58 Walter H. Burkholder 



Nitrate reduction. There is no reduction of nitrates to nitrites. The 

 organism was grown in nitrate broth, and was tested with sulfanilic 

 acid and a-naphthalamine in acetic acid at the end of two, four, and 

 eight days. Positive results were obtained with Esch. coli. 



Hydrogen-sulfide production. A good growth is obtained on Wilson's 

 medium, but there is no positive reaction. On lead-acetate agar, at 

 the end of a month there is a very slight browning along the stab. 



Chromogenesis. The organism produces a water-soluble green fluorescent 

 pigment on various media. This pigment is the most noticeable in 

 Uschinsky's solution; it appears on beef-extract agar and on beef- 

 infusion agar, but not in Fermi's solution. A recently isolated organism 

 produces the pigment better than do the older strains. 



Loss of virulence. When the New Jersey strain of this pathogene was 

 first isolated, its virulence was exceedingly high. When it was inoculated 

 into a bean seedling or a young plant, the disease progressed rapidly and 

 the plant was killed in approximately a week. The invasive ability of 

 the pathogene, however, gradually diminished in pure culture, until at 

 the end of eight or nine months it was able to produce only a small 

 lesion on a bean seedling. Its ability to produce a pod spot was not 

 reduced so greatly. In May, 1927, the organism was inoculated into a 

 pod of the sieva bean (Phaseolus lunatus). This pod was kept in the 

 laboratory in a dry condition until October of the same year, when the 

 pathogene was reisolated. It was found then that the organism had 

 regained its former virulence. This process was repeated several times 

 during the winter of 1927-28 with the organism, so that its virulence 

 might be retained and it might be used in conducting inoculation 

 experiments. 



Thermal death-point. Test tubes of a uniform thinness, and containing 

 approximately 10 cubic centimeters of beef-extract broth (pH 7.1), were 

 used. Two large loops full of a broth culture twenty-four hours old 

 were added to the tubes, and the tubes were immersed in a water bath 

 for ten minutes. The water was kept agitated, and accurate temperature 

 readings were made continually with a certified thermometer graded 

 in tenths of degrees. The thermal death-point appeared to be approxi- 

 mately 49° C. 



Nomenclature 



It has been pointed out by the writer in a previous article (Burkholder, 

 1930) that the green fluorescent bacteria which cause plant diseases are a 

 rather closely related group. It is not surprising, then, to find that the 

 pathogene under consideration here agrees so closely in its cultural reactions 

 with one of the nineteen or more previously described species. The species 

 to which it is very closely allied is Phytomonas vignae, which also attacks 

 certain leguminous plants. There are several distinct differences between 

 the two pathogenes, however, both in cultural characteristics and in host 



