Nov. 15. 1919 Bacterial Blight of Soybean 183 



CULTURAIv CHARACTERS 



Unless otherwise specified, all cultures were incubated at 25° C, a tem- 

 perature very favorable for the growth of the organism. Reactions were 

 determined by titration with phenolphthalein as indicator, the trial solu- 

 tion always having been boiled previous to test. All references to reac- 

 tion of media are recorded in terms of Fuller's scale. Ridgway's color 

 standards * were used in the determination of color. 



Agar poured plates. — On potato agar, colonies appeared in about 

 48 hours and at the end of 5 days were from 2 to 5 mm. in diameter. 

 They were creamy white tinged with brown, circular, shining, and con- 

 vex with umbonate center. The margin in general was entire, although 

 it may be slightly lobed. The surface may show indication of irregular 

 wrinkling or beading in the central part, or there may be more or less 

 concentric and radiating convolutions throughout the colony with a 

 definite growth border.^ The consistency was butyrous. Buried colo- 

 nies were lenticular. 



On +10 beef-peptone agar, colonies appeared in about 48 hours and 

 at the end of 5 days were about 2 to 3 mm. in diameter. They were 

 circular, smooth, shining, and convex. The margin was entire, with no 

 noticeable surface irregularity. The colonies were creamy white in 

 color tinged with brown, butyrous in consistency, and showed a definite 

 browning of the medium around them. This brown color (chestnut) 

 later became general throughout the entire plate. Buried colonies were 

 lenticular. 



Agar stabs. — Stabs in potato agar when 2 days old showed a surface 

 growth about 6 mm. in diameter, rather flat, shining, and creamy white 

 tinged with brown. Later this growth may spread over three-fourths 

 to almost the entire surface. Definite but moderate growth followed 

 the stab. There was no change in the medium. 



Stabs in -|- 10 beef-peptone agar when 3 days old showed a surface 

 growth about 5 mm. in diameter, rather flat, shining, creamy white 

 tinged with brown, with slight browning of the medium to the depth of 

 the stab. Later the top growth may become more spreading, involving a 

 considerable part of the surface. Definite growth, a little more marked 

 than on potato agar, followed the stab. The medium finally became 

 quitfe uniformly browned. 



Agar slants. — On potato agar slants, stroke cultures made a mod- 

 erate, shining, flat, filiform to irregularly scalloped growth, creamy 

 white in color tinged with brown. More or less wrinkling may occur on 

 the surface. At low temperatures the growth was thicker and more 



> RiDGWAY, Robert, color standards and color nomenclature. 43 p.. Si col. pi. Washington, 

 D. C, 1912. 



' The irregularities are not always clearly evident to the naked eye. They show best under magnification 

 and when lighting is semidirect. There is also considerable variation in the degree of surface marking of 

 different strains of the blight organism (PI. 15). 



