Studies on the Fire-Blight Organism, Bacillus amylovorus 20 



made from six of the twigs measuring *4 inch in diameter, to verify 

 the conclusions reached by the observations. In each case the isolations 

 checked with the observations. 



From the foregoing data it is evident that small twigs may serve as 

 "hold-overs" for fire blight. In Plate II, 3, drops of ooze which are 

 sometimes found on these small twigs are shown. It is at once apparent 

 that even though only a small number of twigs might serve as 

 "hold-overs," this fact would seriously handicap any eradication 

 campaign. 



Except when directly associated with a living part of the host plant, 

 the bacteria in nature are generally believed to die rather quickly. 

 The reports of Arthur, Hotson, and Waters, already noted, do not sub- 

 stantiate this belief. Dr. Thomas obtained virulent organisms twelve 

 months after infected limbs had been brought into his laboratory. Dr. 

 W. H. Burkholder, of the Cornell station, working with Bacterium 

 ftaccumfaciens Hedges, obtained pathogenic bacteria from herbarium 

 specimens (leaves of Phaseolus angularis) five years old. 



A number of yearling Transcendent crab-apple trees which were 

 infected with Bacillus amylovorus and showed large drops of ooze, 

 were brought into the laboratory by the writer in May, 1925. Cultures 

 made from the dried ooze at three-months intervals yielded the organism 

 each time for two years and three months. The last cultures, at two 

 and one-half years, failed to produce the organism, but it is possible 

 that the failure was due to teehnic rather than to loss of viability of 

 the organism. The initial bouillon cultures were allowed to incubate 

 for four days before dilutions were made, and were heavily charged 

 with contaminating organisms. 



Neither B. amylovorus nor any other bacterial plant pathogene is 

 known to form endospores. Yet it seems almost unbelievable that vege- 

 tative forms of bacterial cells will live for five years on dried herbarium 

 specimens or for two years as dried ooze on apple twigs. Of course 

 these conditions do not duplicate those of the field, especially in regard 

 to rapid fluctuations in temperature and humidity, and to sunshine. 



The work of Nixon (1927) suggests that there may be resting forms 

 of these organisms, as cysts or involute forms, which may be more 

 resistent to adverse conditions and may approximate in function and 

 characteristics the endospores formed by such species as Bacillus 

 botulinus. The nature and properties of the matrix in which the bac- 

 terial cells are embedded in the ooze deserve further study in this 

 connection. 



MODE OF ENTRANCE INTO BLOSSOMS 



Arthur (1886:272), whose three years of work on fire blight (1884 

 to 1886) were begun shortly after Burrill discovered the causal organ- 



