Studies on the Fire-Blight Organism, Bacillus amylovorus 13 



ferent cultures were inoculated into the terminals of each tree, one 

 culture to a terminal. If differences in virulence or adaptation to dif- 

 ferent climatic conditions were inherent in any culture, by inoculating 

 the cultures on the same trees it was thought such differences would 

 become apparent. At the time of checking the results, the terminal 

 growth killed by blighting was measured. Natural inoculations were 

 few in number during the progress of the tests. It is therefore 

 assumed that when a terminal blighted, the culture inoculated into it 

 was the causal factor. The error resulting from this assumption is 

 thought to be negligible. Before each series of inoculations, all strains 

 used were transferred to bouillon tubes three times, at intervals of 

 forty-eight hours, to insure that actively growing bacteria were present 

 in all cultures. Results of these tests are summarized in table 3. A 

 dasli and number — for example, A-1 — indicates that the original cul- 

 ture was inoculated into apple and reisolated. 



TABLE 3. 



Summary of Results of Inoculations on Pear Seedlings with Different 

 Cultures 



It is evident that there is a marked variation in the ability of dif- 

 ferent cultures to infect seedling pear trees. Culture C should be omitted 

 in any comparisons, as the odds are heavily in favor of the one infec- 

 tion with this culture being accidental. Culture C was indistinguishable 

 from other cultures on artificial media. Cultures T and S infected about 

 six times as many trees as did culture D, although after infection 

 occurred there was not much difference in the length of the twig killed. 

 Culture E was able to infect but half as many trees as did culture T, 

 and when infection occurred it was able to kid but half as much twig 

 growth. It should be noted that cultures D and E were isolated at least 

 twelve months earlier than were any other of the cultures used in these 

 experiments. Culture Cal grew more rapidly and luxuriantly than did 



