1923] 



. JENNISON — POTATO BLACKLEG 31 



The following strains were tested: Nos. 160.1, 170.3, 180.2, 

 183.2, 187B.1, 191, 195, 196, 197, 198. All responded and grew 

 very similarly, except No. 191. In the case of the other 9 strains 

 a considerable browning of the tissue approximate to the lines of 

 inoculation was plainly visible at the end of the first day. A 

 small quantity of dark brown to black liquid collected adjacent 

 to the line of growth. By the end of a week abundant develop- 

 ment of the cultures had taken place, forming a grayish white 

 slime surrounded by a dark-colored border. The tissues at the 

 margin of the growth were dark brow T n to black in color. Un- 

 derneath the bacterial growth they were somewhat collapsed, so 

 that the culture was growing in a shallow depression. No growth 

 took place on the uninoculated slabs kept as controls. 



Agar colonics (tubes inoculated at 28° C). — Colonies rather small 

 (3-15 mm. in 15 days); growth moderately rapid; form round to 

 somewhat irregular; surface smooth; elevation raised and flat; edge 

 entire, becoming undulate or lobed; internal structure, when magni- 

 fied about 50 times, finely to coarsely granular; chromogenesis none; 

 submerged colonies small, biconvex to ovoid, or nearly round ; color of 

 medium unchanged. 



In strain No. 191, the colonies were large; surface smooth; 

 elevation effuse; edge erose; and internal structure fine. This 

 was the only one of the 11 planted in agar plates that developed 

 markedly different features. In fact, one is led to the belief that 

 no more than 1 species could possibly be represented by the 10 

 strains in question. 



Gelatin colonies (incubated at 18-23°C). — Form round to some- 

 what irregular; edge entire, often becoming undulate; liquefaction 

 first noticeable, as a rule, about 24 hours after planting, proceeds 

 rapidly, and is saucer-shaped; chromogenesis none. 



Here again the cultural features and the physiological re- 

 sponse as manifested by liquefaction were identical for all strains, 

 except No. 191. In this case there was no liquefaction, and the 

 colonies were larger. At about 21° C. colonies developed quite 

 promptly in gelatin, and averaged 5-20 mm. in size, which was 

 considerably larger than the agar colonies. 



Gelatin stab. — Growth best at top; line of puncture filiform, often 

 slightly beaded; liquefaction begins in about 24 hours and at 20°C, 

 at first crateriform or napiform, becoming infundibuliform or strati- 

 form, complete as a rule at end of third week, when culture is aerated 

 by shaking occasionally ; the liquid gelatin becomes cloudy and often 

 a ring; sometimes a pellicle develops on the surface. 



