4 
SOURCES OF APPLE BITTER-ROT INFECTIONS. Ly 
Since bitter-rot mummies and bitter-rot cankers are the chief 
starting points of the disease for the current season, a comparison 
between them as sources of infection is of interest. (Table III.) 
TABLE III.—Comparison of cankers and mummies as sources of infection. 
Cankers. Mummies. 
Relatively few except on very susceptible varieties. .| May be few or many. 
Spores produced in great quantity............---..-- Spores relatively few, owing to mummies being a 
poor culture medium. 
A more or less perennial source.....-......-.-------- An annual source. 
Directlyinjurious to theitrees.2- 2-22-22. 22+ 22-4 Not injurious to the tree directly. : 
Fungus comparatively well protected from compe- | Fungus not well protected. 
tition with other organisms. 
Relatively hard to find and remove..........-.....-- Rather easily found and removed. 
Located on older twigs or branches (not so advan- | Located among next year’s fruits (advantageous). 
tageous). 
CANKERS OTHER THAN THOSE OF BITTER-ROT. 
In 1915 the writer (10) as the result of some work carried on in 
Arkansas in 1914, showed that the bitter-rot fungus may survive the 
winter in almost any cankered or dead part of an apple tree, includ- 
ing Illinois apple-tree cankers due to Vummularia discreta, dead tips 
of fruit spurs, dead parts of limbs injured by freezing or death of 
roots, branches injured by mechanical means, cankers caused by the 
pear-blight organism (Bacillus amylovorus), and twig cankers 
caused by the apple-blotch fungus (PAyllosticta solitaria). 
In the case of those Arkansas and southern Missouri orchards in 
which the disease has been especially destructive over a period of 
years, it is comparatively easy to isolate the fungus from almost any 
dead portion of the trees. Such orchards which may have in addi- 
tion bitter-rot cankers and bitter-rot mummies show how extremely 
destructive the disease can be and how very important are the agen- 
cies which carry it over from season to season. The fruit of orchards 
in which so many sources of infection survive the winter may be 
utterly ruined at the very first outbreak of the disease. These cases 
are, of course, exceptional ones; yet the writer has seen orchards 
the crops of which were totally ruined within a week, each apple 
averaging approximately 500 infections. In such cases, in which 
infection from wintering-over sources is so heavy, control by spray- 
ing alone is impossible. 
Cankers due to various causes are important sources of infection 
in the Middle West, but they appear to play very little part in the 
infection of fruit in eastern orchards. The writer has found com- 
