468 MXGOUS DISEASES OF PLANTS 



largely of trees that are affected by this " punk." The fungus is 

 also common in pine forests of northern Europe, occurring there, 

 as well as in parts of America, on the spruce. According to 

 Hartig, trees are more subject to this fungus in woods exposed to 

 strong winds, since the breaking of limbs of older trees by any 

 cause invites infection. 



The phenomenon of infection and the spread of the fungus 

 within the tree are doubtless accomplished in a manner similar to 

 the cases already described. The wood pervaded by the fungus 

 assumes from the first a deep red-brown color. There is no 

 checking, in the proper sense, although occasionally the annular 

 rings may in one or more regions be readily separable. The chief 

 characteristic, however, so far as the effect upon the wood is con- 

 cerned, is to be found in the development of bleached pits or 

 pockets. The formation of these may be readily understood when 

 it is ascertained that the action of the mycelium is first to delignify 

 the cells, then to dissolve the middle lamellae, so that the cells are 

 set free prior to general dissolution. The wood is therefore in 

 certain areas transformed to more or less pure cellulose and con- 

 sequently bleached in appearance. The pockets appear more or 

 less circular in cross section, and vary in shape from ovoidal to 

 long-cylindrical. The pockets are at first to be found chiefly in the 

 spring wood portion of the annular ring. The mycelium is yel- 

 lowish in color and is not massed in strands in the pockets. 



In the pine the sporophore is almost invariably formed in a 

 wounded area, and the fruit body may be in the form of an in- 

 crusted, brown-black stratum, or as a hoof-shaped bracket. These 

 sporophores are perennial, and for a few years the annular layers 

 which are developed successively upon the fruiting surfaces in- 

 crease the size of the fruit body. Subsequently, however, there 

 may be no increase in size from the deposition of new layers, or 

 the strata may be of smaller extent, in case of the death of a por- 

 tion of the last-formed annular layer. The fruit body may attain 

 a considerable age, and each year or season of growth will be out- 

 lined by a somewhat prominent concentric ring, or surface ridge. 

 The lower or marginal ridge, including the hymenial surface, is of 

 a light brown color, but older ridges become black and very irregular 

 in outline. A section of a sporophore shows a layered structure, 



