40 A. L. PlERSTORFF 



in 1927. In 1928 his Jonathan and Grimes trees were free from blos- 

 som blight, but his Rome Beauty trees showed from 60 to 80 per cent 

 of blossom infection. No blighted twigs could be found by the writer 

 on the Rome Beauty trees. The Jonathan trees contained many dead 

 twigs from the previous season, and several "hold-over" cankers were 

 found. The explanation appears to be that the two earlier varieties 

 shed their petals before the insects became contaminated, while the 

 Rome Beauty, blossoming later, became inoculated. 



Again, in 1930, observations were made bearing on the dissemination 

 of the fire-blight organism in apple orchards of southern Ohio. On 

 April 14, the early varieties had opened about one-fourth of their 

 blossoms and Rome Beauty was in an early pink stage. A week later 

 the petals were falling from the early varieties, and Rome Beauty was 

 in full bloom two days later. Petal fall on Rome Beauty occurred 

 about April 28. 



During the period from April 7 to April 28 there was never more 

 than 0.04 inch of precipitation in one day in Lawrence County, Ohio. 

 B}' May 5, a severe epiphytotic of blossom blight was apparent in 

 Lawrence, Gallia, Meigs, and Athens Counties. In most orchards no 

 active "hold-over" cankers could be found, and yet up to approxi- 

 mately 90 per cent of the blossoms were blighted in extreme cases. 

 No orchard was found entirely free from blossom blight. Comparable 

 conditions were found on twenty-one farms in Brown and Adams Coun- 

 ties on May 19 and 20. The scarcity of sources of inoculum and the 

 virtual absence of rain during the blossoming period, together with 

 the observed incidence of blossom blight, compel the conclusion that in 

 this epiphytotic rain was of no consequence as an agency for the dis- 

 semination of the organism. The observed phenomena may be 

 explained, on the other hand, on the assumption that pollinating insects 

 served as the agency for transporting the organism from blossom to 

 blossom and from orchard to orchard. 



RELATION OF POLLINATION AND AGE OF BLOSSOMS, TO INFECTION 



"While some of the earliest workers on dissemination of the fire- 

 blight organism (Arthur in 1885, 1886, and 1887, Waite in 1896, 1898, 

 and 1902, and D. H. Jones in 1909) recognized that open blossoms offer 

 an avenue of entrance for the bacteria, they apparently did not study 

 the susceptibility of blossoms in relation to age or pollination. Gos- 

 sard and Walton (1922) brought this phase of the problem to our 

 attention. They concluded "that blossoms which have been pollinated 

 for 72 hours are not likely to be inoculated with fire blight and that 

 susceptibility to inoculation does not exist in blossoms that have been 

 pollinated for 144 hours." 



