BV 11. GREIG SMITH. 33 



however, enabled Cobb to recognise it as a new species, to w^iicli 

 he gave the name Bac. vascularum. 



In an investigation into the pathogenicity of the organism 

 Cobb"^ inoculated five apparently healthy canes with the gum 

 and retained one as a control. Unfortunately the control cane 

 was lost, and of the others four were gummed and one died. In 

 the four stalks that were gummed, the gummosis was most marked 

 in the neighbourhood of the point of inoculation. But as all the 

 canes in the stools developed gummosis there is the probability 

 that the inoculated canes would also have become affected inde- 

 pendently of the inoculation. The fact that gummosis was most 

 marked in the neighbourhood of the site of inoculation indicates 

 that the gum probably set up gummosis; but like the majorit}^ of 

 plant infection experiments the result of Cobb's experiment is not 

 decisive. Even if the experiment had been most satisfactory it 

 would onl}^ have shown that cane-gum could produce gummosis, 

 and thus the pathogenicit}^ of the bacterium itself would remain 

 doubtful. In all infection experiments the recognised and legiti- 

 mate method is to purify the bacterium by growth in plates of 

 artificial media, and after it has been proved that the bacteria 

 are undoubtedly pure by their constant appearances of growth, 

 etc., upon one medium, to employ the pure culture for purposes 

 of inoculation. 



The Method of Research. 



The cause of the gummosis of the cane, therefore, appeared to 

 be sufficiently undecided to warrant a thorough investigation, 

 and I decided to attack the problem from the side of the gum 

 rather than the plant— a method that has not been previously 

 tried, and one which promised to give more conclusive results 

 than could be hoped for with infection experiments. If a gum 

 could be produced in the laboratory from a bacterium isolated 

 from the cane, and if it were identical with the gum obtained 

 from diseased canes, then the bacterial origin of the gum and the 



Cobb, Agric. Gazette of N,S. Wales, 189i. 



