SOME FUNGI IN WOOD. 47
mostly along the rays the hyphae spread into the cells of the wood.
Black layers, which consist entirely of hyphae, now appear in the
wood, and the walls, thanks to the spread of these hypha-, now
become delignified and the wood takes a yellowish brown tint and
is much too weak for use; a good deal of resin exudes from the
attacked tree, which, of course, dies, while the fungus continues
its activities until the wood becomes too dry. Thanks to its
rhizomorphs Armillaria can spread through the soil for a con-
siderable distance, and by this means neighbouring trees may
fall victims.
Among the Thellephoraceae, of which Coniophora has already
been considered, several species of Stereum are destructive to
wood.
Stereum spadiceum Fr., is a well known species, common
enough in Britain, and occurring especially on oak and ash. In
the former tree at least, it causes, together with some closely
related species, a piped rot in the heartwood. The rot is yellowish
white, and occurs in small branches, from which it spreads into
the trunk, producing dark brown streaks—incipient decay; in
these appear yellowish bands which finally coalesce to produce a
pale coloured rotted residue. In the felled timber it attacks the
sapwood, but not the heartwood, although apparently it will
continue its growth if present in the living tree.
Stereum frustulosum (Pers.) Fr., causes another white rot
mainly in heartwood, and is found in oak and beech, although
in this country it is rare. Incipient stages are marked by a dark
brown discoloration, and as decay proceeds there appear white
fusiform patches of varying size, in which the wood disintegrates:
the holes, which are areas where the wood has broken down, are
lined with the hyphae of the fungus, and they gradually enlarge,
although they never coalesce. The fungus is a wound parasite
which enters the heartwood when it becomes exposed by the
breaking of branches. While decay can continue after the tree
is felled, there seems little doubt that only standing trees are
infected. The rot is often described as "partridge wood."
Stereum hirsutum (Willd.) Fr., a common and widespread
species, is found on felled wood and dead branches of a number
of broadleaved trees such as oak, birch, poplar and beech, and
also on stumps. It produces a white rot of the sapwood, the wood
becoming soft but rather fibrous, yellowish white and lighter in