28 



A. L. PlERSTORFF 



be hosts for the organism. All attempts to isolate B. amylovorus from 

 the soil have met with disappointment. 



It was early recognized that after twigs or branches were cut from 

 a tree, the bacteria died, in a majority of the branches, in a few days. 

 Arthur (1887 b) was one of the first to make tests on the longevity of 

 the fire-blight organism. He found viable bacteria in some infected 

 branches nine months after they had been removed from the tree and 

 thrown into an open cistern. No inoculations are recorded in which 

 the bacteria isolated from the inner bark of these branches were used. 

 Fulton (1911), in Pennsylvania, reported that of thirty-five pruned 

 twigs which were left lying on the ground, thirty-one contained no living 

 bacteria after seven days. Hotson (1916), in Washington, extended 

 the time that fire-blight bacteria may live in pruned branches to a 

 month. A limb placed in the sun in his laboratory, where the tempera- 

 ture during the day was usually from 40° to 50° C, contained viable 

 fire-blight organisms for twenty-eight days. Waters (1922) has shown 

 that living bacteria were recovered from dried exudate after a period 

 of nine months. In Colorado, Sackett (1911) found approximately 25 

 per cent of the eighty-three cankers which he examined to be ''hold- 

 over" cankers. Stewart (1913:346) reports isolating the organism 

 from pear twigs less than 1 centimeter in diameter, and from pear- 

 seedling trunks about y 2 inch in diameter, during the dormant season. 

 Dr. H. E. Thomas examined more than one hundred small twig cankers 

 of apple in 1923 about blossoming time, and found no living fire-blight 

 bacteria. 



Observations on "hold-over" blight were made by the writer in 1925 

 and 1926 at blossoming time in an apple orchard near Ithaca. The 

 results of these observations are presented in table 4. Cultures were 



TABLE 4. 



" hold-ovek " can'kers of bacillus amylovorus on apple at blossoming 

 Time 



