94 Disease of Fruit Blossom 



on the disease, the available e^'idence indicates that the disease is 

 encouraged by a comparatively low temperature and a damp atmo- 

 sphere and conversely is checked by hot and dry weather. The conditions 

 within the bags approximate to the latter type. 



Since it was discovered that the tissues of the fruit spurs of pears 

 were frequently attacked by the organism several infections were made 

 in young shoots of apples, pears, plums, and gooseberries, by means of 

 needle punctures. Control punctures with a similar sterile needle were 

 made at the same time. The two sets of shoots were compared at 

 monthly intervals, and it was found that, although the inoculated punc- 

 tures were full of the living bacteria, so much as to show that some 

 multiplication had taken place, the organisms had not spread appreciably 

 in the tissues nor caused more than a minimal amount of local damage. 

 Macroscopically the infected shoots differed in no way from the controls. 



A few infections on Catillac pear fruits when they had nearly attained 

 their maximum size were also made by puncture. No serious results 

 ensued. 



Isolation, Description, and Cultural Characters of the Bacillus. 



As already mentioned, microscopical examination of the tissues of 

 the discoloured areas of the flowers, leaves, and fruit spurs showed them 

 to be swarming with cells of a rod-like bacterium. The detection of 

 the organism was generally difficult and frequently impossible when 

 material for examination was selected from the centre of the blackened 

 patches owing to the alterations in the diseased cells of the tissues. 

 The formation of granular substances and the abundance of compara- 

 tively opaque and darkened cell contents prevented satisfactory identi- 

 fication of the presence of the parasite. It is indeed probable that the 

 latter dies off in those places. When, however, portions of the tissues 

 at the periphery of the discoloured spots bordering on healthy unattacked 

 cells were examined, there was generally no difficulty in finding the 

 bacteria in abundance and in a most active condition. There appears 

 to be a zone of the bacteria along the periphery of the affected areas, 

 where fresh cells are being attacked, which advances with the spread 

 of the discolouration ; while behind, where the cells of the host have been 

 killed, the parasite has migrated or died off. 



The isolation of the organism from the peripheral portions of affected 

 areas was simple. Plate cultures of malt extract gelatine infected from 

 such regions gave colonies of the bacterium in the course of four or five 

 days. Many independent series of plate cultures have been made from 



