Dec. 10, 1913 
Polyporus Dryadeus 
247 
the trees bearing sporophores were apparently in a healthy condition, 
yet an examination of the root system showed in every case one or more 
large roots completely rotted Two stumps of Quercus alba were found 
with sporophores of Polyporus dryadeus springing from the rotted roots. 
In no instance were trees which were attacked by this fungus found in 
groups or even adjacent to each other The majority of the trees with 
this disease in their roots were growing under unfavorable environments. 
The boles of some of them were also attacked by various heart-rotting 
fungi, while others were perfectly sound above the collar, although they 
bore sporophores of P. dryadeus at the ground line. 
No rhizomorphs of any kind were found associated with this rot, 
either beneath the bark, on the surface of the roots, or ramifying in the 
adjacent soil. How the lower part of the smaller roots became infected 
is not known. 
The identity of the fungus causing this root-rot with the European 
fungus known as Polyporus dryadeus may be questioned. Through the 
courtesy of the officials in charge, the writer was permitted to examine 
all the American and European specimens of P. dryadeus in the fol¬ 
lowing herbaria: 
Pathological and Mycological Collections of the Department of Agri¬ 
culture, at Washington, D. C., Herbarium of the New York Botanical 
Garden, and the Cryptogamic Herbarium of Harvard University. 
Authentic specimens of Polyporus dryadeus from America, England, 
France, Germany, and Austria were examined, and a careful comparison 
of each with the material used as the basis of this article showed that the 
American plant under discussion is undoubtedly identical with the Euro¬ 
pean fungus known as P. dryadeus . 
There are three collections in the laboratory of the Office of Investi¬ 
gations in Forest Pathology, at Washington, D. C., of a Polyporus on 
Tsuga heterophylla from three widely separated localities in the State of 
Washington. These specimens were collected by C. J. Humphrey, of 
this office, and the legends accompanying them indicate that the sporo¬ 
phores were attached to the host at or near the surface of the ground 
and that the plant is a true parasite that kills the trees it attacks. 
These specimens agree in all essential characters, both gross and micro¬ 
scopic, with Polyporus dryadeus , and although the writer has not seen 
the rot produced in this host, he believes the fungus is this plant. 
SUMMARY 
(1) Polyporus dryadeus is a root parasite of the oak, producing a white 
sap rot and a heart rot in the roots. 
(2) In all the trees examined this rot did not extend upward into the 
tree as a true heart or sap rot of the trunk, but was limited to the under¬ 
ground parts of the tree. 
