5Q 



BACTERIA IN RELATION TO PLANT DISEASES. 



B. pseudarabinus. This is peritrichiate and non-sporiferous, liquefies gelatin slowly, and 

 does not stain by Gram. He says of the fungus : 



In glucose-gelatin the mould produced a brilliant crimson-scarlet color, and it undoubtedly was 

 the agent which was primarily responsible for the color of the strings. But from the presence of gum 

 in the vessels I was of the opinion that the mould was accompanied by a slime bacterium, and that the 

 complete phenomenon of red gum was brought about by the simultaneous growth of two organisms, 

 a mould and a bacterium. This view was confirmed during the research. It may, however, be men- 

 tioned here that every portion of red vascular bundle that was taken did not contain the mould, but 

 did contain slime-forming bacteria ; and from this we must conclude that the mould does not accom- 

 pany the gum along the whole length of the string, but colors the gum which is carried along the ves- 

 sels, perhaps by sap-pressure, 

 perhaps by bacterial growth, 

 or that the rapid growth of the 

 bacteria starves out the mould 

 after the color has been pro- 

 duced. At any rate two things 

 are certain: (i) The mould 

 can, under certain conditions, 

 produce the color and cannot 

 produce the slime, and (2) the 

 bacteria do produce the slime. 



Greig Smith did not 

 reproduce this disease by in- 

 oculations into living cane. 

 The brilliant red pigment 

 produced on glucose-gelatin 

 did not form on levulose 

 agar. On this medium it 

 seldom produced a trace of 

 color, but, on sowing the 

 middle of a plate of nutrient 

 levulose agar with the fungus 

 and then the margin of one 

 side of the same plate with 

 his Bacillus pseudarabinus, a 

 brilliant red color appeared 

 as soon as the two organisms 

 fused, and this crimson color 

 developed not only through- 

 out the colony, but in the 

 neighboring region. He did 

 not get the same result when 

 Bad. vascularum was substituted for B. pseudarabinus. A colony of Bad. sacchari 

 developed a foxy-red color at the side toward the mould, and the medium was faintly 

 stained the same color. 



This bacterium grew upon fresh, sterilized portions of sugar-cane as white slime, while the mould 

 during its growth upon [other samples of] the same substratum produced practically no color [except 

 upon old portions of sugar-cane, where a red color is said to have developed], the older cultures 

 only showing spots of pinkish aerial hyphae, but when both bacterium and mould were grown upon 

 the [same] cane a deep crimson color developed upon the outside of the cane where the gum was form- 



*Fic. 20. Cobb's disease of sugar-cane. Introduced for comparison with fig. 19. The section is from the same 

 sinn. but in this bundle all the- vessels of the xylem are occupied by the bacteria. The thin-walled tissue immediately 

 above the vessels is phloem. Slide 121 (7. 



Fig. 20. 



