DISEASES CAUSED BY WOUND FUNGI. 45 



times that the writers have found it, particularly in the central United 

 States, it is fairly common on both the white oak and the red oak. 



Trees 50 to 60 years old frequently show the soft heart-rot without 

 any signs of the sporophores. The latter appear to form rarely, and 

 after their formation are very short lived, because they are readily 

 attacked by insects. Even where the insects do not destroy them, 

 they dry up very soon after they have reached maturity, and shrivel 

 into insignificant black masses, which can be recognized with difficulty. 



BLACK LOCUST DISEASE CAUSED BY FOMES RIMOST S. 



The black locust (Robinia pseudacada) is universally attacked by 

 ydlow-rot, which completely destroys the heartwood of living trees. 

 A detailed description of the changes which are caused by this fungus 

 in the wood of locust trees was published by von Schrenk (80). The 

 disease has been found in practically the entire area where the black 

 locust grows, from Massachusetts to New Mexico. It is especially 

 prevalent in the southern Appalachian forests and in some portions 

 of New Mexico, where a very large percentage of the locust trees are 

 destroyed. 



Infection takes place through older branches and through the tunnels made by the 

 lonisl borer (Cyllene robinicu I. \\0undsarefrequentiiioldertrees, caused by the brit- 

 tle nature of the branches of the locust. The fresh wounds are favorable points for 

 the germination of the spores, and it is an easy matter to find all stages, from trees 

 recently infected to trees where the whole side of a trunk has evidently been infected 

 from one branch. The changes which the fungus brings about in the locust wood 

 arc very striking. The hard, resistant wood is transformed into a soft yellow or 

 brown mass, which, when wet, is more or less spongy. The almost flint-like character 

 of the wood is wholly gone in completely decayed wood, which can be cut almost like 

 cheese. (80.) 



One of the most characteristic features of the decayed wood is that 

 the decay extends out from the center of the heartwood in a series of 

 radial lines. These radial lines are produced by the fungous threads 

 growing outward through some of the large medullary rays. 



The sporophores of Fames rimosus Berk, are large and conspicu- 

 ous. The mature form consists of one or more broad shelves, the top 

 of which meets the lower side at an angle o.f from 30 to 35 degrees. 

 They are usually almost twice as wide laterally as from front to 

 back. In the Southern States, and particularly in the Appalachian 

 Mountain forests, the sporophores have a decidedly hoof-shaped 

 character, almost as much so as those of Fames fomentarius (PI. 

 VIII, fig. 1). Similar hoof-shaped forms have been found by Hedg- 

 cock in New Mexico. In either form the upper surface in older 

 specimens shows a number of ridges which are very distinct in the 

 younger part of the sporophore, but become almost obliterated as the 

 sporophore grows older. The youngest part of the sporophore shows 



149 



