190 SUidies in Bacteriosis 



become swollen and browned, and the middle lamella is destroyed, thus 

 opening up a passage for the organism (see Fig. 4). The wood parenchyma 

 is distorted and browned and occasionally the wood vessels themselves 

 are attacked and their walls disintegrated. Once through the vascular 

 region the organism readily finds its way through the cortex to the ex- 

 terior where it spreads upwards in the outer cortical layers and epidermis; 

 the affected cortical cells collapse and the characteristic depressed stripe 

 is thus produced on the surface of the stem. Anatomical examination 

 of artificially infected plants has fully confirmed the conclusions drawn 

 from naturally infected stems. 



ISOLATION OF THE CAUSAL ORGANISMS 



The organism was first isolated in September, 1918, from plants 

 grown under glass without artificial heat. The plants were badly attacked 

 when first observed and the crop of that house was an entire failure. 

 Sections of the stems showed no sign of active bacteria and several 

 attempts to isolate the organism from the stem proved abortive. In one 

 instance out of perhaps twenty attempts a yellow organism in company 

 with others was obtained on plating from the diseased pith and this 

 afterwards proved identical with an organism which was much more 

 readily obtained from diseased patches on the fruits. Many of these 

 fruit spots seemed to be sterile and frequently on incubation of a dis- 

 eased fruit the disease failed to extend further. It must be concluded 

 that the organism which had given rise to these diseased patches was no 

 longer viable. A similar case of the disappearance of a plant parasite in 

 diseased tissue has been briefly described in the disease named by one 

 of us (Paine (5)), the Internal Disease of the Potato, and has been sus- 

 pected by the same author in a Leaf Spot Disease of Profea(6). It is 

 quite probable that bacteriolysis in plant tissues is a more common 

 phenomenon than it is at present believed to be. This may account for 

 the fact that Howitt and Stone (2) and the four well-known bacteriologists 

 to whom they submitted diseased plants failed to isolate any causal 

 organism from tomatoes bearing exactly the same symptoms as are 

 associated with our "Stripe." 



The organism can often be seen in the intercellular spaces of sections 

 of diseased tissue from a fruit spot, and platings made from such tissue 



• The joint authors of tliis paper isolated the same organism independently and finding 

 they were studying the same disease agreed to collaborate. The cultural work has been 

 carried out by the first-named author at the Imperial College, while the other is responsible 

 for the inoculation experiments which have been conducted at Cheshunt. 



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