Dec. io, 1913 
Polyporus Dryadeus 
241 
Maine. In the Cryptogamic Herbarium of Harvard University there is 
a collection on PopuLus grandidentata Michx. from New Hampshire, while 
in the laboratory of forest pathology of the Department of Agriculture at 
Washington, D. C., there is a fine collection on Populus tremuloides Michx. 
from near Steamboat Springs, Colo. (Hedgcock, 1913). 
This fungus on Populus agrees in all essential characters with the form 
of Polyporus dryophilus found on oak. The sporophores are, however, 
somewhat smaller than those usually found on oak and approach the 
applanate type. (PI. XXI, fig. 7.) The hard granular core is always 
present, but is formed between the sap wood and bark (PI. XXI, fig. 8), 
as the fungus is able to rot the sapwood as well as the heart of this host. 
It therefore does not have to depend on branch holes or other openings 
through the sapwood in order to form its sporophores, as it does in the 
oak. 
Through the kindness of Von Tubeuf the writer obtained a European 
specimen of Hartig’s so-called rot of Polyporus dryadeus in oaks. (PI. 
XXII, fig. i.) 1 It is unquestionably the rot produced by P. dryophilus . 
(PI. XXII, fig. 3.) 
The following discussion of the rot caused by Polyporus dryadeus 
embodies the results obtained from extensive field studies made in 
the forests of Arkansas, eastern Texas, Oklahoma, Maryland, and 
Virginia. 
The sporophores of P. dryadeus are always found at or very near 
the ground at the base of the host. This first suggested to the writer 
that the fungus might be a true root-rotting organism. Trees with 
sporophores at their bases and wind-thrown oaks with and without 
the sporophores attached were carefully studied. Sections of the 
trees were cut, roots dug up and examined, and every effort made to 
determine exactly the character of the rot produced. The roots and 
stools of 20 trees attacked by this disease were examined, and sections 
of the various stages of the rot were studied. 
The microscopic characters of the rot from each tree were found to 
be identical, although of the 20 trees examined 5 were in Arkansas, 
3 in Texas, 2 in Oklahoma, 4 in Maryland, and 6 in Virginia. In every 
instance the trees were found to have a white rot which attacks first 
the sap and finally the heartwood of the roots. The rot originates in 
the lower portion of the roots and spreads in them toward the base of 
the tree. 
The first evidence of the disease is a reddish brown discoloration of 
the inner bark and cambium. If the diseased roots are exposed in a 
damp chamber at this stage, white floccose spots of mycelium will 
appear on the outside of the bark, but the rot has not yet become 
evident in the wood. As the rot progresses, discolored, watery, reddish 
1 Figure i on Plate XXII was made from a photograph of a piece of the original type material used by 
Hartig in his description of the rot of Polyporus dryadeus (1878). 
