A DISEASE OF TILE BLACK LOCUST. 23 
allied honey locust ( Gleditschia triacanthos). Between the 
ducts the thick-walled short wood fibres are massed closely 
together with here and there a group of wood parenchyma 
cells. ‘The medullary rays are numerous, and many extend 
continuously out to the sapwood.’ They are rather obscure 
when viewed with the naked eye. 
The changes which the mycelium of Polyporus rimosus 
brings about in the locust wood are very striking. The 
hard resistant wood is transformed into a soft yellow mass 
which, when wet, is more or less spongy. The almost flint- 
like character of the sound wood is wholly gone in com- 
pletely decayed wood, which can be cut almost like cheese. 
On Plate 1 a cross-section of a locust trunk is shown in 
which parts of the heartwood are destroyed. The tree 
from which this section was taken measured 9 inches in 
diameter at this point. A sporophore grew 20 feet from 
the ground, and the decay extended up the trunk from this 
point for 3 feet, and down the trunk 8 feet 5 inches. It 
will be noted that the central part of the heartwood is com- 
pletely rotted, and that the decay extends outward in radial 
lines. When split longitudinally it will be seen that these 
radial lines form the edges of sheets of decayed wood which 
are from 1 to 2 inches in width vertically; they occur 
every few inches in the vertical section, and extend out 
from the central decayed mass toward the bark, which they 
reach in many cases. Every one of these sheets of decayed 
wood has a more or less distinct red core almost the 
size of asmall lead pencil, composed of wholly disintegrated 
wood held together by the mycelium of the fungus; the 
whole core can be lifted out intact. Extending upward 
and downward from this core the yellowish-brown wood is 
- discolored, becoming yellow orange * nearest the core and 
very light straw color farther away. As the cores grow 
outward, the hyphae composing them grow through the 
* See yellow orange shade No. 1, Milton Bradley color scale. 
