Studies on the Fire-Blight Organism, Bacillus amylovorus 47 



bacteria into blossoms is through the nectariferous surfaces. Entrance 

 through stomata or other natural openings was not found in this 

 region of the flower. That the bacteria, after multiplying in the nectar, 

 might gain entrance into the interior through the nectar-secreting 

 cells by either toxic or enzymic action or by both, appears probable. 

 That they can enter a flower also through the petals or the style, has 

 been found by the writer. It is believed that under field conditions 

 the number of infections resulting from the entrance of bacteria 

 through these infection courts is small. 



Although some workers report infection through either stomata or 

 liydathodes, the writer was unable to consistently obtain infection 

 through these openings. Artificial inoculation on uninjured apple 

 and pear seedlings, indoors and out, failed to give consistent evidence 

 of such a mode of ingress. Infection of pear and apple leaves can be 

 readily obtained through needle or insect punctures. It has been the 

 w liter's experience that such inoculations rarely produce infection of 

 the twig, as the bacteria usually die before reaching the base of the 

 petiole. 



After the bacteria have been introduced into the interior of young, 

 rapidly growing, apple shoots, there appears to be a delay before 

 much new tissue is invaded. No instances were found in which the 

 bacteria progressed as much as an inch during the first day after 

 inoculation. Beginning twenty-four hours after inoculation, the rate 

 of progress, on an average, was little over 1 inch a day. No cases of 

 8 to 10 inches of migration a day, as reported by some workers, were 

 found, although an attempt was made to maintain optimum conditions 

 for migration. 



For a number of years, insects were considered the chief disseminat- 

 ing agents of fire blight. In 1922, Gossard and Walton again placed 

 this phase of the problem in question. That insects are the principal 

 vectors of the fire-blight germs under certain conditions can hardly 

 be contested, in view of the careful work done by a number of workers. 

 The writer's experiments and field observations bearing on this ques- 

 tion, point strongly to insect transmission from blossom to blossom. 

 But how are the first blossoms inoculated! If oozing cankers occur 

 immediately above open blossoms, there is no apparent reason why 

 meteoric water cannot inoculate them, since blossoms are easily inocu- 

 lated by atomizing. However, the number of blossoms so inoculated 

 would be relatively small when all cankers and dead twigs are carefully 

 excised. 



(Jossard and Walton have held that pollinated blossoms are less 

 subjeel to infection than are unpollinated blossoms. The data given 

 in this paper show that increasing age of blossoms, and not pollination, 



