Nov. 10,1913 
Heart-Rots of Hardwood Trees 
125 
but from the above record it also occurs on chestnut and on ash, while 
Dr. Weir, of the Office of Investigations in Forest Pathology, reports 
it on larch in 1913. 
From the studies made in the field the writer finds no proof of the 
ability of this fungus to grow permanently as a saprophyte in humus 
and decayed forest litter. All sporophores seen certainly grew from 
mycelium inside the living, diseased trees at whose base they were 
found and not from mycelium ramifying in and drawing nourishment 
from the soil or leaf litter. 
Weir reports 1 the finding of sporophores of Polyporus berkeleyi 
attached to the roots of the larch in Montana, but from observations 
made in that region reached the conclusion that the mycelium ramified 
in the deep forest litter and drew its food from that source as well as 
from the rotten roots to which the sporophores were attached. It will 
prove very interesting if this rot in the larch should prove to be similar 
to that produced by this fungus in the oak, especially since the anatom¬ 
ical character of the wood of these trees is so different. 
A STRAW-COEORED ROT OF OAKS CAUSED BY POEYPORUS FRONDOSUS 
The initial stage of the straw-colored rot of the white oak (Quercus 
alba) is characterized by the dissolution of the middle lamellae and the 
delignification of some of the wood fibers, leaving the fibers now con¬ 
sisting of cellulose free from each other. (PI. VIII, fig. 4.) The advanc¬ 
ing line of the rot upward in the tree consists of irregular, rather indefinite 
white patches, conforming more or less in size and shape to the largest 
medullary rays, or of narrow white bands projecting into the sound 
wood. Five or six inches below the boundary line between the advanc¬ 
ing rot and sound wood the color in radial sections is more evenly white, 
as the patches have coalesced more or less at this stage. The unpolished 
split surface feels velvety, owing to numerous projecting free ends of 
the cellulose fibers. A tangential view of the advancing line of rot 
shows a whitish surface consisting of white delignified fibers interspersed 
with unchanged medullary rays and unchanged or only partially deligni^ 
fied vessels and their immediate adjacent tissue. In cross section the 
rot has a whitish cast surrounded by the natural color of sound heart- 
wood. 
The amount of delignified tissues in the earlier stages of this rot is 
much less than that found in the earlier stages of the string and ray 
rot. Eight to twelve inches behind the advancing point of the rot numer¬ 
ous colorless hyphae are found in the larger vessels. At this stage 
in the rot some of the delignified tissue has been entirely absorbed. 
The delignification and absorption begin with the inner layer of the 
wood fibers and proceed centrifugally, so that the lumen of the cell 
1 Weir, J. R. Some observations on Polyporus berkeleyi. Phytopathology, v. 3, no. 2, p. 101-103, pi. 9, 
1913. 
