BY R. GREIG SMITH. 



43 



grow disease-resisting varieties, as has been previously recom- 

 mended, not only for gummosis, but for other diseases. In this 

 relation it may be mentioned that there are one or two well 

 known varieties which have never been known to develop gum- 

 mosis. The best known of these sound varieties is Tanna, a stout 

 heavy cane, hard in the rind and containing a high percentage of 

 fibre. The sugar content is, however, not so high as it is in some 

 of the varieties which are liable to gummosis. Fields which have 

 yielded badly diseased crops, have, when planted with Tanna, 

 produced perfectly sound canes. 



In order to form a gum as it undoubtedly does, the bacterium 

 probably requires a carbohydrate, and although saccharose has 

 been employed and found exceedingly useful, yet it does not follow 

 that it is necessary, or that saccharose is the best carbohydrate. 

 Other sugars might give a better yield of gum. To test this 

 question, about half a gramme of various substances was added to 

 10 c.c. portions of a faintly acid medium containing peptone 

 0-5%, sodium phosphate 0*2%, potassium chloride 0*5%, agar 2%, 

 and after sterilisation of the tubes, the sloped surfaces were 

 inoculated and then incubated. 



This experiment showed that either dextrose, levulose, or 

 saccharose are absolutely necessary for the free growth of the 

 organism and the production of gum. The bacteria did not 

 grow in the presence of the other sugars and carbonaceous 



