3i6 



BACTERIA IN RELATION TO PLANT DISEASES. 



between the vessels as shown in plate 1 7 or may affect the wall of the vessel itself. When 

 located in the vessel the lignified parts absorb the stain. 



In many large cabbage stems the writer noted a decided increase in the number of 

 chlorophyll bodies in tissues immediately surrounding the bacterially infested vessels. 

 Frequently the green color was as conspicuous as the brown stain. Without knowing 

 positively, the writer has been inclined to regard this phenomenon as brought about by the 

 osmotic movement of food stuffs toward the bacteria, and by the liberation of unusual 

 amounts of carbon dioxide as a result of the bacterial multiplication. The same phe- 

 nomenon occurs in the tumor-strands in crown-gall of the daisy (Circular 85, p. 3). 



THE PARASITE. 



As already stated, the cause of this disease is Bacterium campestre (Pammel) EFS,* 

 a yellow one-flagellate Schizomycete (fig. 121). It is sometimes motile when taken directly 

 from the plant and examined in a hanging drop of water, but more often not, especially if it 



Fig. IH-t 



is takenfrom partswhich have been occupied for some time (see B. tracheiphilus, pp. 221, 242). 

 It is a rather small and somewhat variable organism, especially in old growths. When 

 crowded in the plant or when taken from old cultures, it often much resembles a coccus, 

 i. e., it is a very short rod with rounded ends (Vol. I, fig. 18). When multiplying rapidly in 

 the plant or when taken from young cultures it is a rod usually one and a half to four times 

 as long as broad (figs. 122, 123). In such situations it occurs singly or more often joined 

 in pairs, end to end, and usually with a distinct constriction; in some media short chains of 



*Syn. Bacillus campestris Pammel, Pseudomonas campestris (Pammel) EPS. The nomenclature of the bacteria 

 in this volume corresponds to my ideas on this subject as enunciated in Vol. I, to which the reader is referred. Potter 

 writes Bacillus campestris rutabaga. 



fFiG. 114. — Bacterium campestre occupying the intercellular spaces in the parenchyma of a turnip-root. Cross- 

 section of inoculated plant (No. 53). Protoplasmic contents of cells omitted. The bacteria have crowded the cells 

 apart somewhat, but are still confined to the intercellular spaces. A continuance of this multiplication and crowding for 

 a few weeks would result in the collapse of the cells and the formation of a cavity such as that shown in fig. 117. 

 Drawn from a photomicrograph. X475. 



