RESEARCH IN PHYTOPATHOLOGY 203 



contents ensues. Examples of this type are found, as we 

 have seen, in the wilting of various Cucurbitaceae traced to 

 B. tracheiphilus ; in the bacterial disease of the tomato, egg-plant 

 and Irish potato; the Yellow Rot of hyacinths; the Bacteriosis 

 of Dactylis glonierafa, etc. In this category must also be in- 

 cluded the Brown or Black Rot so prevalent in species of 

 the genus Brassica and other Cruciferae. A striking symptom 

 of this disease is the blocking of the lumen of the wood-vessels 

 and also the neighbouring intercellular spaces with a kind of 

 gum or mucilage. This gum is scarcely soluble. It stains red 

 with phloroglucin and reacts to thallin sulphate but remains 

 uncoloured under the phenol-potassium-chlorate hydrochloric 

 acid test, thus bringing it within the vanillin group. It is 

 a substance probably derived from the soluble carbohydrates. 



There are many " gum-diseases," such as the Gummosis of 

 the beetroot, sugar-cane and vine, and the Gummy Flux of 

 the Amygdaleae and other trees, which have now been traced 

 to the activity of certain definite bacteria. In the " Gommose 

 bacillaire " of the vine, Prillieux shows that the alteration of the 

 tissues of the wood, which is at once recognised by the black 

 dots, consists in a production of gummy matter in the interior 

 of the wood. All the elements, the vessels and above all the 

 ligneous cells of the parenchyma become filled with a brown 

 matter of a gummy appearance in which are found quantities of 

 bacteria. An early paper by Cobb (1893) gives an interesting 

 description of the gum-disease of the sugar-cane in New South 

 Wales, the chief features of which are a dwarfing of the canes 

 and rot of the growing point, accompanied with an accumulation 

 of yellow slime or gum which, when the stem is cut, oozes out 

 in a gummy mass from the vascular bundles. Cobb ascribed 

 this disease to bacteria and named the species Baderinm 

 vasculaniui, but he did not succeed in obtaining any definite 

 results from his infection experiments. On the contrary, 

 R. Greig Smith, and in a later investigation E. F. Smith also, 

 proved by inoculations with pure cultures of the bacteria that 

 they were undoubtedly the primary cause of the infection. The 

 organism is named by E. F. Smith Psciidomonas vasculanini. 



This last example affords but another illustration of the 

 history of bacteriology in relation to plants, which has shown 

 that more complete investigations have generally served to 

 establish the pathogenicity of doubtful cases, and one is led 



