Studies on the Fire-Blight Organism, Bacillus amylovorus 33 



mode of functioning of the bacteria in most instances under natural 

 conditions. That occasionally the bacteria may gain entrance through 

 the stigmas is indicated. Killing of the style by the bacteria while 

 the remainder of the flower is healthy is shown in Plate III, 5. No 

 infection is apparent in the nectariferous region. In approximately 

 forty-eight hours more, the bacteria would have reached the base of 

 the style, judging from previous invasion. This substantiates some 

 of the results obtained by stigma inoculations, given in table 5. In 

 none of the sections made by the writer did infection and invasion occur 

 through the epidermis of the receptacle below the sepals (Plate III, 6, 

 region D). This, however, does not preclude such a possibility, espe- 

 cially when the opening flowers are infested with aphids. Needle 

 punctures with bouillon produce disease readily in this region of the 

 flower. Miller (1929) records infection through the sepals of unopened 

 apple flowers. 



LEAF INVASION 



In 1915 Heald reported that fire-blight bacteria had been found 

 invading apple leaves. He expressed the opinion "that the bacteria 

 enter the intercellular spaces through the water-pores and also by the 

 stomata to some extent ..." Later (1927) he presented additional 

 notes on natural leaf infection, and reported experiments in which 

 inoculations on pear and apple caused both marginal and central leaf 

 lesions similar to those observed in nature. Hotson (1916) found many 

 pear leaves infected on the Pacific coast, but observed few twig infec- 

 tions resulting from leaf infection. Stewart (1913:339) figures two 

 pear shoots on which some of the leaves have blighted, owing, he 

 says, to infection at the base of the petiole. Possibly the bacteria 

 gained entrance through the leaves instead of in the manner described 

 by Stewart. 



Brooks (1926:694), working in Wisconsin, reached the following 

 conclusion: "The nectaries of blossoms, and possibly the hydathodes 

 of very young leaves, seem to be the only natural openings through 

 which blight infection of apple takes place. All attempts to secure 

 stomatal infection failed." He found that infection would take place 

 through wounds in leaves up to thirty-six hours after injury. Miller 

 (1928), working in the same laboratory, states that he "has induced 

 at will abundant infection of young shoots and unopened blossom buds 

 of apple and pear by spraying them with a suspension of the fire- 

 blight bacteria . . ." He finds that the organism will also enter 

 the stomata of young leaves and cause infection. Tullis (1929) reports 

 successful twig inoculation on apple and pear by first sprinkling the 

 seedlings for five hours, then placing a drop of inoculum on the leaves 

 and sprinkling overnight. 



