'32 



BACTERIA IN RELATION TO PLANT DISEASES. 



until the third day. Surface colonies brown faster 

 than buried ones, which would seem to indicate 

 that air is necessary for the formation of the pig- 

 ment. The browning of surface colonies is distinct 

 at the end of 15 days.* Stab growth is best in 

 upper part of the agar. On slant agar during the 

 first 10 days there is a thin, white, smooth, wet- 

 shining streak and a small amount of white pre- 

 cipitate in the fluid of the V. There are no crystals 

 and no stains in the agar. The surface colonies on 

 nutrient agar incline to be irregularly round. Only 

 a few of the colonies are perfectly circular, but at 

 the same time they are not lobed or fingered. They 

 are wet-shining and smooth; ringed growths are 

 sometimes visible in the colonies. The general ap- 

 pearance of the colonies on agar plates is shown in 

 plate 37. 



The brown pigment from the tobacco organism 

 grown on agar or potato is soluble in water, ethyl 

 alcohol (absolute), and glycerin, but not in chloro- 

 form, turpentine, xylol, benzine, petroleum ether, 

 rhigolene, or benzole. 



Gelatin stabs. No liquefaction; not even after 

 several weeks. Growth slight at 14 C. (For 

 kind of gelatin used see Vol. I of this monograph.) 



Potato. Much like Bacterium solanacearutn 

 (pi. 41 , fig. 4). Very milky turbid growth in fluid 

 around potato during the first 10 days. Old 

 browned potato cylinders when mashed in an 

 abundance of diluted alcohol-iodine gave a deep 

 purple-blue reaction. In another test the color 

 reaction of the mashed potato cylinders is recorded 

 as "deep purple." 



Standard ( + 75) peptonized bouillon. After 20 

 days, no pellicle, little or no rim, slight in one or 

 two tubes but not black , uniformly and well clouded , 

 with about 10 mm. breadth of dirty gray-white 

 precipitate. The cloudy bouillon does not now 

 look turbid (flocculent) to the naked eye. A pencil 

 is barely perceptible behind two of these tubes ; it 

 can not be seen behind three of them.f Bouillon 6 

 days old bore no conspicuous rim or pellicle, but 

 there was a moderate amount of gray-white pre- 

 cipitate and considerable turbidity in the fluid, 

 which was filled with hundreds of small pseudo- 

 zoogloese. The bouillon was not browned. 



Acid bouillon (+JJ muscle-acid, dried out some- 

 what). The organism was retarded somewhat at 

 first, but then grew readily. On the third day tubes 

 of this bouillon were distinctly less cloudy than 

 tubes of + 15 nitrate bouillon (one-third to one-half 

 as cloudy). There was no rim or pellicle in either 

 bouillon at this date. After 56 days, the brown- 

 ing of the acid bouillon was much the same as with 

 Bacterium solanacearutn from the potato plants, 

 and there was about the same amount of dirty 

 brownish- white precipitate. No pellicle and not 



*I5rowned colonies of the Florida organism from tobacco were dead after about two weeks. On April 22, 1909, 

 the vitality of 6 brown colonies from an agar plate of March 30 (North Carolina organism) was tested by copious trans- 

 fer to beef-broth. These colonics had been brown for several days. Of the 6 colonies 4 finally clouded the bouillon. 

 Of [8 browned colonies on agar (Fla. potato, 1914) 8 were dead at end of 21 days. 



t'fhe tcsl 1 11I 1. used in the laboratory of Plant Pathology are about 16 to 18 mm. in diameter, and of non-soluble 

 glass obtained from Greiucr and Friedrichs, Stutzenbach, Germany. 



JFig. 123. Aerial roots which developed on tobacco-stems inoculated with the North Carolina bacterial tobacco 

 organism. Inoculated Sept. 23, 1905. Photographed Feb. 21, 1906. Such roots do not ordinarily occur on the stems. 



