Studies on the Fire-Blight Organism, Bacillus amylovorus 37 



1, 2, 3, and 4 inches, respectively, two plants again being used for 

 each distance. This procedure was continued for seven or eight days, 

 at the distances indicated in table 6. Eight days later the plants were 

 inspected, to determine from which ones the blight had been removed and 

 those in which infection had progressed beyond the point of cutting. 

 If killing had progressed after cutting, it was assumed that the fire- 

 blight pathogene had passed that point before the cut was made. If 

 no further killing had occurred, it was assumed that ail bacteria were 

 removed when the twig was severed. That fire-blight bacteria will not 

 migrate at the same rate in all shoots is to be expected, but some cor- 

 relation in the rate at which invasion progresses is shown in table 6. 

 It appears that immediately after inoculation, some time is required 

 for the marshaling of the bacterial forces before their invasion of 

 new tissue. After migration has begun, the rate is fairly uniform for 

 the first seven days, for the three series. Variations exist in the indi- 

 vidual series, which may be due to changes in atmospheric temperature 

 or in relative humidity, or to variation in the growth processes of each 

 host plant. 



EPIPHYTOLOGY 



DISSEMINATION OF THE ORGANISM 



Both Burrill (1881b) and Arthur (1885 a, 1886) speculated on the 

 mode of spread of the fire-blight bacteria. Arthur (1885 a) expressed 

 the opinion that the bacteria, after being washed about, dried up, were 

 then blown about by the wind, and, alighting on the "delicate surface 

 tissues of expanding buds, or the exposed internal tissues of fresh 

 cracks or wounds." caused the disease to develop. He noted a progres- 

 sion of blight from the direction of the prevailing wind. He was "not 

 inclined to consider" insect transmission as a "very frequent means of 

 contagion." Waite contributed the first experimental evidence on 

 insect transmission in 1898, although three years earlier he had stated 

 that bees, wasps, and flies are attracted to the exuding bacterial ooze 

 and undoubtedly carry the microbe to the opening blossom. 



The role of bees in dissemination was more recently investigated by 

 Gossard and Walton (1922), who found that Bacillus amylovorus can 

 live in honey for seventy-two hours or more, and who were able to 

 produce killing of apple shoots, attributed to fire blight, by inserting 

 the mouth parts of bees into such shoots during blossoming time. That 

 many species of insects may transmit fire blight can hardly be ques- 

 tioned when one reads, in addition to the references mentioned, the 

 reports of D. H. Jones (1909), Whetzel and Stewart (1909), O'Gara 

 (1908, 1910), Stewart (1913), Stewarl and Leonard (1916), Smith 

 (1920), and Brooks (1926). That the blight organism may be trans- 



