100 MANUAL OF FRUIT DISEASES 
probably never proceeds more than four inches above the ground 
on account of a lack of moisture. In living or dead roots and 
root-stocks the pathogene may live for several years. As al- 
ready mentioned under Symptoms, the mushroom itself develops 
from the rhizomorphs in the months of September, October and 
early November, and rarely in the spring. The mushroom 
obtains food from the rhizomorphs, and maturity is thus reached 
in a very short time. At full growth the mushroom varies 
from three to seven inches in height; the cap measures from 
two to six inches across; the cap is conical, yellowish at first 
but becoming dark with age; the gills are white, with reddish 
brown spots; the stem is swollen near the base, and possesses 
an annulus which is conspicuous in early stages of development 
but sometimes only slightly developed or even wanting. . The 
mushrooms often grow in clusters, and, while edible, are not 
choice. 
The system of rhizomorphs which attacks the roots actually 
travels through the soil from tree to tree. Thus infection occurs 
underground. From the gills of the mature fruiting bodies, or 
mushrooms, spores are liberated in great numbers. These 
spores are carried through the air for long distances and doubt- 
less account for isolated cases of Armillaria root-rot. The 
spores germinate in the soil, feeding on humus, and produce 
mycelial threads which unite to form the cord-like strands, or 
rhizomorphs. 
Control. 
If trees are once affected, there is little hope of saving or curing 
them. Nursery inspection is not reliable. The rhizomorphs 
may be broken off accidentally or intentionally, and thus there 
would be no certain evidence of the disease. In sucha case, too, 
the tree concerned may have just been infected. In this way a 
diseased tree does not appear to be infected, and therefore it is 
certified. Thus the fungus is carried in nursery-stock. 
As with a great many plant diseases, the elimination of the - 
