130 MANUAL OF FRUIT DISEASES 
Morse, W. J. Spraying experiments and apple diseases in 1913. 
The European apple canker in Maine. Maine Agr. Exp. Sta. Bul. 
223 : 23-24. 1914. 
SUPERFICIAL BARK-CANKER 
Caused by Myzosporium corticolum Edgerton 
In certain of the northeastern states apples and pears are 
affected with a superficial bark-canker. In practically every 
apple or pear orchard of New York and neighboring states there 
is more or less of this disease. But even in those orchards where 
every tree is affected there is no evidence that serious damage is 
being done. Every branch of a tree may be extensively affected, 
while large, bearing limbs commonly exhibit cankers of consid- 
erable extent, but in spite of these facts the disease is probably 
never injurious. Its superficial nature accounts for this in a 
satisfactory manner. 
Symptoms. 
The common occurrence of this disease is sufficient in itself to 
warrant a description. Many growers and even scientists have 
confused the superficial bark-canker with the black-rot canker. 
The former disease, like the latter, is found chiefly on the older 
and larger limbs. But there is no striking depression developed 
in the case of the superficial canker as with the black-rot canker. 
At most there is but a slight sinking of the affected bark. The 
outer bark is killed, and a sharp crevice marks the extent of the 
lesion (Fig. 34). This line of demarcation is prominent and 
takes an irregular course on the affected limb. The originally 
infected areas are small and more or less circular, but large 
cankers of various shapes finally appear as a result of the coales- 
cence of two or more cankers. Accompanying the pathological 
changes in the normal bark minute pustules develop in the 
affected area; these dot the surface and resemble very much 
those on the black-rot canker. (Compare Figs. 13 and 34.) If 
