cobb's DISEASE op sugar-cane. 



51 



ing. Upon cutting the cane across many of the vascular strings were colored ; and finally the cotton 

 wool upon which the cane rested also became crimson from the red gum which had flowed down the 

 vessels of the strings. This experiment is, in my opinion, very significant as regards the combined 

 (symbiotic) action of the mould and bacterium in producing a red gum in the large vessels of the vas- 

 cular strings of the sugar-cane. 



Apparently the sugar-cane had been sterilized before inoculation. 



To the writer this means simply that the red pigment is produced by the fungus when 

 grown in an acid substratum and not when grown in a neutral or alkaline substratum. Noth- 

 ing is said about the production of acids by the Bacillus, but it is stated to be a gas-producer, 

 and from this we might infer the production of sufficient acids for this purpose. The phe- 



Fig. 21.* 



nomenon is not peculiar to this fungus, the writer having pointed out similar changes in 

 color 15 years ago in connection with his studies of species of Fusarium, some of which 

 remained white on alkaline media, but developed the most brilliant reds and purples on 

 acid media. f 



The writer observed no fungus in the red strands of his inoculated cane plants and 

 obtained on poured-plate cultures made therefrom, as already stated, only Bacterium vas- 



*Fig. 21. Cross-section of cane-stem (inoculated plant No. 6), showing three vessels occupied by Bacterium vas- 

 cularum. Other vessels (at left) and connective tissue free. One normal nucleus and what appear to be two distorted 

 nuclei are present. Fixed in 95 per cent alcohol. Slide 310 (2. 



fSee Wilt Disease of Cotton, Watermelon, and Cow-pea. Bull. No. 17, Div. Veg. Path, and Phys., U.S. Dept. of 

 Agriculture, Washington, 1899, especially pp. 13 to 30. 



