Dec. 6, 1915 
Honeycomb Heart-Rot of Oaks 
423 
There is a brownish discoloration of the heartwood on the outer edges 
of the affected area. This character is also common to several other 
heart-rotting fungi. 
When a living tree having the rot caused by 5 . svhpileatum is first 
split open, there is a very distinct odor of old honeycomb. In some 
white oaks the old pockets have blackish deposits on the walls which 
make this rot resemble even more strongly an old, blackened honeycomb. 
MICROSCOPIC CHARACTERS 
A microscopic examination of the diseased wood in the initial stage 
of a pocket shows small groups of partially delignified wood fibers scat¬ 
tered in the neighborhood of the large vessels. Delignification in these 
wood fibers begins with the inner layer or the tertiary lamella of each 
fiber and proceeds outward toward the primary or middle lamella. The 
middle lamella is then attacked and rapidly dissolved, thus freeing each 
cell from its neighbor. 
The walls of the small medullary rays are more slowly delignified than 
the wood fibers, while the walls of the large vessels resist delignification 
much longer than either the wood fibers or small medullary rays. The 
tyloses in the large vessels are the last to be delignified. They contain 
many small, irregular holes, apparently made by the passage of fungus 
hyphae through them. Delignification is not very pronounced in the 
cells of the radially placed rows of small vessels of the summer wood. 
The pits of the vessels and the cells do not seem to be enlarged by the 
action of the fungus until the last stages are reached, if at all. 
FUNGOUS MYCELIUM 
In the earliest stages of the rot the enzyms seem to precede the fungous 
hyphae, especially in the region of the wood fibers. In the larger vessels 
a few colorless very small hyphae can be seen in the region adjacent to the 
area first delignified. As delignification advances, the threads in the 
vessels increase in number, and during the period of cellulose absorption 
the vessel from which the delignification started often becomes stuffed 
with small, intricately branched, colorless hyphae. 
In the center of the pockets are often seen small, white, threadlike 
bodies. On examination these prove to be (1) the remnants of the 
delignified walls of the vessels and especially of the tyloses, which often 
persist even after all of the walls of the vessels have been absorbed, and 
(2) fungous tissue, which is composed of large (10/x), longitudinal, hyaline, 
thin-walled hyphae and many smaller hyphae, all interwoven into a rodlike 
mass. 
In many of the pockets where much of the cellulose has been absorbed, 
dense white fluffy masses of mycelium either nearly fill or in some instances 
only line the cavities. This mycelium is composed of small, branched, 
colorless, thick-walled hyphae, some of which have granular or tuberculate 
walls. If the pockets border on checks or windshakes, the fluffy masses 
of mycelium are a reddish brown in place of white and often form a more 
