CANE SUGAR. 



seen to wilt ; on applying a steady tension this could be pulled out entire, or 

 in the case of a sprouting eye, the bud could be unravelled ; at the base of the 

 leaf a discoloured area was seen associated with a foul smell ; by examining 

 sprouting eyes which were just beginning to wilt, or even which were 

 apparently healthy, all stages of the rot could be seen ; in many cases there 

 was evidence of previous damage by an undetermined insect, the larva of 

 which (a footless grub, about T % inch long) was present ; but frequently there 

 was no sign of insect damage. This disease was certainly causing no 

 inconsiderable harm. 



4. The Gumming Disease. Pseudomonas vascularum. Cobb. This disease, 

 which has been incorrectly associated with Top Rot, was originally 

 described by Cobb in Queensland. It is characterized by the exudation 

 of drops of gum from a cut or punctured surface, as shown in Fig. 71. 



FIG. 71. 



The top of the cane also becomes charged with a putrid offensive slime. Cobb 

 connected the disease with the presence of a micro-organism which he called 

 Bacillus vascularum, but did not make the complete bacteriological proof of the 

 connection of this organism with the disease. This has been done later by 

 Erwin Smith, 36 who has definitely proved the connection between gumming 

 and Cobb's organism. An important point in Erwin Smith's research is that 

 he shows that the 'common purple cane' and D 74 are much less susceptible 

 than the 'common green cane,' and connects this with the less acidity of 

 the 'common green cane.' Greig Smith 38 also proved that the bacillus 

 grown in pure culture produced the characteristic gum found in the vessels 

 of diseased cane. He also noted the resistance of variety to the disease. 



Erwin Smith thus describes the appearance of the organism: 



The organism appears as an actively motile, short rod, and when stained 

 and imbedded in balsam has an average measurement of 0*4 : 1 micromilli- 

 metres. Carbol violet followed by dilute alcohol produces the best films ; 

 fuchsin stains the gum, which usually adheres more or less to the cells ; the 

 "blues stain but feebly. By using the night-blue method with the scanty 

 growth obtained on ordinary agar the flagella can be easily stained. They are 

 single and terminal. The bacteria are not coloured by the Gram method of 

 staining. Spores were not obtained and are probably never formed. 



144 



