202 SCIENCE PROGRESS 



Thus the bacilli play here a part absolutely comparable to that 

 of the fungi and a complete homology is established between 

 them. 



This form of parasitism is apparently typical of a large 

 class of bacterial diseases, in which there is a rapid degeneration 

 of the cell-wall and complete destruction of the parenchymatous 

 tissues. Van Hall's researches in 1902 demonstrated the action 

 of a toxin secreted by Bacillus omnivonis when attacking Iris 

 florentina; and three years later (1905) Jones isolated a cytase 

 in the case of the soft rot of the carrot and other allied plants, 

 due to B. carotovorus. In 1906 Harrison also described the 

 action of a cytase in his investigation of a disease of cauliflowers, 

 caused by B. oleracecc, which exhibited symptoms identical with 

 those produced by P. destnictaus. Jones has since shown that 

 all these three organisms must be considered as representative 

 of one species. This author has recently published a very 

 interesting comparative study of the group of organisms pro- 

 ducing the bacterial white soft rots (1909) and he shows that 

 Bacillus carotovonis, as well as certain other soft-rot organisms, 

 excrete a cytolytic enzyme which he determines to be a 

 pectinase. In all probability a cytase is also concerned in 

 certain of the potato rots, though in these last instances it has 

 not been isolated. 



A species of Pseudomonas producing a brown rot of the 

 turnip, which I have had under investigation, belongs to a 

 group working in a totally different manner ; the action is 

 very much slower and the rapid swelling of the cell-wall is not 

 a conspicuous feature. The tumerous diseases, such as the 

 canker-knots of the olive and the Aleppo pine, caused by 

 Bacillus olece and B. pirn respectively, also exhibit a com- 

 paratively slow development. 



Another type of bacterial disease is that in which the xylem 

 vessels are primarily attacked and become filled with numerous 

 bacteria. As a consequence the transpiration current is unable 

 to flow along these channels, the supply of water is cut off and 

 hence a withering of tlie shoot occurs. In the bacterial disease 

 of sweet-corn a variety oi Zea Mais, described by F. C. Stewart, 

 the organism is confined exclusively to the fibro-vascular 

 bundles and never pervades the cells of the parenchyma. In 

 many other cases there is subsequent invasion of the paren- 

 chymatous tissues and total destruction of the cell and cell- 



