17 



bo free from outsicU' contain i nation was used. WhenoviT there was 

 the slightest doubt as to its })urity it was either discarded or the tubes 

 were marked •"contaniinatiHl." Freiiuently tul)es marked in this way, 

 howeA'er, remained free from any organism. In cultures made from 

 spots which had collapsed various fungi and l«icteria were occasionallv 

 obtain<>d, but this was not constant nor were the organisms alwaj's of 

 the same sort. Cultures including the epidermis freiiuently con- 

 tained various organisms, among these being a yellow bacterium, 

 which occurred frequently on the surface of both diseased and healthy 

 leaves. The morphological characters of this bacterium and its 

 groAvth in the various media, with the exception of acid gelatin and 

 agar, agreed well with Bactrrium dinnthl as described by Arthur and 

 Bolle}'. On the two media mentioned the colonies were surrounded 

 by a peculiar light band, which was at iirst thought to be some con- 

 taminating organism, its structure being like exceedingly minute cocci, 

 the largest less than live-tenths of a micron in diameter. Attempts 

 were made to cultivate this supposed organism on various media, but 

 all failed, and even with the two media mentioned it was not possible 

 to obtain a colony of the yellow germ which was not accompanied by 

 this peculiar external formation. On neutral or alkaline media, how- 

 ever, no such change took place. Further inxestigation showed that 

 these coccus-like bodies w^ere made up of something precipitated from 

 the culture medium by the alkali which the germ produced. Nothing 

 of this kind was described for Bacterimn dianthi bv Arthur and 

 Bolley. 



INFECTION EXPERIMENTS IN 1897. 



As the orange yelloAV germ agreed in most respects so closely with 

 Bacterium, dianthi and as no other yellow organism that could possibly 

 be confused with B. dianthi was found in the hundreds of leaves 

 studied, it was determined to make special use of this germ for infec- 

 tion experiments, but several other common forms were also used, the 

 principal one among these being a white organism which liquefied 

 gelatin readil}^. 



Great difficulty was experienced in finding healthy plants with which 

 to work. Those finally selected were taken into the laboratory, thor- 

 oughly freed from aphides and thrips, and allowed to grow under moist 

 bell jars for three weeks. During this time the disease developed in 

 some of the leaves which were apparently healthy when brought into 

 the laboratory. The spots in such case were marked with India ink 

 so that they would not be confused with spots that might result from 

 infections. After the period of incubation had passed and a series of 

 plants had been obtained which were reasonably free from spots, and 

 also from aphides, thrips, and red spiders, rapidly developing fluid 

 cultures of the germ were thoroughly brushed into the surface of the 

 17692— No. 19 2 



