GEORGE K. K. LINK 597 



methylene blue. A transfer from such old cultures to fresh agar gave pearly white 

 growth composed of long rods which not infrequently present a beaded appearance. 

 He considers these forms as an "embryonic" stage. As the culture ages, the rods 

 break up, and finally after twenty days the rods are replaced by small faintly staining 

 cocci with slender bacilli or filaments. Eventually, as the zocgleal mass appears, all 

 cocci disappear. Spores or sporelike bodies also appear in cultures which germinate 

 when transferred to new media, and give rise to rodlike bodies not unhke Bad. 

 tumcfaciens in size. He suggests that this phenomenon may account for the differences 

 in size of rods noted in this organism by Smith, Brown, and Townsend,' Riker,' and 

 Robinson and Walkden.'' 



A less detailed report of evidence of cyclogeny is the preliminary paper by Nixon^ 

 on changes of B. amylovorus in the lesions it causes in apple trees. All of this work 

 should be repeated. In the meantime, it will be well for investigators to approach with 

 an open mind the disquieting and troublesome phenomena of degeneration, involu- 

 tion, and contamination of colonies. Much that has seemed incongruous may be 

 clarified. 



ROLE or ENVIRONMENTAL FACTORS IN INCITING COLONY OR CELL 

 CHANGES OF PLANT PATHOGENS 



Sharps was not able to correlate the appearance of rough colonies with any en- 

 vironmental factor. Apparently it was spontaneous. This is in line with a great body 

 of data from the animal field. He was, however, able to obtain smooth and rough 

 colonies from rough strains of Bad. phaseoH sojense after passage through the soy 

 bean. He found that Bad. phaseoli sojense was more rough on potato than on beef- 

 dextrose agar. 



There is a considerable body of data obtained incidentally, which however sheds 

 light upon the effect of environmental factors upon microbic dissociation. Hadley' 

 lists fifteen distinct factors which are reported as inciting dissociation of animal path- 

 ogens. Link and Hull' report the apparently spontaneous change of rough to smootii 

 cultures of Bad. citri and of Bad. tumcfaciens, and a change from smooth to rough in 

 Bad. medicaginis var. phaseolicola. No. 23. Bad. tumefaciens develops and retains 

 partially rough colonies more freely on beef-dextrose agar than on potato-dextrose 

 agar. 



Smith, ** incidental to discussions of cultural characters of Bad. tumefaciens, has 

 recorded data which probably are in point here. He points out that the colonies of this 

 organism which he considers characteristically wet, shining, and smooth remain so 



'Smith, E. F., Brown, N. A., and Townscnd, C. O.: "Crown Gall of Plants. Its Cause and 

 Remedy," U.S. Dept. of Agr. Bur. PI. Ind. Bull. 213. igii. 



^ Riker, A. J.: "Some Relations of the Crown Gall Organism in the Host Tissue," J . Agr. Re- 

 search, 25, iig-32. 1923. 



3 Robinson, W., and Walkden, H.: "A Critical Study of Crown Gall," Ann. Bol., 37, 299-324. 

 1923. 



■< Nixon, E. L. : "Migration and Transformation of Bacillus amylovorus in Apple Tissue," 

 Fhytopath., 16, 77. 1926. 



s Sharp, C. G.: loc. cit. ^Link, George K. K., and Hull, K.: loc. cit. 



^Hadley, P.: loc. cit. ^ Smith, E. F.: Bacterial Diseases of Plants. 



