6 BACTERIA IN RELATION TO PLANT DISEASES. 



The gum which thus oozes out in such quantities, if allowed to do so, at last becomes dry, owing 

 to the evaporation of its water. In this state it appears as bright yellow stains on the end of the 

 cutting. Sometimes the gum oozes out in a state so nearly dry that it hardens as it issues from the 

 fibers into a yellow, coiled-up, hair-like body, and inasmuch as each fiber gives rise to one such body, 

 all the fibers together originate a yellow, mossy appearance on the end of the cutting. 



If another stalk, which is apparently sound, be taken from a stool in which one or more stalks 

 have been already blighted by gumming, as above described, such stock will be found to exhibit the 

 same symptoms, except that the cavities and rottenness at the base of the arrow are wanting. More- 

 over, if other stalks be removed from shoots of cane standing nearby in the same field, but which, 

 as yet, show no outward symptoms of this disease, the chances are that some of them will also be 

 found to be more or less gummed. 



In some cases the amount of gum is so small as to ooze out in but a trifling quantity, to be 

 detected only with a magnifying glass. Finally, the quantity of gum may be so small as not to 

 ooze out at all ; in such cases a good microscope is necessary to demonstrate that the gum is present. 



"Gumming" is considered by Dr. Cobb to be a good descriptive term for this disease, 

 although he states that the substance is not a true gum. I continue to quote from Dr. 

 Cobb's paper: 



After the cane is cut and ready for the mill, gummed stalks can be recognized not only by the 

 yellow dried-up gum that exists on the cut ends, but also by their color. Gummed stalks generally 

 have an over-ripe appearance. Green and yellow canes, when badly gummed become yellowish or 

 orange, or even somewhat purple in color. The ribbon canes show similar alterations in their yellow 

 stripes while their purple or black stripes tend to take on a reddish cast. The waxy bloom, usually 



to be seen on perfectly sound cane, has disappeared on 

 badly gummed cane. All symptoms of gumming seem to 

 be more pronounced when they occur in plant cane than 

 when they occur in ratoons.* An explanation of this fact 

 will be offered later on. 



In the sugar mill the juice of gummed cane may be 

 recognized by the greater amount of lime required for its 

 clarification, and there seems to be reason to suppose that 

 Fig. 2.f the crystallization of the jellies is slower and less perfect 



when they are derived from gummed cane. The sieves 



used to separate the fiber from the juice are apt to clog up when gummed cane is being crushed. 

 They are easily cleaned with soda. 



The foregoing symptoms are those connected with cane so attacked as to produce a marketable 

 crop. In some cases, however, the gumming prevents the growth of the sets. The plants may reach 

 a height of a foot or two feet, but they then die back and shoot again from the base, or from buds 

 half-way down the stalk. In such a case the loss is total or nearly so. The gum presents the same 

 features in this case as in milder ones. 



So much for the gross appearance of this disease. A microscopic examination gave 

 the following additional facts, which seem to have been made out very satisfactorily: 



A microscopic examination of a thin slice across a gummed cane shows at once that the disease 

 is not general, but local. The gum, except in certain cases, is confined to the fibers; in fact, to the 

 sap-vessels, these latter being plugged up with gum. A cross-section of a healthy fiber shows the 

 sap-vessels as empty spaces, the sap having flowed out [?] in the process of cutting the section; a 

 cross-section of a gummed cane on the other hand shows the sap-vessels to be filled with yellow 

 granular matter, in other words, gum. This confinement of the gum to the sap-vessels is one of the 

 most striking microscopic features of gummed cane. In advanced cases, and in the more tender 

 tissues at the top of the cane, the gum is not so local in its distribution; it may, under such circum- 

 stances, be found outside the fiber. 



*Plant-cane is the first year's crop from buried cane or cane cuttings. Ratoon-cane is the second crop from a 

 stool or any subsequent crop. In the rich cane-lands of Australia sometimes as many as 10 or 15 successive crops are 

 obtained without renewal of the root-system. In Cuba it is customary to plant some cane annually, but ratoon 

 crops are also common. 



fFlG. 2. a, Bacterium vascularum from sugar-cane stained with methyl violet without heat, and mounted in 

 water; b, Bact. vascularum from a culture on cane-sugar agar; c, Bact. vascularum from sugar-cane, stained with 

 fuchsin and mounted in balsam. Xz,7oo. After Cobb. 



