deti'ftod only a onuluul shrivi'lino- of the tissues of the leaves. At 

 tirst lig-ht-eolored blotches made their appearance, which gradually 

 extendt'd, coalesced, and finally the whole leaf became dry and life- 

 less." A further examination made b}^ Dr. Arthur in 1889 revealed 

 the presence of the semitransparent dots described. He says: 



Repeated microscopic examinations of the sections through these spots convinced 

 us that the cells of the region were always infested with bacteria — often in consider- 

 able numbers. It was not diflicult to see that the conspicuous dry blotches might l)e 

 derived from the incunspicucjus dots and that the latter possil)ly represented the 

 beginnings of a genuine disease. There were now a number of difficult questions to 

 answer, foremost of which was to show the causal or accidental relation of the bac- 

 teria seen in the cells to the degeneration of the tissues. The larger part of the work 

 of tlie investigation from this tin:;; on until the main facts were established — a period 

 of about eighteen months — fell to the lot of Mr. Bolley. 



ISOLATION OF THE GERM. 



Following' out the suggestions resulting from their microscopical 

 examinations, Arthur and Rollcv made an attempt to isolate the germ 

 supposed to l)e the cause of the trouble. It should be noted that their 

 "repeated trials for a ninnbin' of months gave such varying results 

 that nothing of a substantial natiu'e was learned. Saprophytic forms 

 from the air and from the leaves of the plant took possession of the 

 cultures, obscuring or destroying the slower-growing parasitic form." 

 However, the addition of malic acid to the culture media retarded the 

 growth of saprophytic bacteria and gave the slower-growing organisms 

 a chance to develop. One of the most constant sorts o})tained b}^ 

 Arthur and Bolley^ in this wa}" was a "coccus-like form of a yellowish 

 color that grew slowly, ))ut developed well in acid cultures," and this 

 the}" believed, as the result of infection experiments, to be the cause 

 of the disease in question. 



No spores were found in any stage of growth. The bodies discovered 

 in the cells of the host and believed to be bacteria agreed in size and 

 general appearance with Bacterium dianthi. The cells were not united 

 into filaments, but were almost or quite separate from one another, 

 exhil)iting no independent movement and undergoing no marked vari- 

 ation in form during growth. 



It is not nece'ssarj^ in this paper to enter into a full discvission of the 

 biology of this germ, but a few of the most important points may be 

 mentioned. In plate cultures of 10 per cent acid nutrient gelatin the 

 body of the colony is made up largely of zoogloea, giving an "irregular 



'They describe the species as "Bacterium dianthi Arthur and Bolley n. sp. Cells 

 oval to elliptical, single or rarely united, 0.9-1.25 by 1-2 /<.; in rich fluid media more 

 united, in part forming short filaments, at first motile, afterwards forming distinct, 

 elongated, somewhat convoluted zoogla?a; on solid media becoming yellow in mass. 

 * * * The color accumulates slowly as the bacteria grow and is apparently not 

 deposited within the cell, but is an excretion from it." 



