

DISEASES CAUSED BY WOUND FUNGI. 45 



times that the writers have found it, particularly in the centra] United 



States, it is fairly common on both the while 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 hum rarely, and 

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

 attacked by insects. Even where the insects do nol destroy them, 

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

 into insignificant black masses, which can be recognize! I with difficulty. 



BLACK LOCUST DISEASE CAUSED BY FOMES BIMOSUS. 



The black locust (Robinia pseudacacia) is universally attacked by 

 yellow-rot, which completely destroys the heartwood of living i 

 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 locusl trees are 

 destroyed. 



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

 locust borer (Cyllene robiniae) . Wounds are frequent in older trees, caused by the brit- 

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

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

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

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

 are very striking. The hard, resistant wood is transformed into a eofl yellow or 

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

 of the wood is wholly gone in completely decayed wood, which can In- 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 thread- 

 growing outward through some of the large medullary r.-i \ s. 



The sporophores of Fomes 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 of from 30 to 35 degn 

 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 Fomes f omental 

 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 \cr\ distinct in the 

 younger part of the sporophore, but become almost obliterated a 

 sporophore grows older. The youngest part of the sporophoi 



149 



