122 
Journal of Agricultural Research 
Vol. I, No. 2 
therefore, can enter the tree through fire scars in the butt and also 
through broken branches or other wounds on the bole and in the top of 
the tree. There is also a honeycomb rot in oak and in chestnut caused 
by a species of Stereum. This honeycomb rot in its earlier stages resem¬ 
bles so closely certain stages of the rot caused by P. pilotae that it is 
very difficult to determine which fungus produced the rot, unless the 
sporophores are present. 
A STRING AND RAY ROT OF OAKS CAUSED BY POEYPORUS BERKELEYI 
The inittel stage of the string and ray rot in the white oak when seen 
in a radial longitudinal section is characterized by the presence of large 
amounts of cellulose tissue, causing the rotted wood to have a yellowish 
white appearance. This stage of the rot may extend for 4 to 8 inches 
longitudinally, when it terminates rather abruptly in apparently sound 
wood. The cellulose tissue is composed exclusively of delignified wood 
fibers, which constitute the bulk of the summer wood. The middle 
lamellae have entirely disappeared, so that each delignified wood fiber is 
separate from its neighbor. 
The next stage of the rot is the rather rapid and complete absorption of 
these delignified fibers, leaving both the spring and summer vessels, the 
cells immediately adjacent, and the medullary rays intact. The rot at this 
stage is most characteristic, consisting of a rather dry mass of medullary 
rays interwoven with long, flat strings of wood (PI. VIII, fig. 2). These 
strings are sometimes 8 to 10 inches long by one-sixteenth of an inch 
wide and consist of the vessels held together by the unabsorbed adjacent 
cells. The rot in this stage is reddish brown and on account of its peculiar 
and characteristic structure has been named the “string and ray rot” 
by the writer. This second stage of the rot may extend from a few 
inches to several feet up the tree. At first the flattened strings of wood 
are rather tough, but this gives place to a condition in which the strings 
get brittle and can be crumbled between the fingers into a brownish, 
coarse powder. Finally the entire mass of rotting wood becomes over¬ 
run with a colorless mycelium. In this condition the rot is very moist, 
almost wet, and consists of fragments of vessels and of the medullary 
rays, interwoven with the colorless hyphae of the fungus. It can now 
be compressed with the hands into rather firm balls which may be thrown 
with force and yet will not break into pieces. 
Finally the entire mass of rotted wood and mycelium gradually disap¬ 
pears till a hollow is left in the base of the tree. Over the surface of this 
vanishing mass brittle white or creamy white layers of mycelium are 
formed, on the undersides of which are cottony masses. Shakes, checks, 
or worm holes in the wood may have a slight mycelial felt in them. 
The string and ray rot seems to be one of the very few heart-rots of the 
white oak capable of the complete absorption of the heartwood of the 
tree, thereby producing hollows. The slow rate of travel upward in the 
