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 such a 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 



