246 OVERHOLTS: DIAGNOSES OF AMERICAN Portas—II 
P. corticola is a soft white species (PLATE 13, FIGS. I, 2) that 
appears to be fairly common from New York to the Rocky 
Mountains. Egeland (Norsk. res. Poresv. p. 143) reports it as 
occurring chiefly on aspen and birch in Norway. My records — 
show Acer (including A. Negundo) to be its common host though 
found on both Populus tremuloides and P. trichocarpa. In the 
Ohio Valley it seems to frequent the beech. Sometimes it is 
strictly a bark-inhabiting fungus but just as frequently it grows 
on decorticated wood, particularly wood in advanced stages of 
decay—a fact that is responsible for the lack of information in 
many collections as to the exact substratum. 
. Porta corticora (Fr.) Cooke. A, Hyphae showing cross walls 
and abeanee of clamp connections; B, Spores, some characteristically ag- 
glutinated in groups. 
As here interpreted the species is, in its microscopic characters, 
quite a variable one. Our American plant differs so markedly 
in the matter of cystidia that it might well be held to be at least 
aseparate variety. In the European specimens I have examined 
and as reported by Egeland (Norsk. res. Poresv. p. 143), con- 
spicuous cystidia are present in the hymenium. PLATE 13, 
FIGS. 3, 4, show these bodies as. seen in plants from Sweden. 
Egeland also reports, and I have verified his statement in my 
study of Swedish specimens, that other bodies, which he terms 
paraphyses, with capitate-incrusted apices, are present with the 
cystidia, and in fact in some specimens I find this to be about the 
only. cystidium-like organ present. In American collections the 
type of cystidium that approaches nearest to the well-developed 
form in European specimens is shown in PLATE t3; Fic. 5, 
made from a Pennsylvania collection taken in 1920, though 
they have been seen occasionally in another collection from 
Ohio. More frequently the capitate-incrusted type is present, 
