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A bactp:rial disease of fruit blossom. 



By B. T. p. barker, M.A. and OTTO GROVE. 

 {University of Bristol : Agricultural and Horticultural Research Station.) 



In the Gardeners'' Chronicle of May last year an announcement was 

 made by one of us that several cases of blackening of pear blossoms, 

 commonly supposed to be due to frosts or cold winds, had been traced 

 to the action of a bacterium. For several seasons past the blackening 

 of the blossom followed by the death of the flower has been observed 

 in the plantations of this institution at Long Ashton, the severity 

 of the attack varying from year to year, but on the whole showing a 

 tendency to increase. In the spring of 1913 the disease was much more 

 marked than at any time previously ; and although the trees of most of 

 the varieties grown there were heavily laden with blossom, the crop was 

 a failure, certain varieties being especially severely attacked and failing 

 to produce more than half a dozen or so mature fruits per tree on good 

 sized trees ten or twelve years old. Until then no particular attention 

 had been given to the disease, the damage being attributed to the action 

 of frost and cold winds according to the generally accepted view. Mr 

 J. W. Eves, at that time pomologist at this station, observed during the 

 course of polhnation work on pears early last April that in many in- 

 stances the pistils of unopened flowers were already badly discoloured, 

 and was impressed with the general resemblance of the features of the 

 disease to an attack by a parasitic organism rather than to damage 

 caused by unfavourable weather conditions. He accordingly submitted 

 to us typical diseased blossoms for examination, selecting cases where 

 frost could not possibly be held responsible for the damage. In the 

 case of the first flower examined a large semi-transparent gelatinous- 

 looking colony of bacteria was readily seen under the low power of the 

 microscope situated on the surface of the discoloured disc of the flower. 

 From this colony streak and plate cultures on beerwort gelatine were 

 at once made, and in these in the course of two or three days abundant 

 growth was obtained. The cultures in all cases proved to be pure, only 



