COBB S DISEASE OF SUGAR-CANE. 



In a second brief communication (an excerpt from a letter to Hallier), after speaking 

 of the discovery of a cryptococcus (yeast) in the juice freshly squeezed from diseased cane, 

 Driinert goes on to say: "In the same juice there are, however, in much greater numbers, 

 that little cell (fig. 58, a), probably the same that you name Micrococcus." A little farther 

 on we have the following confirmatory sentence: "From such cane the yellow material was 

 collected which, dissolved in water, appears as a micrococcus." He then goes on to state 

 as facts what in the light of our present more exact knowledge we know to be only infer- 

 ences drawn from inexact observation, to-wit, how these micrococci in 24 hours grow out 

 into those algal threads he has already described and figured. 



Renewed attention was called to this disease in 1893 by Dr. N. A. Cobb, who found 

 it present to an alarming extent in eastern Australia. 



Dr. Cobb observed this disease in the Richmond River district and the Clarence River 

 district in New South Wales (S. lat. 29 to 30). He has also seen gummed cane from one 

 district in Queensland and says: "It is altogether improbable that it is confined to a small 

 district in Australia." The chief complaint had been from the Clarence River region: 

 "There is scarcely a farm on the lower Clarence where gumming is 

 not abundant, and on many of them its ravages are only too apparent." 

 As to the earliest appearance of the disease we have the following: 



A fanner on the Lower Clarence told me that he saw gummed cane sixteen 

 years ago [1876] on his farm; I have no doubt of it. The disease is probably 

 nothing new; in fact, is very likely as old as the sugar-cane plant itself. I 

 think it very likely that the disease occurs wherever cane is grown. 



Tryon, in Queensland, also found a number of persons who remem- 

 bered having seen the disease earlier, one man as early as 1884, to a 

 slight extent in Rappoe cane. 



The signs of this disease observed by Cobb in Australia are best 

 stated in the author's own words: 



When a cane crop is gummed it presents a variety of symptoms that 

 vary according to the severity of the disease. When only slightly gummed 

 the crop appears to be in a fair condition. Here and there, however, will 

 be seen stools containing one or more stalks with dead tops. The base of the 

 arrow [terminal shoot or flower-stalk] in such cases will be found to be rotten, 

 and usually one or more cavities of considerable size are to be seen near the top 

 of the stalk, filled, or partially filled, with offensive matter. At first one is 

 inclined to attribute these cavities to the inroads of grubs or borers. This 

 idea is soon seen to be mistaken, for there is no entrance or outlet to the 

 cavity, nor are there any traces of excrement, both which facts prove conclusively that the cause 

 lies in some other direction. The tissue about these cavities is generally brown, black, or dark red 

 in color, and reeking with a slimy offensive substance which varies from nearly colorless, through 

 yellow, to brown. Plants whose tops have died from gumming often shoot from buds half way 

 down, but this symptom is not peculiar to gumming. It occurs also in plants nipped by frost or 

 by borers. 



If a stock which has died at the top in the manner described be cut into pieces with a very sharp 

 knife, in such a manner as to leave the cut surface quite smooth, a honey-colored gummy matter 

 will, in a few minutes, be seen to ooze slowly out and form in droplets on the end of the cut libers 

 [see fig. ij. This gum is sometimes nearly transparent, sometimes rather opaque, and varies also in 

 color from nearly colorless into various tints of yellow according to the stage reached by the disease. 

 This gummy matter is usually more abundant near the top of the stalk than near the bottom, or at 

 least oozes out more freely. In the course of an hour or thereabouts these droplets of gum become 

 so large as to run together and form large drops, and if two or three dozen cuttings from badly 

 diseased stalks be laid in a closely covered box over night one may in the morning collect from their 

 ends a teaspoonful of yellow mucilaginous gum. 



Fi. I.* 



*Fio. i. Oozing of Bacterium rascularum in drops from cut surface of diseased Australian sugar-cane. After Cobb. 



