76 MANUAL OF FRUIT DISEASES 
mental trees are often filled with cement or asphaltum blocks. 
Whether or not this practice is to be followed in the apple or- 
chard depends upon the extent of the injury and the exposure 
of the orchard to wind. As a general rule the filling of cavities 
with any substance is not within the province of the practical 
orchardist; the operation does not pay. But in any case the 
interior surface of the cavity should be coated with a wound- 
dressing. 
REFERENCES 
Schrenk, H. von, and Spaulding, P. Diseases of deciduous forest trees. 
White heart-rot caused by Fomes igniarius. U. S. Agr. Dept. 
Pl. Ind. Bur. Bul. 149: 25-37. 1909. 
Atkinson, G. F. Studies of some shade tree and timber destroying 
fungi. Polyporus igniarius. Cornell Univ. Agr. Exp. Sta. Bul. 
193 : 239-247. 1901. 
Hartig, R. Die Zersetsungserscheinungen des Holzes. Polyporus 
igniarius Fr., pp. 114-123. 1878. 
BuisTER-CANKER 
Caused by Nummularia discreta Tul. 
This disease, which is known as blister-canker, and Illinois 
canker, was first given attention in Illinois in 1902. Since 
that time it has been reported from the following states: 
Arkansas, Indiana, Iowa, Kansas, Missouri, Ohio, Oklahoma, 
Nebraska, New Hampshire, New York, Virginia and West 
Virginia. Besides its occurrence in the United States, the blister- 
canker is found in Germany, Italy and Cuba, although it does not 
appear to have assumed great importance in these countries. 
In certain states, as, for example, Missouri, and the southern 
portions of Illinois, Indiana and Ohio, this is the most injurious 
canker disease of the apple. It is said that within the last few 
years orchardists in Kansas, Missouri, Oklahoma and Nebraska 
have lost more than a million trees from it. The injury con- 
