COBB'S DISEASE OF SUGAR-CANE. 



No pellicle, no pseudozoogloeae, very scant whitish rim (6 tubes), precipitate yellowish, 2 

 mm. broad, growth feeble. The optimum temperature is probably 30 C., or a little below. 

 Greig Smith reports growth at 30 C. much better than at 25 C., and also considers 30 C. 

 the optimum temperature. 



Greig Smith found the most suitable medium for the growth of this organism to be neu- 

 tral cane-juice gelatin (p. 34, Proc. Linn. Soc., 1902 ; but on p. 38 he says that very faintly 

 acid cane- juice gelatin is best), and the next best, ordinary glucose-gelatin, and slices of 

 potato. He describes its growth on suitable solid media as occurring in the form of "raised 

 yellowish patches which have the appearance and consistency of softened yellow beeswax. 

 When treated with water the culture slowly mixes, forming what appears to be a partial sus- 

 pension and partial solution." 



Another excellent medium is: 0.5 peptone, 5.0 saccharose or levulose, 0.5 [di?] potas- 

 sium phosphate, 2.0 agar, 100 tap-water. Acidity of 10 c.c. =0.14 c.c. tenth-normal acid 

 [ + i-4 Fuller's scale]. On this medium the organism grew most luxuriantly (RGS.). 



TABLE 5. Thermal Death-point Experiments. 



Portions of solid cultures put into bouillon and heated might be protected, perhaps, to a slight but sufficient 

 degree by non-conducting air inclusions. 



The vitality on culture-media varies greatly, of course, with the medium and the temper- 

 ature. The length of time the organism can live in the stem is not known. The first sugar- 

 cane received by the writer from Australia (1891) was 5 months on the way (detained in a 

 custom-house) and contained no living yellow organisms when it reached me, although the 

 bundles were full of the yellow slime ; but in a second shipment, which arrived from Australia 

 in a much fresher condition, the organism was alive. The ends of these canes were sealed 

 with sealing wax, and the canes were en route not more than 6 weeks. The organism was 

 dead in two inoculated stems at the end of 8 months. These were plants 30 and 36, purple 

 canes, which had not suffered from the disease. Some of the vessels of the stem snowed 

 immense numbers of bacteria, however, and a good-sized piece of this tissue was cut out 

 with a cold knife, thrown into 10 c.c. bouillon for an hour, then mashed with a sterile glass 



