13 



sepavrtto, except here and there where small portions of the undis- 

 solved primary lamella still unite them. In the illustrations (PL VII, 

 fig. 3) these parts are black. When they disappear the halves become 

 free— the stage shown in PI. VII, fig. 4. The dotted lines in this figure 

 represent in perspective the margins of the hole, and two large holes 

 in the tangential wall, where some of the hyphte had passed through, 

 are also shown. The holes are exceedingly numerous, puncturing the 

 cell in all directions. 



In the first stages of corrosion of the pits a change in the medullarv 

 rays l)ecomes evident. The walls are very rapidly disintegrated, and 

 even before there is much indication of change in the tracheids the 

 medullary rays have disappeared entirely, leaving long holes, which 

 extend in all directions from the original center of attack (PI. VII, 

 fig. 1). By the time the pits of the tracheids are gone the piece of 

 wood has turned yellowish brown and has become very ])rittle. The 

 numerous holes made by the hyph<\3 and the absence of the medullary 

 rays and the primary lamella readily explain why such wood crumbles 

 into a fine powder at the slightest touch. The parts that exist longest 

 are held together by only the infinite number of fine hyphfe which 

 surround them. In certain portions of the wood there are holes 

 which show no disintegration whatever into cellulose. The small hole 

 shown at the bottom of PI. Ill is one of this kind. 



, THE MYCELUM. 



The mycelium of the fungus is found in the wood between the holes, 

 as well as in the sound ( ?) wood around the cavities. In the newly 

 invaded portions of the trunk it is almost colorless. The hyphtv are 

 of various sizes, and the larger ones extend longitudinally vfithin the 

 tracheids, giving ofi' branches which penetrate the walls in all direc- 

 tions. The hyphse never fill a tracheid completely. Within the holes 

 the mycelium forms large sheets and webs, the latter looking very 

 much like ground spiders' webs. When first found in the holes, the 

 mycelium of the sheets is composed of thick-walled hyphiv of a tawny 

 yellow color. During the later stages of decomposition the tangential 

 plates above referred to are found completely interwoven with the 

 hyphw. These plates hold the ultimate pieces of the wood fibers in 

 position, surrounding them on all sides, and finally absorb them entirely. 



PROGRESS OF THE DISEASE. 



The condition in which the holes are found makes it possible to 

 describe their formation. The fungus apparently enters the trunk 

 through a dead branch, and when the hyphse reach the heartwood 

 they grow both upward and downward. What factors determine the 

 spot where disintegration of the wood begins is as yet unknown. 

 At one point, generally a distance from the place of entrance, some 



