38 



A. L. PlERSTORFP 



mftted by the pruning knife or by other tools has been proved by 

 Whetzel (190G), Stewart (1913), and others. Pickett (1914), Gossard 

 and Walton (1922), Talbert (1925), Brooks (1926), Miller (1928), 

 Tullis (1929), and Rosen (1929) think that meteoric water plays an 

 important part in dissemination, by washing the bacteria either into 

 wounds or over blossoms and young, tender, growing shoots. Stevens 

 and others (1918) suggest support of Arthur's hypothesis of wind dis- 

 semination. Thus we find a diversity of opinion as to which agent or 

 agencies bring about the rapid dissemination of fire-blight bacteria. 

 That in different regions and in different seasons the percentage of 

 spread attributable to any one agency may vary greatly, is indicated. 



Following the announcement by Gossard and Walton (1922) in 

 Ohio that rain acts as a vector of B. amylovorus, tests were made in 

 New York to determine whether this method of dissemination might 

 be one of the contributing factors in causing epiphytotics of fire blight 

 under conditions prevailing in this State. In order to exclude insects 

 and not rain, ten coarse cheesecloth bags (22 meshes to the inch), each 

 one-half yard wide and approximately one yard long, were tied on 

 branches of Tompkins King apple trees at Ithaca on May 14, 1925. The 

 blossom clusters had just begun to unfold. After a few days, when 

 some of the blossoms in the bags and on other parts of the tree had 

 opened, approximately one hundred blossoms immediately above each 

 bag were atomized with a virulent culture of B. amylovorus. The blos- 

 soms in the bags were protected from accidental inoculation by the 

 bouillon during atomizing, since preliminary tests had shown that these 

 blossoms could be inoculated with an atomizer through the cloth. In 

 the course of a week to ten days there was a semicircle of blighted 

 blossoms above each bag. The number of blighted blossoms in the bags 

 is shown in table 7. The precipitation and temperature records during 

 these tests are given in tables 9 and 11 pages 42 and 44). 



TABLE 7. Infection in Bagged Blossoms by Bacillus amylovorus 



* These five blossoms were all in one cluster and were appressed to the cheesecloth, and could easily 

 have been inoculated by an insect through the meshes of the cheesecloth. 



