IO 



BACTERIA IN RELATION TO PLANT DISEASES. 



another in fields barely cleaned of the brushwood, still less of weeds, unploughed, undrained, needless 

 to say never manured, seldom weeded, the canes being never trashed, the ratoons uncared for. 

 After taking off one or two ratoon crops, the land is abandoned for a period of not less than 3 years. 

 The seed cane is frequently taken from any old abandoned piece; no selection is ever made. 



All the themes as to causes suggested by the planters and others were flatly contradicted in 

 actual practical experience ; some said, for instance, that the salt air was to blame, and the disease 

 did first make its appearance on the coast, but when it afterwards crept farther up country it should 

 have died out, which it did not. 



Some suggested exhausted soil, but the disease appeared in canes grown from uninfected sources 

 in virgin and rich soil. Others put it on degenerate seed cane, and certainly to judge from the seed 

 cane often used any imaginable disease might result, but the offspring of fine healthy cane brought 

 from far inland districts also suffered. 



The planting of pieces of cane and tops also made no difference; the former is the almost invari- 

 able custom here. 



In a wet season more cane was usually attacked than in a dry season. 



It is probable that, as has been suggested in other cases, the responsibility of its appearance 

 must be laid on a combination of causes inducing general debility and aptitude for catching disease, 

 rather than to any one particular cause. These elements of disease, if they may be so called, are 

 like malaria in a swamp, always present and only awaiting suitable subjects. 



In the absence of definite evidence as to the cause of the disease, improved methods of cultiva- 

 tion, manuring, advisedly not indiscriminately done, regeneration of stock by selection, the rearing 

 of seed-cane in nurseries, were advised. 



The method adopted, however, was more heroic; as the planters could not find a cure, they 

 threw out the Cayanna and other canes affected, and introduced varieties of foreign origin. 



The dark claret coloured cane with a still darker stripe, called here " Louzier," was the principal 

 kind introduced, also the "Lalanjore," and some 70 others. (As the names of these when first 

 received were much mixed up, it is possible that "Louzier" is not the correct name for this cane.) 



None of these new varieties had been attacked, though now growing 15 years under precisely 

 similar circumstances as regards bad methods of cultivation, and the Cayanna is again being success- 

 fully cultivated on lands which ten years ago could not grow it. As it is a far better cane as regards 

 yield and early maturity than the new ones, it is to be hoped this improved state of things will 

 continue. 



In 1894, M. Boname reported Cobb's bacterial disease of sugar-cane as common in 

 the Mauritius, especially on a variety called I/a canne Bambou. 



In the beginning there are no external signs. As the disease progresses growth ceases, 

 the head shortens, the 5 or 6 green leaves remaining at the top grow paler, bleach, become 

 yellow, and dry out. Sometimes shoots (ailerons) in greater or less abundance are pushed 

 out of the upper nodes, but more often the whole cane dries out and dies. When the leaves 

 begin to turn yellow, if the stem is cut transversely, little masses of viscid grayish yellow 

 matter appear on its cut surface and dry yellow. This gum is generally more abundant 

 toward the top of the stem. In early stages of the disease the gum is extruded only from 

 isolated points. In bad cases the gum is very abundant and the gummy foci unite to 

 form large, sticky masses covering a considerable part of the section. The gum is not 

 disseminated through all the tissues of the stem. It is seen only in the interior of the two 

 large vessels which form the center of the fibro-vascular bundle, and is not found in the 

 sugar-cells. 



Among other results, chemical analysis proved the amount of sugar to be less in diseased 

 canes than in heal thy canes grown under otherwise identical conditions, as shown in table 2. 



TABLE 2. Reduction of Sugar in Diseased Canes. 



