40 



THE GUMMOSIS OF THE SUGAR-CANE, 



multiplication of the microbe. With 0-02% the stroke was 

 slow to show itself, was alwaj's very scanty, and finally, after 

 ten days' incubation, it dried up. 



The Location of the Bacteria. 



Cane-juice has an acidity equal to an amount of tartaric acid 

 varying from 0*2 to 0-3%, and as the juice is derived from the 

 tissue we can understand why the bacteria avoid these strongly 

 acid tissues and inhabit the slightly acid or neutral fluids of the 

 vascular system. 



In view of the fact that in many bacterial diseases of plants, 

 the microbes are found only in the vessels, and that the bacteria 

 are very sensitive to the reaction of the contents of the vessels, 

 it would appear that the immunity of plants disease-proof to 

 bacterial infection may depend upon a relativel}'^ greater acidity 

 or alkalinity of the vascular contents as compared with susceptible 

 varieties. 



A peptonised medium similar to that used in testing the 

 influence of peptone was employed in a small test to corroborate 

 the general conclusion that had been drawm during the work upon 

 the bacterium with regard to the temperature, and from the 

 growths upon the agar it was manifest that a temperature of 

 30° C. was best suited to the organism. 



The Optimum Temperature, 



That the bacterium grows rapidly at 30° C. (86° F.) and not 

 at all at 37°, serves to explain in part at least why the disease 

 occurs more frequently in cold, wet seasons. Such seasons check 

 the growth of the plant, the \ itality is lowered, and at the same 

 time the bacteria, being under favourable conditions of tempera- 



