70 Bacterial Diseases of Plants 



may originate in the stign^a, this becomes cliscok)ured and the disease 

 rapidly passes down the style to the ovary. Attacked blossoms showing 

 very little obvious sign of disease may remain attached to the fruit spur 

 for some considerable time and only fall when the tree is shaken by wind 

 or otherwise, the slightest shaking being sufHcient to bring down a shower 

 of blossoms in all stages of development. After the fall of the flowers of a 

 truss the spur may remain as a barren stump or may die back, this latter 

 being in all probability due to subsequent attack by fungi such as Nectria 

 ditissima or Sclerofinia friictigena since inoculation experiments with the 

 causal organism on woody branches showed only slight damage. The 

 organism may remain viable over the winter in the tissues of the spur 

 left standing on the branch and thus may carry the disease over to the 

 following spring. 



The parasite. The causal organism is a medium sized rod with 

 rounded ends motile by 2-5 polar flagella with lophotrichous arrange- 

 ment. It stains well with the usual stains and is Gram positive. The 

 cultural and physiological have been investigated by the above named 

 authors and amplified by Miss E. M. Doidge(i2) who obtained a culture 

 of their organism from Prof. Barker in order to make comparison of this 

 organism with one isolated by her from diseased pear blossoms in South 

 Africa. Miss Doidge found certain marked differences between the two 

 organisms which seem to justify the founding of two separate species, 

 but, in view of the work of Morse (3i), which showed that quite as marked 

 differences may disappear when two organisms are "trained" on the 

 same media for some considerable time, it would seem desirable that 

 treatment on the same lines should be applied to these two strains pro- 

 ducing Blossom Blight before arriving at a definite separation. Miss 

 Doidge's paper does not make it clear whether any previous training had 

 been submitted to the two organisms before the parallel series of cultures 

 was made. 



Host j)lants. Barker and Grove found all the varieties of pear grown 

 at the Long Ashton Research Station were susceptible to the disease, but 

 that some were much more so than others; Beurre d'Amanlis and Catillac 

 being specially susceptible. The bacillus has also been isolated from 

 certain varieties of apples, plums and cherries. Barker (4) has also 

 isolated an organism from gooseberry bushes which is believed to be 

 identical with the organism causing pear blossom blight though no 

 cultural evidence of this has as yet been given. 



Distribution. The organism has been isolated from affected flowers 

 from rjloncestershire, Devon, Middlesex, Sussex, Essex, Staffordshire and 



