reus, on oak
stump. Entirely sulphur-yellow (1/6 natural size). Copyright.]

The tubes are small, and the walls thin and delicate, and are sometimes
much torn, lacerated, and irregular. When the mycelium has grown in the
interior of a log for a number of years it tends to grow in sheets along
the line of the medullary rays of the wood or across in concentric
layers corresponding to the summer wood. Also as the wood becomes more
decomposed, cracks and rifts appear along these same lines. The mycelium
then grows in abundance in these rifts and forms broad and extensive
sheets which resemble somewhat chamois skin and is called "punk."
Similar punk is sometimes formed in conifers from the mycelium of _Fomes
pinicola_.

[Illustration: PLATE 70, FIGURE 185.--Polyporus sulphureus. Caps joined
in a massive tubercle (1/2 natural size).]

_Polyporus sulphureus_ has long been known as an edible fungus, but from
its rather firm and fibrous texture it requires a different preparation
from the fleshy fungi to prepare it for the table, and this may be one
reason why it is not employed more frequently as an article of food. It
is common enough during the summer and especially during the autumn to
provide this kind of food in considerable quantities.

[Illustration: PLATE 71, FIGURE 186.--Polyporus brumalis. Cap and stem
brown, tubes white. Lower three plants natural size, upper one enlarged
twice natural size. Copyright.]

=Polyporus brumalis= (Pers.) Fr.--This pretty plant is found at all
seasons of the year, and from its frequency during the winter was named
_brumalis_, from _bruma_, which means winter. It grows on sticks and
branches, or on trunks. It usually occurs singly, sometimes two or three
close together. The plants are 3--6 cm. high, the cap 2--6 cm. in
diameter, and the stem is 3--6 mm. in thickness.

The =cap= is convex, then plane, and sometimes depressed at the center
or umbilicate. When young it is somewhat fleshy and pliant, then it
becomes tough, coriaceous, and hard when dry. During wet weather it
becomes pliant again. Being hard and firm, and tough, it preserves long
after mature, so that it may be found at any season of the year. The cap
is smoky in color, varying in shade, sometimes very dark, almost black,
and other specimens being quite light in color. The surface is hairy and
the margin is often fimbriate with coarse hairs. The =stem= is lighter,
hairy or strigose. The =tubes= are first white, then become