SOME FUNGI IN WOOD.
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hispidus (Bull.) Fr., is described by Tubeuf [32] as causing in
wood a brown discoloration, which is marked out into squares
by short white lines, which run radially and vertically: it occurs
on a number of trees and is common in ash. P. adustus (Willd.)
Fr., causes a mottled or cubical white rot in the sapwood of
felled oak, and is also found on beech, ash and other broad-
leaved trees.
Like Polyporus, the related genus Fomes includes numerous
species destructive to wood.
Fomes annosus (Fr.) Cooke, is a familar species; Hartig,
who refers to it as Trametes radiciperda, describes it as
"undoubtedly the most dangerous of all the parasites met with
in coniferous woods." It is catholic in its choice of hosts, and
in Britain is found on many conifers: Eades [9] says that any
conifers may be affected to a certain extent. Its activities are
confined to the roots and base of the trunk, and result in a white
pocket rot, although the disease is sometimes referred to as red
rot because of the brown or reddish-brown discoloration
associated with the earlier stages of decay; during this stage a
gum is formed, probably as a result of the breakdown of the
cell walls, and this gum forms a zone around the decayed region
and effectively prevents lateral spread of the hyphae; as a
consequence the decayed zones are conical, spreading up from
the roots; there may be a number of such cones in the butt
of the tree. Another type of attack takes the form of a hollow
cylinder or cone around a central peg of sound tissue. As decay
proceeds a good deal of resin is exuded, and small white elongated
pockets are formed, often with a black spot in the centre; these
pits may become very abundant in advanced decay, when the
wood becomes light and dry, easily crumbling in the hand:
finally it may reach a stage where it resembles sawdust. The
fungus enters the tree by the roots.
Fomes igniarius (Linn.) Fr., is met with in many broad-leaved
trees such as ash, beech and birch. Like the last species it also
causes a white rot in the host tree; the incipient stages are
marked by a brown discoloration; in the advanced stages the
wood assumes a yellowish white colour and becomes light and soft.
Hartig refers to this fungus as causing the commonest kind of
white rot in oak, although Cartwright and Findlay [8] state that it
is extremely rare, if it occurs at all, on this tree.