12 BULLETIN 684, U. S. DEPARTMENT OF AGEICULTURE. 



slits on the Missouri branches the dark sunken band was 3 to 4 mm. 

 in width. There was no development whatsoever in the case of the 

 Jonathan, either at this time or subsequently. On August 30 the 

 black sunken bands about the slits on the Ben Davis branches were 

 from 2 to 6 mm. in width, while those on the Missouri branches were 

 slightly larger. The inoculated branches were not examined again 

 until June 18, 1916. The cankers had not changed perceptibly. 

 The chief thing to be noted was that there was no isolation of the 

 blackened bark on three of the Ben Davis branches and on three of 

 the Missouri branches. These branches, though of equal age, were 

 not nearly so large as the others, which were rapidly growing water 

 sprouts. The cankered areas on the water sprouts were being rapidly 

 healed over by the formation of callus, and the blackened bark had 

 been partly shed. The cankered branches were removed, brought to 

 the laboratory, and placed in moist chamber for 24 hours. Acervuli 

 of the fungus were produced in great abundance, and when reiso- 

 lated in pure culture the organism was reidentifiecl as Glomerella 

 oingviata. 



The question arises as to why quickly developing young cankers 

 on vigorous young branches and water sprouts should not live and 

 develop through the following season. Apparently this is what hap- 

 pens : The host has its period of most rapid growth in the spring. In 

 the case of young branches and water sprouts, growth is particu- 

 larly rapid at this time. The fungus, on the other hand, does not 

 begin active growth until hot weather begins. Vigorously growing 

 branches, such as water sprouts and young twigs, are able, therefore, 

 through the growth of surrounding tissues to utterly isolate the 

 young cankers and begin the formation of callus at their margins 

 while the fungus is still dormant. 



To test the effect of cool weather and to see if late infections would 

 develop, Ben Davis and York Imperial branches were inoculated at 

 Arlington Farm, Va., on October 5, 1915. The weather, though 

 cool, was moist, but no perceptible growth was made about any of 

 the 12 inoculated slits, nor was any growth made during 1916. 

 On the contrary, the slits had entirely healed over by July 1, 1916. 



Employing the same methods as in 1914 and 1915, the writer made 

 several series of inoculations at Arlington Farm, Va., in 1906, using 

 cultures of the fungus from a canker collected in Arkansas during 

 the preceding autumn. In Table I the terms " margin intact " and 

 " margin cracked " mean in the former case that the blackened bark 

 of the canker is continuous with that of the uninfected portion of 

 the branch and in the latter that it has been broken away from the 

 bark of the uninfected portion. No separate notes were made con- 

 cerning individual inoculations on the same limb, for the reason 



