8 Walter H. Burkholder 



to rejuvenate all strains of pathogenes which had been in pure culture for 

 a year or more. This was done by growing them for several months in 

 their natural habitat, that is, as pathogenes on the bean plant. It is felt 

 by the writer that in comparative studies, especially with fungi, many of 

 the so-called physiologic species are brought about merely by the various 

 lengths of time during which the organism was grown in pure culture. 

 The writer has shown that this is the case with the fungus Fusarium martii 

 f. sp. phaseoli, and that a return to the natural habitat will cause a return 

 to the original morphologic and physiologic state (Burkholder, 1924). It 

 was hoped that this would hold true also with the bacterial pathogenes. 



In the preparation of media, stains, and other materials, and for their 

 method of use, the Manual of Methods for Pure Culture Study of Bacteria, 

 issued by the Society of American Bacteriologists, was followed unless 

 otherwise stated. The formulae for preparing Uschinsky's solution, 

 Fermi's solution, and Cohn's solution, were obtained from Smith's Bacteria 

 in Relation to Plant Diseases. Andrade's indicator was used in all the 

 sugar broths. To determine cellulose digestion, a broth containing 0.2 per 

 cent of peptone and 0.1 per cent of K 2 HP0 4 was used, in which was 

 placed a narrow strip of filter paper extending above the medium. In 

 determining the color of pigment production of an organism in or on any of 

 the media, Ridgway's Color Standards and Color Nomenclature was employed. 



Variations occurred in the same strain in different lots of media made 

 according to the same formula but with ingredients from different sources. 

 While this was true to a certain extent with beef-extract agar, it was very 

 evident at times with gelatin. The most striking cases are recorded later 

 in this memoir. 



In studying the bacteria, all cultures, with the exception of gelatin, were 

 kept in an incubator at a constant temperature of 27° C. Gelatin cultures 

 were incubated at 21° C. The 27°-C. temperature was decided on through 

 the observation that all cultures thrived well at that temperature. Some 

 of the organisms, however, appeared to grow equally well at a somewhat 

 lower temperature. 



In measuring individual cells the Congo red negative stain was used as 

 described by Benians (1916). It was felt that for the careful study of 

 morphology, and especially of size, results obtained by the direct staining 

 methods are less nearly accurate. 



THE BACTERIAL BLIGHT OF THE BEAN CAUSED BY PHYTOMONAS 



PHASEOLI 



Although a bacterial disease of beans was reported as early as 1892 both 

 by Beach (1893) and by Halsted (1893), Smith (1898) was the first to 

 isolate a bacterium from the bean, prove its pathogenicity, and give the 

 organism a name. First described as Bacillus phaseoli, references to the 

 pathogene may be found in literature under the following generic names 



