602 TRANSACTIONS OF SUB-SECTION K. 



dispersion of the invading bacilli. Further, certain bacteria have the power of 

 secreting a toxin and cytolitic enzyme which effect the destruction of the proto- 

 plasm and rapid degeneration of cellulose, and the actual penetration of the 

 bacterium through the cell-wall has been observed. A complete homology has 

 been established between the parasitism of bacteria and that of various parasitic 

 fungi. In the same manner as fungi, bacteria also exist as saprophytes, which 

 have the faculty, under certain conditions, of developing into virulent parasites, 

 and their aptitude as parasites may be increased or suppressed upon subjection 

 to variations of nutrition. 



There are various well-marked types of bacterial disease which differ con- 

 siderably in their pathological character and in the extent of the injury which 

 is produced. Some are characterised by rapid proliferation of the cells, forming 

 galls or tumour-like structures ; in some the bacilli are confined to the vascular 

 tissue, in others their action extends through the parenchyma ; and in many cases, 

 such as the ' Soft Eots,' spreads throughout the entire cell-complex until the 

 whole plant becomes reduced to a putrefying mass. The organisms which are 

 pathogenic to cultivated plants are more particularly considered, and the different 

 external conditions which influence the susceptibility to disease. The nature of 

 the soil, manurial treatment, and other factors materially affect the constitution 

 of both host and parasite, and determine to a large extent the predisposition to 

 infection by bacteria. 



(ii) Bacterial Gum Diseases. By F. T. Brooks, M.A. 



1. Gum Disease of the Sugar-Cane. — In 1893 Cobb described a ' gum disease ' 

 of the sugar-cane in Australia, one of the chief features of the disease being the 

 presence of a gummy substance in the vascular bundles of the stem. Cobb attri- 

 buted the disease to the action of a bacterium which he named Bacillus 

 vasculartim. He performed certain inoculation experiments, but as they were 

 not carried out under critical conditions the results were generally considered to 

 be inconclusive. 



In 1904 Erwin F. Smith, 1 working in America, proved conclusively that the 

 disease was caused by a specific bacterium which he named Pseudomonas 

 vascularum. This organism was plated out from diseased canes and grown in 

 pure culture. Inoculations with the bacterium cultivated in this manner gave 

 rise to the characteristic signs of the disease. The same bacterium was plated 

 out from the inoculated canes. 



2. A Bacterial Disease of Cherry Trees. — Aderhold and Ruhland 2 have 

 recently proved that a disease of cherry trees in Germany is caused by a 

 bacterium which they name Bacillus sponaiosus, Affected trees exhibit symptoms 

 similar to those of pear trees attacked by 'pear blight,' which is also a bacterial 

 disease. Young trees are attacked, 6hoots and entire trees being sometimes killed. 

 Profuse gumming occurs in the affected parts. Aderhold and Ruhland isolated 

 Bacillus spongiosum from the masses of gum and grew this organism in pure 

 culture. Inoculation experiments clearly showed that this bacterium was the 

 cause of the disease. This organism is not the only cause of gumming, for 

 certain injurious fungi are known to induce similar exudations from cherry trees. 



3. Mosaic Disease of the Tobacco Plant. — This disease is present in almost 

 every region where tobacco is cultivated. Mayer 3 and Iwanowski * formerly 

 attributed it to bacterial agency, but more recent work by Hunger s and others 

 points rather to the conclusion that the disease is not due to any specific organism 

 but to some physiological disturbance within the plant. 



(iii) Bacterial Diseases of the Potato-plant in Ireland. 

 By Dr. G. W. Pethybridge. 



The presence of bacterial disease among potatoes in Ireland has been sus- 

 pected for some considerable time, but no definite proof of the existence of such 

 disease has hitherto been forthcoming. As a result of a couple of seasons' study 

 carried on in the West of Ireland at a temporary research station established by 



1 Cent. f. Bahteriologie, 1904. 2 Ber. d. Dent. Bol. Qes., 1906. 



8 Landwirt. Versvch'tat., 1880. * Ze'.t. f. Pfar-enkranl:, 1903. 5 Ibid., 1905. 



