SOME COMMON MUSHROOMS AND HOW TO KNOW THEM 49 
This fungus is of wide distribution and of common occurrence, appearing 
on logs and trunks. It is easily recognized by the brittle varnished crust of 
the cap and stem. 
POLYPORUS 
Species belonging to the genus Polyporus present considerable 
variation in stem, form, and texture. The stem may be central, 
excentric, or absent; the hymenophore circular, reniform, or hoof 
shaped, azonate or grooved; and the substance fleshy, soft, corky, 
or woody. This genus is distinguished from Polystictus by the 
thicker cap and from Fomes by the nonstratose tubes. 
Species of this genus are widely distributed, and representatives 
may be found from the extreme North to the Tropics. Polyporus 
contains a few edible species and many wound parasites, species 
injurious to economic and ornamental trees. Wound parasites are 
fungi that gain entrance to the interior of a tree or host through 
some unprotected surface resulting from injury by lightning, insect 
attack, injudicious pruning, or some other agency. 
POLYPORUS BETULINUS. BIRCH POLYPORUS 
In the birch polypore the hymenophore is tough and fleshy, then corky, hoof 
shaped, umbonate at point of attachment, margin thickened, obtuse incurved, 
white when young, later light to dark mottled gray, zoneless, smooth; the 
pores are minute, short, unequal, whitish. 
The fungus is of Common occurrence on birch trees, Measuring from 3 to 8 
inches or more in width. When young it is considered edible, but is tough 
and possesses a rather strong flavor. It is often used as material for outdoor 
sketching, for which purpose it is very well adapted. 
POLYPORUS FRONDOSUS 
This species occurs in large tufts, which measure 6 inches to over a foot 
in breadth. The caps are very humerous, crowded and overlapping, 1 to 
2 inches in diameter, irregular in shape, curved, repand, lobed or cleft, brown 
or sooty gray; the stems are indefinite, branching or ccnfluent; the pores are 
very small, white. 
This is a very common plant, growing about stumps, roots, and trunks. It is 
edible and tender when young, but soon becomes tough. 
POLYPORUS SULPHUREUS. SULPHUR POLYPORUS 
This is a very conspicuous fungus on account of its large clusters and the 
characteristic sulphur-yellow color. The caps are fleshy, spongy, attached lat- 
erally, very much imbricated, more or less fan shaped, smooth, even when 
young, later ridged and furrowed; margin at first thick and blunt, becoming 
thinner; the pores are very small, plane and sulphur yellow. 
Polyporus sulphureus occurs abundantly and is edible, though of doubtful 
value. It is of interest as a wound parasite on various trees, gaining entrance 
to the interior of a tree through an exposed surface and finally causing the 
death of the host. This is a very striking plant on account of the bright sul- 
phur-yellow color, which quickly attracts the attention of the collector. 
POLYSTICTUS 
Species of the genus Polystictus may be differentiated from those of 
Polyporus because of being thinner with caps more pliant. None 
are to be especially recommended for table purposes, but by their 
abundance and attractiveness they force themselves upon the atten- 
tion of the amateur or nature student. The species described here 
are all sessile and shelving. 
