SOURCE OF INFECTION. jak 
spore find their way through the skin of the apple. The most common 
belief expressed by writers upon this subject is that the fungus enters 
through insect punctures or some other abrasion of the skin, and it has 
also been suggested that the fungus coudd probably enter through the 
unbroken skin. The writer’s observations would indicate that a wound 
is not at all necessary for successful infection and that the fungus most 
commonly penetrates the skin. Several hundred points of infection 
were examined without finding any indication of a previous puncture. 
_A large percentage of the apples on the untreated trees used as checks 
in the spraying experiment had from one hundred toa thousand points 
of infection, and in many cases the spots were so thick that when only 
one-sixteenth of an inch in diameter they overlapped. In the labora- 
tory, infections were easily made by dropping water containing spores 
on the unbroken skin of an apple in a moist chamber. 
BITTER-ROT CANKERS ON THE BRANCHES. 
In 1902 it was discovered by Mr. R. H. Simpson, of Illinois, that 
limb cankers were associated with outbreaks of bitter-rot. Messrs. 
Burrill and Blair of the Illinois Agricultural Experiment Station, and 
Messrs. von Schrenk and Spaulding’, of the Mississippi Valley Labora- 
tory of the Bureau of Plant Industry, working independently, soon 
established the relationship of these cankers to the disease on the fruit 
and proved by inoculation tests that these cankers were caused by the 
same fungus that attacks the fruit. 
In describing this form, von Schrenk and Spaulding’ state that 
‘*The cankers found on apple trees in [lhnois appear as blackened 
depressions on apple limbs of various sizes, from last year’s fruit 
- spurs to limbs 3 to 4 inches in diameter. Thus far the cankers have 
not been found on the main trunk. On these limbs rounded or oblong 
sooty-black sunken spots occur from one to several inches long, which 
have more or less ragged edges.” Limb cankers occur abundantly in 
the Virginia orchards, but the writer has so far been unable to find 
the bitter-rot fungus associated with any of them. However, limbs 
of young apple trees on the grounds of the United States Department 
of Agriculture inoculated with bitter-rot spores rapidly developed 
these cankers. 
SOURCE OF INFECTION AND SPREAD OF THE DISEASE. 
The question as to the chief source of the first infection each year 
has not been satisfactorily settled, nor is it definitely known how the 
a Cire. 58, Ill. Agr. Exp. Sta., July, 1902, and Bul. 77, Ill. Agr. Exp. Sta., 1902, pp. 
300-397. 
b Bul. 44, Bureau of Plant Industry, U. S. Dept. of Agriculture, 1903, pp. 29-86. 
CLG pyol. 
