48 THE ESSEX NATURALIST.
weight than normal. It is also recorded that S. hirsutum can
attack the heartwood, which it reaches from the dead branches
on which it is growing, and here it produces a piped rot, and
finally the whole wood may become of a yellowish colour.
Among other species of the genus Stereum may be mentioned
S. rugosum (Pers.) Fr., which is responsible for a white piped
rot in oak, and S, sanguinolentum (A. and S.) Fr., a species found
especially in coniferous wood and producing a white pocket rot.
Hymenochaete and Peniophora: Several species of these genera
are known to be wood rotting forms; thus H. rubiginosa (Dicks.)
Lev., according to Brown [2] produces a white pocket rot in dead
oaks and chestnuts, while P. gigantea (Fr.) Mass., occurs on dead
coniferous wood and on prepared timber.
Among the Hydnaceae mention may be made of Hydnum
and Irpex. Hydnum erinaceus (Bull.) Fr., occurs on many broad-
leaved trees, producing a white rot in which the wood is soft and
spongy; finally large cavities appear in the heartwood, which
becomes filled with yellowish mycelium. Hubert [20] says that
it occurs in oaks in the central and southern hardwood regions
of the United States, while Cartwright and Findlay [8] state
that in Britain it has usually been found on beech.
Hydnum diversidens Fr., is also said to produce a white rot in
oak and beech; infection is through wounds and the mycelial
masses associated with advanced decay are white.
Irpex obliquus (Schrad.) Fr., is found in felled wood. Cart-
wright and Findlay [8] say that it attacks the smaller dead
branches and to a less extent the sapwood of felled oak, producing
a soft white mass of decayed wood.
Turning now to the Ascomycetes, we find that as far as the
rotting of wood is concerned, few species and genera are of
economic importance. Among such mention may be made of
Xylaria: a root rot of various hardwood trees, and especially
apple, has been attributed to X, hypoxylon, Grev., and X.
polymorpha, Grev.; the wood of the root and butt becomes
soft and finally white and spongy and easily crushed, while
throughout the rotten areas there are numerous thin blackish
" zone " lines, rather like pencil marks. Hubert [20] reports
that Hypoxylon coccineum Bull., produces white pockets of rot,
especially in beech, and is sometimes found on various hardwood
products, while Ustulina vulgaris, which occurs on beech