April, '12] METCALF: CHESTNUT BARK DISEASE 223 



northern border of Massachusetts and from Saratoga Countj^, X. Y., 

 to the western border of Pennsylvania and the southern border of 

 Virginia, scattering areas of infection are knowTi to occur and may be 

 expected at any point. There is not yet the slightest indication of any 

 cessation of spread or virulence of the disease, unless possibly locally 

 in Virginia. The actual loss of property to date resulting from this 

 disease cannot be estimated as less than twenty-five millions of dollars. 



So far as is now kno^Mi, the bark disease is limited to the members 

 of the genus Castanea. The American chestnut, the chinquapin, 

 and the cultivated varieties of the European chestnut are all readily 

 subject to the disease. Only the Japanese and some other east Asian 

 varieties appear to have any resistance. 



The disease is caused by a fungus, Diaporthe parasitica. When 

 any of the spores of this fungus gain entrance into any part of the 

 trunk or limbs of a chestnut tree they give rise to a spreading canker, 

 which soon girdles the tree. If the part attacked happens to be the 

 trunk, the whole tree in consequence is killed, perhaps in a single 

 season. If the smaller branches are attacked, only those branches 

 are killed, or only those portions of branches beyond the point of 

 attack, and the remainder of the tree may survive for several 3'ears. 



Limbs with smooth bark attacked by the fungus soon show dead, 

 somewhat discolored, sunken areas, which continue to enlarge and 

 soon become covered more or less thickly with yellow, orange, or 

 reddish-brown spots about the size of a pinhead. These spots are 

 the pustules of the fruiting fungus. In damp weather or in damp 

 situations, masses of summer spores are extruded in the form of long, 

 irregularly twisted strings or "horns," which are at first bright 3'ellow 

 to greenish yellow or even buff, becoming darker with age (Fig. 2). 

 If the canker is on the trunk or a large limb with very thick bark 

 there is no obvious change in the appearance of the bark itself, but 

 the pustules show in the cracks and the bark often sounds hollow 

 when tapped. After smooth-barked limbs or trunks are girdled the 

 fungus continues to grow extensively through the bark, sometimes 

 covering the entire surface with reddish-brown pustules (Fig. 3). 



After a branch or trunk is girdled, the leaves change color and sooner 

 or later ^\ither. Such branches have a very characteristic appearance 

 and can hardly be mistaken for anything else, except in certain local- 

 ities where the work of t\ng-girdling insects may produce a similar 

 appearance in the spring. In case the girdling by the fungus is com- 

 pleted late in the season, the leaves of the following spring assume a 

 yelloAAish or pale appearance and do not develop to their full size. 

 If the girdling is completed between spring and midsummer the leaves 

 may attain their full size and then turn a somewhat characteristic 



