22 DISEASES OF DECIDUOUS FOREST TREES. 



good examples of this type of fungus. Their black fruiting bodies 

 are usually found on the dead or dying wood of the branches or 

 trunks of trees, particularly of the oaks and beeches. 



CHESTNUT BARK DISEASE. 



The chestnut (Castanea dentata (Marsh.) Borkh.) has been almost 

 completely exterminated over extensive areas adjacent to the city 

 of New York by a fungus known as Valsonectria parasitica (Murrill) 

 Rehm. (54, 55, 56, 60, 61, 62, 70). It causes patches of the bark to 

 die by attacking the cambium and other soft tissues of the bark, and 

 extends in all directions until the branch or trunk is girdled. This 

 leads to the death of those parts above the girdling, and in this way 

 if the main trunk is attacked the entire tree may be killed. The 

 disease attacks the bark on the twigs, branches, and trunk without 

 respect to its thickness. How the fungus gains entrance is uncertain, 

 but inoculation experiments (60, 61) seem to show that it is able to 

 enter only through injuries to the bark. The affected bark has a 

 blackened appearance, is somewhat shrunken, and after a time is apt 

 to be thickly covered with projecting brown or orange or greenish 

 yellow colored bodies, which are about one-sixteenth inch in diameter 

 at the base, often long and twisted or curled, and taper to a slender 

 tip. These are the fruiting bodies of the fungus and are very char- 

 acteristic of this disease when the weather is moist enough for their 

 formation. 



The disease has already spread south to Bedford County, Va., west 

 to Lancaster County and Northumberland County, Pa., and north 

 to Massachusetts. The Japanese chestnut (Castanea crenata Sieb. & 

 Zucc.) is in general resistant, although single trees of this species have 

 taken the disease. Immunity tests of all known varieties of chest- 

 nuts are now in progress by this Department (55, 56) No adequate 

 preventive measures seem to be known at present, so that this disease 

 is an especially threatening one in the Eastern States. 



A similar disease has been noted by the writers upon the Spanish 

 oak (Quercus digitata (Marsh.) Sudworth) in the Appalachians, 

 especially in Virginia and western North Carolina. This disease is 

 manifested in the drooping of the leaves and their ultimate drying 

 up, caused by a stoppage of the water supply in the branches by an 

 apparently undescribed species of Cenangium. 



ROOT-ROTS. 



Of the fungi which attack the living roots, two deserve particular 

 notice. Diseases of the root system of broadleaf trees are usually 

 classed together under the term "root-rots." By this is meant a 

 disease which shows in the tree tops by a gradual dying of the branches 



149 



