and the older bacterial layer generally 

 baars numerous small raised, wet-shining, yellow colo- 

 nies on its surface. Jagged X-shaped crystals and 

 short prismatic crystals are not uncommon (fig. 63). 

 In agar stab-cultures at the end of 16 days there 

 was a moderate growth the whole length of the needle- 

 track and a distinct surface growth some millimeters 

 in diameter. Even where there were several stabs in 

 one tube the growths did not cover the entire surface 

 of the agar or coalesce ; the color was between saffron- 

 yellow and deep chrome (Ridgway). At the end of 5 

 weeks the surface growth was a deep yellow and not 

 at all viscid ; there was a good growth the whole length 

 of the stab; the agar was unstained, and there were 

 prismatic crystals in the upper part of it. At the end 

 of an additional 9 weeks, during which the cultures 

 were in the refrigerator, the surface growth was chrome 

 yellow. 



In stab-cultures in nitrate agar (stock 718) the 

 organism made a good growth, the surface layer being at first whitish. At the end of 24 

 days the agar was not stained, and no gas had been formed in the agar. A few crystals 

 were present in the uppermost layers of the agar. The stab had made a good growth the 

 whole length, but it thinned out slightly toward the bottom. There was a very distinct 



Fie. 60. Flagella of Bacterium stewarti. Stained by van Ermcngem's method from dilute Uschinsky's solution. 

 Slide*. August 7, 1904. 



tPic. 6t. a. Gelatin stab-cultures of Bacterium stewarti after 10 days at about 20 C. Gelatin not liquefied. 

 b. Gelatin stab-cultures of a non-pathogenic yellow liquefying organism from the surface of sweet-corn kernels. Sum- 

 mer of 1908. Two-thirds to three-fourths liquefied. 



Rg.6l.f 



