DISEASES CAUSED BY WOUND FUNGI. 43 



The fruiting bodies of Fomes nigricans appear on diseased trees as 

 single, largo, more or less hoof shaped bodies; there may be but one 

 of these on a tree, or up to six or eight, but in no case is more than 

 one fruiting body found at one point. The sporophores are large, 

 woody structures, resembling those of Fomes igniarius. It has been 

 held by Murrill (58) that Fomes nigricans is but a form of Fomes 

 igniarius. 



The top of the sporophore shows a number of concentric ridges in 

 which large numbers of sharply defined shallow fissures appear as the 

 sporophore grows older. These fissures extend radially and trans- 

 versely across the top and give the appearance of numerous black 

 lines. The top as a whole is smooth, differing in this respect from 

 many types of Fomes igniarius, in the older forms of which the top is 

 very rough; the older portions of the surface are jet black. This is 

 likewise usually true of the younger layers, although we have noted 

 instances where the most recently formed outer edge is dark brown 

 in color. One of the most characteristic properties of the top of the 

 sporophore is its intense hardness. When cut into, this hard layer, 

 which is usually about one-sixteenth of an inch in thickness, has a very 

 characteristic horny texture. The lower surface of the sporophore is 

 rounded, and usually dark brown in color; the pores are very minute 

 and regular. The substance of the sporophore is tough and almost 

 woody. The sporophores are of all sizes, varying from an inch to 10 

 or 12 inches in width. As a rule, when perfect they are characterized 

 by great regularity in their proportions, and when once recognized, 

 one can hardly fail to distinguish this species. 



Fomes nigricans sometimes forms very curious fruiting bodies on 

 birches, the cause for which has not yet been definitely determined. 

 For many years observers and collectors in the Northern States have 

 reported finding irregular, black, jagged masses, having the appear- 

 ance of dried, hard pitch, growing out from wounds on birch trees 

 (PI. VI, fig. 2). These masses look like large warts. They are jet 

 black in color, very deeply fissured and broken, and of all conceivable 

 shapes. They increase in size from year to year in a very irregular 

 way without any signs of pore formation. The mass of these bodies 

 is very hard and when examined closely shows that it is composed of 

 masses of dark brown hyphae the walls of which have become exces- 

 sively thickened, giving the whole a woody texture*. The writers 

 have observed these black structures for a number of years without 

 being able to identify them; the senior writer suggested tentatively, 

 some years ago, that they might be undeveloped sporophores of 

 Fojnes igniarius, 



In his recent paper Lindroth (48) describes similar bodies growing 

 on birches in Europe, and definitely calls them abortive bodies of 



149 



