230 



BACTERIA IN RELATION TO PLANT DISEASES. 



vascular bundles at the base of the green midrib were browned and occupied by the bacteria. 

 Cavities were formed in the midribs of such leaves. This browning and bacterial occupa- 

 tion was not confined, however, to the petiole or base of the midrib, but could be traced 

 through the latter for a distance of i to 2 feet. In some cases also the browning and 



bacterial occupation were traced out 

 into branches of the midrib. The 

 appearance of some of the blackened 

 midribs in cross-section and of similar 

 petioles in longitudinal section is 

 shown in figs. 1 20, 121. Poured plates 

 made from the brown slush in the 

 hollow stem (pi. 38) showed the pres- 

 ence of an intruding soft white-rot 

 organism, as was anticipated (fig. 

 122), and the inoculated bacterium 

 was not made out clearly. 



The blackening and partial de- 

 struction of the pith in two of these 

 inoculated plants is shown on plate 

 39. Similar results obtained by inoc- 

 ulating Bact. solana.cearumpla.ted from 

 a potato are shown on plate 40. 



There was in some cases an abnor- 

 mal pushing of roots from inoculated 

 stems (fig. 123), the same as in tomato 

 plants inoculated with Bad. solana- 

 cearum (pis. 27, 28). 



Studies carried on at the same 

 time, and afterward, indicated that 

 the cultural characteristics of this or- 

 ganism, so far as tested, did not differ 

 materially from those obtained with 

 Bacterium solanacearum plated from 

 diseased potato and tomato stems 

 obtained from various parts of the 

 United States. On the other hand, 

 cross-inoculations from tobacco to 

 tomato and from potato to tobacco 

 were not particularly successful. The 

 tomatoes inoculated with the tobacco 

 organism developed adventive roots on 

 the stem, but no wilt appeared. The 

 tobaccos inoculated with the potato 

 organism did not wilt or show other 

 external signs of disease, but the strain 

 used was not a very virulent one. 

 The following are the morphological and cultural characters of the North Carolina 

 tobacco organism, so far as determined in my laboratory: 



Fig. 119. 



"Fig. in). Dark veins and large <h v brown spot on a tobacco leaf attacked by tin- Granville tobacco wilt. Infec- 

 tion by nay df the vascular bundles of the petiole. Plant inoculated mi the stem Any. 5, 19ns, from a diseased tomato- 

 stem Photo .: iphi il \ 1 1 . 1 1 .1 .'7. 



