12 BACTERIA IN RELATION TO PLANT DISEASES. 



As an illustration of a still further advance in the progress of the malady, a plant may exhibit 

 the following symptoms: The central shoot and leaves are already quite dead, though still flaccid, 

 and readily yield to a slight pull. There occurs also in those, on either side of it, that are still partly 

 green, a brown band of dead tissue, proceeding along each margin; this band widens in the case of 

 the outer leaves, whilst the outermost of all are all involved in it, being quite dead. The cane itself, 

 instead of exhibiting that yellowish colour indicative of the fact that it is already ripe, is of a dull 

 bright-green colour above; nearer the ground it is clouded, with the same hue, but at the extreme 

 base evinces little unusual in this respect. All the buds except those situate lowest on the cane have 

 sprouted, some having given rise to peculiar elongated slender shoots ; beneath the leaf -sheaths the 

 buds are already dead or apparently dying. * * * On cutting any of these canes across, small 

 bright droplets of a canary-yellow thick adhesive substance will arise from the pores distributed over 

 the surface of the section, and in many instances will run together and coalesce. When the disease 

 is advanced to the stage above described, some of the buds within an inch or so of the decaying 

 summit of the shoot may shoot out and develop a tuft of narrow leaves; but no further growth 

 takes place in the cane itself, though the latter may be some time before it actually dies. * * * 



All the canes that arise from a single stool may not be affected simultaneously and to an equal 

 extent. As an instance of this, the following occurrences were remarked in the case of an affected 

 plant : All the canes had been checked by cold when they had experienced from six to seven months' 

 growth, otherwise the plant was remarkably robust. Three of them had the central shoot, and 

 several of the lateral ones already dead. A fourth had the leaves as well as the central shoot quite 

 green, and all of these canes exuded droplets of gummy substance when their stems were cut across. 

 A fifth cane the stoutest of all was entirely wanting in the gummy exudate, as was seen when 

 after lopping off its top and allowing it to remain still connected with the ground, none of this gum 

 was observable even after the lapse of some hours. In addition to these five canes, there were several 

 suckers, some of which had formed cane, and were almost as high as the stalks that surrounded them. 

 These, however, even when arising alongside gummy canes, were themselves apparently quite free 

 from disease, as no "gum" emanated from their cut ends. 



In October 1895, in the Agricultural Gazette of New South Wales, Dr. Cobb reported 

 on his inoculation experiments. The cane-disease was produced, apparently at least, by 

 means of his Bacillus vascularum, but the inoculations were too few to be very conclusive, 

 because they were made in a region much subject to this disease and also because not 

 enough plants were held as checks. 



Under the circumstances, i, e., much diseased cane in the vicinity, not less than 100 

 canes should have been inoculated and as many more held as checks. Cultures derived 

 from single colonies should also have been used for purposes of infection rather than ooze 

 from diseased canes, although the author quite agrees with Cobb that the organism often 

 occurs in practically pure culture in the interior of the diseased canes. 



The reader will be able to judge of the quality of the evidence by reading the following, 

 from Dr. Cobb's report, which contains all that is pertinent: 



Six inoculations were made, one a check that is, pricked with a sterilized needle only. The 

 stools were in charge of Mr. C. N. Stevens, Manager of the Colonial Sugar Refining Company's mill 

 at Harwood. At the time of inoculation all the stools appeared to be healthy. 



The canes [which were inoculated in August 1893] were forwarded to me at Sydney in September, 

 1894, and examined with the following result: 



i. Mr. Stevens reported the check lost. 2. Of the inoculated canes, four were still alive, the 

 other was dead. 



All the four living canes were gummed one slightly, but very manifestly ; two very markedly ; 

 the fourth dying, and evidently from gum, though fungi had made their appearance. The gumming 

 was most marked in the neighborhood of the point of inoculation and above it, though it appeared 

 throughout the culm. 



Concerning the dead and dying canes, Mr. Stevens writes: "The dead canes have probably 

 some time or other been broken off or shaken at the root, which would account for their demise." 

 The fact that one of the still living stalks, as reported above, was dying, and to all appearances from 

 gumming, would suggest that death may have been caused by gumming. It is impossible to say, 

 however, from the dead and dying canes in their present dry condition, what was the cause of death. 

 The canes were in five different stools. Mr. Stevens writes: "All the canes in those stools are now 



