COBB S DISEASE OF SUGAR-CANE- 13 



more or less gummed." The question arises: Would these five canes have become diseased if they 

 had not been inoculated? As stated above they appeared at the time of inoculation to be perfectly 

 healthy, and this, of course, was the reason why they were chosen for the experiment. This fact 

 their apparent healthiness is in favor of their remaining healthy. The gumming in the canes for- 

 warded to me was most marked near the point of inoculation and above it. This fact is in favor of 

 the disease originating from the inoculation. As reported below, canes were also inoculated with a 

 fungus. In the same stool two stalks were inoculated with microbes. In the case of this stool the 

 two stalks inoculated with the fungus showed no trace of gumming, though they were examined 

 minutely. * * * This fact is again strongly in favor of the gumming which appeared in this stool 

 having originated from the [bacterial] inoculation. 



Against these facts and deductions must be set the fact that a large part of the cane on the Lower 

 Clarence, where these experiments were made, suffers from gumming. I think it may fairly be said 

 that the canes taken for experiment were not very liable to become gummed, as they were in good 

 garden soil not before under cane, and had good care and were derived from what were supposed to 

 be sound crops. 



To the writer the strongest evidence adduced by Cobb is that the gumming was most 

 pronounced in the vicinity of the inoculations and upward therefrom. I might also add 

 that after seeing gummed cane and examining the yellow ooze microscopically, I became 

 at once less skeptical, and am now [this paragraph was written in 1902] strongly inclined 

 to believe that Dr. Cobb is correct in his conclusion as to the cause of this disease, although 

 his inoculation experiments are not entirely conclusive. 



At the close of this paper, which is largely a repetition of statements made in the 

 previous one, Dr. Cobb says that as a result of his former publication it has been shown 

 that cane in Java, New Guinea, Brazil, Mauritius, etc., either suffers now or has in the 

 past suffered from what is beyond reasonable doubt the same disease gumming. 



In 1902, R. Greig Smith published, in Australia, a paper on "Gummosis" of the sugar- 

 cane. He isolated the organism and described its growth on various culture-media, but 

 said nothing of any inoculations. His studies were mostly on the nature and origin of the 

 gum and were carried on along the lines of qualitative chemistry. Through the reactions 

 of the gum, which were for the most part the same as those of the bacterial slime obtained 

 from pure cultures on agar, he came to the conclusion that the two were identical and 

 consequently that the gum in the diseased canes was of bacterial origin and not a patho- 

 genic secretion of the plant upon which the bacteria lived saprophytically. The following 

 paragraph is quoted from his paper : 



When a pure culture of the bacterium is smeared over the surface of neutral cane-gelatin or agar 

 in a suitable vessel and incubated, a luxuriant growth is obtained after the lapse of about a week. 

 The culture is precisely similar in appearance and consistency to cane-gum. Both have the same 

 soft buttery appearance and gummy consistency and both slowly mix with water to form a pale 

 yellow opalescent solution. The opalescence is due to the suspended bacteria, from which [solution] 

 it is rather difficult to separate [them] without at the same time removing the gum. The separation 

 can not be effected by filtering through paper, and the usual coagulating agents coagulate both gum 

 and bacteria. Aluminum hydrate, for example, forms an insoluble compound with the gum. An 

 attempt was made to clarify the suspension by heating it up to three atmospheres in the autoclave, 

 a proceeding which was successful with another gum-forming bacterium, but the suspension was 

 unaltered. Eventually the bacteria were separated by filtration through porous porcelain. A clear 

 solution of the gum was thus obtained, but at the same time it was noted that a considerable amount 

 of the gum remained on the porcelain, adhering to the bacteria, even after the suspension had been 

 boiled for some time to diffuse the gum. The filtered and clear solution was tested simultaneously 

 with an opalescent suspension, and it was found that the two behaved similarly to the addition of 

 the various reagents, from which we must conclude that in the suspension the bacteria are inert, and 

 for purposes of identification of the gum it is unnecessary to separate them. 



He gives the following table (table 3), showing the chemical reactions of the gum 

 taken from cane and of the bacterial slime formed in laboratory cultures: 



