H. ^r. 1*. HaiuvKR and O. OiK.vK 89 



of the disease the following spring through the lateral biuls which were 

 formed after the original attack. On cutting transverse sections through 

 such a spur just below the point of attachment of the diseased 

 flower truss a number of small brown spots are seen, both inside 

 and outside the cambium. In longitudinal section these appear as 

 brown lines, which at times extend back i-1 inch or more into the woody 

 portion of the spur. The bacillus is present in these affected portions ; 

 and proof is now^ forthcoming that it remains in a living condition there 

 over the winter. It seems likel}^ therefore, that new growths from such 

 spurs are also infected. The affected portions of the tissues of the spurs 

 do not increase in size to any considerable extent ; and no serious damage 

 to the surrounding tissues results immediately, except in the severe 

 cases where the whole body of the spur dies back. Possibly in the latter 

 event the death of the spur may be due not so much to the organism 

 in question as to fungi, such as Nectria ditissima or Sderoliniafructigena 

 which have the opportunity of infecting the spur at the point of 

 severance of the blossom truss. At present no decisive evidence either 

 way has been obtained ; but, as will be seen later, infection experiments 

 with the bacillus on woody branches have shown little serious damage, 

 and the balance of probability therefore points to the action of other 

 organisms in cases where the spur dies back. 



In the foregoing description of the disease reference has been confined 

 to its characters on the pear as host. There is reason to believe, however, 

 that a number of other plants are also susceptible to attack. A bacterio- 

 logical examination of discoloured parts of flowers of apples, cherries, 

 gooseberries, and plums has been made, and in many cases there has been 

 found in the diseased areas a bacillus in practically a pure state, which 

 on isolation has proved to be the same organism as that occurring on 

 the diseased pear flowers. It has also been found on the tissues of the 

 flowers and leaves of various other plants in parts showing discolouration. 

 Since at present, owing to our attention having been given mainly to 

 the disease on the pear, very few infection experiments have yet been 

 made on the other plants mentioned, the evidence connecting the bacillus 

 with the disease in the latter cases is not absolutely conclusive ; and 

 pending further investigation it is not proposed here to do more than 

 call attention to the fact of the occurrence of the organism in association 

 W'ith affected parts on other kinds of plants. 



There appears to be a marked difference in the susceptibility of difi'er- 

 ent varieties of pears to attack. The organism has been isolated from 

 diseased flowers of practically all the varieties grown in the plantations 



