48 A. L. PlERSTORFF 



reduces the susceptibility to fire-blight infection. It is a well-established 

 fact that the blight pathogene thrives best in rapidly growing tissue. 

 On this basis one might expect pollinated blossoms which are actively 

 growing to be more subject to attack than unpollinated ones. There 

 is some evidence in this paper in support of this hypothesis. 



SUMMARY 



Additional information is presented in this paper on the suscepti- 

 bility of rose, strawberry, and Crataegus oxyacantha. Japanese quince 

 (Chaenomeles lagenaria) and Photonia villosa are added to the list 

 of suscepts. 



It is held that Bacillus amylovorus can live in an acid medium of 

 pll 4.60, that it can withstand a temperature of -183° C. for ten 

 minutes, and that heating to 48° C. for ten minutes does not always 

 inhibit growth. 



Positive evidence is given for the formation of the enzymes sucrase 

 (or invertase), maltase, inulase, and arbutase by B. amylovorus; nega- 

 tive results are reported for amylase, pectosinase, pectase, pectinase, 

 cellulase, amygdalase, and trypsin. 



A toxic substance was found in green pear fruits which were rotted 

 by the fire-blight organism. 



Viable bacteria were isolated from "hold-over" cankers on twigs as 

 small as one-fourth inch in diameter. 



Pathogenic bacteria were obtained from infected limbs after these 

 had been kept in the laboratory for two years. 



The commonest mode of entrance into blossoms was found to be 

 through the nectariferous surfaces ; occasional entrance from natural 

 and artificial inoculation was found to occur through the petals and 

 the styles. 



Naturally inoculated pear leaves were found on trees infested with 

 leaf hoppers. Artificial inoculation by atomizing young, rapidly grow- 

 ing, pear and apple trees failed to produce infection if the trees were 

 free from insects. 



B. amylovorus was found to progress slowly for the first twenty-four 

 hours after inoculation into young apple shoots; thereafter, for a 

 period of eight days, migration was found to proceed at the rate of 

 about 1 inch a day. 



Meteoric water did not appear to spread the blight bacteria from 

 blossom to blossom. 



Increasing age of blossoms was shown to decrease susceptibility to 

 fire blight. Pollination of blossoms was found to have little, if any, 

 influence on susceptibility. 



