44 THE OUMMOSIS OF THE SUGAR-CANE, 



matters, from which we infer that these cannot be utilised. Of 

 the three sugars, levulose and saccharose are more easily assimi- 

 lated than dextrose. 



The organism does not secrete invertase. This was shown by 

 the practical absence of invert sugar in the agar cultures. In 

 testing inversion fluid cultures are preferable, but as this bacteria 

 does not grow to anj^ extent in saccharose fluid media, an agar 

 culture had to be taken. The agar was melted and dissolved in 

 water, after which the solution was treated with basic lead 

 acetate, etc., as is customary in sugar determinations. Of the 

 saccharose in the tube originall}', onlj'' 3% had been inverted to 

 fruit sugar, a quantity which might easily have been produced 

 through the hydrolytic action of the small quantity of acid in the 

 medium. 



The Most suitable Medium. 



From these experiments we conclude that an excellent medium 

 for the growth of the bacterium and the production of gum would 

 have the following composition,: — 



Peptone ... ... ... ... 0-5 



Saccharose or levulose ... ... 5 



Potassium phosphate ... ... 0*5 



Agar 2-0 



Tap water 100 



Acidity of 10 c.c. =0*14 c.c. tenth-normal acid. 

 On this saccharose medium the bacteria grew most luxuriantly 

 .at the optimum temperature (30°), and since the organisms 

 grow so well, we cannot doubt that similar conditions as regards 

 nutrition, acidity, and temperature favour the development in 

 diseased canes. 



Bacterium vascularum, Cobb. 



Shape, d:c. — The organism appears as an actively motile, sh(jrt 

 rod, and when stained and imbedded in balsam has an average 

 measurement of 0*4 : 1 fx. Carbol violet followed by dilute 

 -iilcohol produces the best films ; fuchsin stains the gum, which 



