CAUSE OF THE DISEASE. 9 
crack and break off. The fungus had nearly girdled the specimen 
shown in the center of this figure. The control slits had healed over 
nicely and showed no roughening or adjoining dead areas. 
The trees selected for these inoculations were healthy specimens 
near the center of a 4-year-old orchard that was in fairly good growing 
condition and which was some distance away from the nearest 
orchard in which the disease was prevalent. 
Branches thus diseased through inoculation with spores of the 
fungus were brought into the laboratory, and from the margins of the 
spots or cankers the fungus was reisolated, usually in pure culture. 
In lhke manner the trunks and branches of young trees growing in 
the greenhouse were inoculated. In two months well-developed 
sunken spots possessing all the characteristics of the disease appeared. 
The fungus was reisolated both by plating the spores from the few 
pyenidia which had formed and through cultures from the diseased 
tissues. 
Attempts were made to bring about infection by simply spraying 
spores on branches and on green twigs and water sprouts of the 
current year’s growth, but in no case did the fungus gain an entrance. 
An abrasion or wound seems necessary before infection can take 
place. 
Numerous inoculations made in orchards during the fall of the 
year have been uniformly unsuccessful. It would seem, therefore, 
from these experiments and from the observations as to the size of 
spots due to natural infection that the earlier part of the season is 
the time during which the fungus gains entrance and begins its 
development. 
Since this same species of Phomopsis had also been isolated from 
leaf spots along with Sphaeropsis malorum even as early in the season 
as April, it was thought desirable to test its parasitism on leaves. 
When spores were sprayed on healthy leaves, either in the orchard 
or in the greenhouse, no spotting resulted under ordinary condi- 
tions; but when a seedling apple tree growing in the greenhouse was 
thus sprayed and covered with a bell jar within which the air was 
kept saturated with moisture, an occasional leaf showed a few 
minute spots, from which the fungus was reisolated. However, the 
conditions and not the fungus may easily have initiated the spots, 
after which the fungus might readily have entered. Apple leaves, 
when moistened and covered with a bell jar, are likely to be spotted, 
especially if exposed to strong sunlight. That the fungus will grow 
on such dead spots is shown by the fact that when, in either orchard 
or greenhouse, spores were sprayed on leaves which had previously 
been burned slightly with a hot needle, the fungus infested the dead 
areas and developed pycnidia on them within a week. The leaves 
280 
