72 MANUAL OF FRUIT DISEASES 
Wuitre Heart-Rot 
Caused by Fomes igniarius (Fries) Gillet 
This disease is far more important in the forest than in the 
orchard. Among some of the trees attacked, besides the 
apple, are beech, aspen, balm-of-Gilead, willow, sugar maple, 
red maple, striped maple, silver maple, yellow birch, butter- 
nut, black walnut, 
oak and_ hickory. 
Most destruction 
is wrought in the 
beech and aspen. 
But as an apple- 
tree heart disease, 
white heart-rot is 
perhaps the most 
prevalent and the 
most destructive 
trouble of this type. 
Although this 
Fic. 20.— Fruiting body of the white heart-rot disease has : been 
pathogene. | known for about 
two hundred years, 
it was not thoroughly studied until 1878. Little has been 
learned since that time, in spite of the fact that the disease is 
world wide in its range. It has been found in practically every 
country of the globe as well as in all the more important islands. 
The causal pathogene does not appear to be limited in its geo- 
graphical range by climatic conditions, being found not only in 
temperate zones, but in the frigid and tropical regions as well. 
Symptoms. 
The characters by which white heart-rot may be recognized 
are of two general types, external and internal. The first 
