B. T. W Hai{kkk AM) (). (;k«)VK 93 



details. It was found that although infection was obtained by both 

 methods, the disease set in much more readily when the tissues were 

 punctured. By the latter method the flowers formed small moist drops 

 in three to four days after infection at most of the injured spots, and on 

 the fifth day distinctly grey coloured slimy colonies could be seen. After 

 six to seven days the affected areas were black and exactly like the 

 natural ones. Microscopical examination of the tissues of these regions 

 showed a heavy growth of the organism, and the latter after isolation 

 in pure culture again presented all the characters of the original type. 

 It is noteworthy that in practically every case tested the bacillus in 

 question was the only one isolated from the affected tissues. In due 

 course the blackening spread to other parts of the flower in the manner 

 already described in connection with the disease under natural conditions. 

 Control experiments in which the flowers were punctured with a sterile 

 needle, but not inoculated with the organism, gave in the large majority 

 of cases negative results. Some discolouration occurred at the point 

 of injury, but nothing further resulted. Where the control experiments 

 in a few cases showed a development of the disease at such points, it 

 is probable that the organism was already present on the flower at the 

 time of injury. There is evidence to show that the bacillus is at times 

 present on the surface of perfectly healthy flowers. 



The infection experiments in which the tissues of the flowers were 

 uninjured yielded less striking results, although in the great majority 

 of cases the disease eventually developed. 



Owing to the extent of the disease on the trees at Long Ashton last 

 spring, the selection of unaffected blossom trusses for infection experi- 

 ments was difficult. Many instances of the disease developing without 

 artificial infection on selected trusses apparently quite healthy occurred ; 

 and although there is no question of the success of the infection experi- 

 ments, there were occasions when it was difficult to decide as to natural 

 infection also playing a part. 



Infection experiments were also made on flowers on trees growing 

 in the open plantations at this institution. These were less satisfactory 

 than those already recorded. In the first place it was almost impossible 

 to distinguish between the results of artificial and natural infection, 

 the latter being so common, when the infected trusses were not enclosed 

 in paper bags ; and secondly, when paper bags were used, a large number 

 of artificially infected trusses remained healthy, the controls behaving 

 similarly. Probably this was due to the effect of bagging on the flowers. 

 While at present we know little as to the influence of external conditions 



