MurriL_t: PoLyporacEAE oF NortH AMERICA 425 
It is chiefly distinguished from nearly related genera by its separ- 
able hymenium, which, upon investigation, is found to be cut off 
from the context proper by a thin flesh-colored layer of mycelium 
connected very loosely with the adjacent layers and allowing them 
to separate easily. In age this layer disintegrates and the tubes 
fall away in irregular masses, leaving the smooth white surface of 
the context conspicuously exposed. 
Piproporus SUBEROSUS (L.) Murrill 
Boletus suberosus L. Sp. Pl. 1176. 1753. 
Boletus betulinus Bull. Herb. France, p/. 372. 1786. 
Polyporus betulinus Fr. Syst. Myc. 1: 358. 1821. 
Piptoporus betulinus Karst. Rev. Myc. 3: 17. 1881. 
Liptoporus suberosus Murrill, Jour. Myc. 9: 94. 1903. 
Pileus fleshy to corky, compressed ungulate, convex above, 
plane below, attached by a short umbo behind, varying to bell- 
shaped when hanging from horizontal trunks, 5-30 x 5-20 x 2-5 
cm. ; surface smoky, covered with a thin separating pellicle, gla- 
brous, devoid of markings, cracking with age; margin velvety, 
concolorous, obtuse, projecting beyond the hymenium nearly a 
centimeter: context fleshy-tough, elastic, homogeneous, 3 cm. 
thick, milk white; tubes separated from context by a thin pink 
layer, 0.5 cm. long, 2-3 toa mm., sodden white ; mouths very 
irregular, dissepiments thicker than pores, obtuse, entire, crumb- 
ling away in age, leaving the smooth white context : spores white, 
cylindrical, curved, 4~5 y in length. 
This plant is confined to species of birch, upon the dead or decay- 
ing trunks of which it is quite abundant in the northern United 
States and Canada. Its common occurence in Sweden explains why 
it was noticed and described by Linnaeus in Flora Suecica as early 
as 1745. From the following selected exsiccati it will be seen 
that this species is as cosmopolitan as its hosts. France, Roume- 
guére 2102; Germany, Sydow 627; Saxony, Arieger 907; 
Sweden, Romell ro, Murrill; Russia, Jaczewski 76 ; Wisconsin, 
Baker ; New Jersey, Murrill; New York, Underwood, Murrill; 
New Hampshire, Afss Minus, Grout. 
ScuTIGER Paul. Icon. Champ. f/. 37. f. 1-3. 1793 
Seven species were included in this genus by Paulet, one of 
them an agaric, four hydnums and two polypores. The first species 
