WILT-DISEASES OP TOBACCO. 



229 



only recently diseased. Nothing resembling the Bacillus nicotianae Uyeda or the large 

 micrococcus of van Breda de Haan was observed. Only a few of the many plants received 

 from North Carolina were used for making poured plates. The foliage was removed from 

 the remainder and the plants (most of which were in early stages of the disease) were then 

 set out in a hothouse belonging to the U. S. Department of Agriculture, and carefully 

 watched. For some weeks they showed no further indications of disease. They rooted 

 readily and made new leaves. Afterwards all of these plants developed further signs of 

 wilting (Vol. I, pi. 27, left fig.) and finally perished of this disease, the pith being rotted 

 out as in the Sumatran disease. The vascular ring in these plants was stained dark brown 

 or black, and the parenchyma was also blackened in 

 places, both in the interior and on the surface of the 

 green stems. In some instances cracks or cavities ap- 

 peared on the surface, opening into the depths of the 

 stem, and the tissues in and around these fissures were 

 blackened. The bacteria were present in the diseased 

 tissues in enormous numbers. 



When the plants had died they were removed and 

 healthy tobacco plants grown from seed sown in the 

 Department houses were set in their place. Theseplants 

 were some months old and naturally the root-system was 

 wounded considerably in transplanting them. To the 

 writer's surprise all of these plants (a dozen or more) 

 contracted the disease within a few weeks and finally 

 died of it. The checks left in the other house remained 

 free from the disease. 



Starting with single colonies of the North Carolina 

 organism obtained from the Petri-dish poured plates, 

 subcultures were made, and from these subcultures 

 healthy tobacco plants in another house were inocu- 

 lated in considerable numbers by needle-punctures in 

 the stem or leaf. These plants readily contracted the 

 disease, going through the same progressive stages as 

 the plants obtained from the field. All the character- 

 istic signs were present in these inoculated plants, one of 

 which was figured in Volume I (pi. 27, right fig.). For the 

 appearance of the remainder see plates $$ and 36. From 

 the interior of several of these plants the organism was 

 again obtained in pure culture by means of Petri-dish 

 poured plates, and with colonies from these poured 

 plates, or rather with subcultures therefrom, the dis- 

 ease was obtained in tobacco plants a second time by needle-puncture inoculations. These 

 were stem-inoculations on plants 13 to 36, most of which contracted the disease, but only 

 slowly, i. c, not until they had become large plants. They were inoculated September 23, 

 1905, and up to the middle of January the signs were confined to yellowing and loss of 

 the lower leaves, with the exception of one plant, which collapsed entirely (pi. 38). The 

 affected leaves developed pale green spots and then dried out very irregularly. Often the 

 "ears" died first, as described by van Breda de Haan; sometimes the apex died first (fig. 119), 

 or one margin (pi. 34), or the leaf dried out irregularly (pi. 35). In all such cases the 



*Fig. 118. Fusarium fruiting on the surface of a diseased tobacco stem in pinkish, pustular lines. Possibly 

 McKenney's tobacco Fusarium. A secondary infection and the only case that occurred in the house. Plant inocu- 

 lated on Sept. 23, 1905, with the North Carolina tobacco bacterium. Photographed Feb. 20, 1906. Stem dead. X2. 



Fig. 118/ 



