A DISEASE OF THE BLACK LOCUST. 27 
in the brown mycelium for some time after all semblance 
to wood structure has been lost. The smallest pieces were 
shown to be wood, which indicates that the destruction is 
one which does not pass through the cellulose stage. 
The mycelium in the newly invaded parts of the wood 
consists of thinwalled, almost colorless hyphae, which 
branch frequently, and penetrate the walls of the wood- 
cells in all directions. The older hyphae are thickwalled, 
and dark brown. They fill the large vessels and the spaces 
formerly occupied by the medullary rays, making a dense 
network. As the hyphae grow outward through the older 
wood, they form the peculiar sheets already described. 
Now and then the hyphae forming the core of a sheet, 
reach the cambium layer and spread from this point in all 
directions, killing the living bark and wood, as has been 
pointed out. A thick felt of hyphae forms in the space 
under the bark, and at times breaks or grows through the 
bark, appearing as a small knob on the outside of the 
trunk. These knobs are light red-brown, and are very 
hard and smooth. They gradually increase in size, and 
when about aninch in thickness, pores form on the lower 
side. 
The young sporophore increases in size, and continues 
to do so for many years. The largest seen was about 
16 inches in diameter laterally, and 8 inches from front 
to back. The mature’ form consists of one or more 
broad shelves, the top of which meets the lower side at 
an angle of about 30°-35° (Plate 2). The shelves are 
usually almost twice as wide laterally as from front to 
back. The upper surface in older specimens is composed 
of a number of ridges which are very distinct in the 
younger part, but become almost obliterated as the spo- 
rophore grows older. The most recent layer forms the 
front rounded edge of the sporophore, and is character- 
ized by the very smooth surface, which extends over the 
edge onto the lower side. In some sporophores it is very 
