38
THE ESSEX NATURALIST.
doubt as to the manner in which the fungus enters the tree;
it probably enters through dead roots, and there is no evidence
that it can enter through the branches as in the preceding species.
The sporophores often occur at some distance from the tree,
although, of course, they are attached to the roots; they occur
less commonly on the trunk up to 10 or 12 ft. [18], usually
occupying the latter position in fallen trees which have com-
pletely rotted. In incipient stages of decay the heartwood has
a rather deeper colour than usual: in typical stages the wood
is split into cubical pieces, at first yellowish or pale brown, and
finally reddish brown; masses of white hyphae till the clefts, often
mixed with resin, and the wood becomes soft, dry and friable.
Associated with the rot is a smell which Hartig claims is reminis-
cent of turpentine, although not identical with it.
Polyporus dryadeus (Pers.) Fr., produces a butt rot in oaks;
Smith [30] gives Beech as another host. The rot is localised at
the base of the tree and is usually confined to the heartwood,
where incipient decay is marked by a darker colour ; Hubert [20]
states that it is a rot of the roots of oak and chestnut, characterised
by being confined to the underground parts of the tree. Advanced
decay begins with the appearance of elongated yellow or whitish
pockets, where the cell walls have been broken by the fungus,
and these areas increase in size until they meet, when the heart-
wood is reduced to a soft, somewhat fibrous mass often interspersed
with sheets of white mycelium. Like the last mentioned species
the decay produced results in a considerable weakening of the
base of the tree, so that it is more liable to be thrown by wind
than is a sound tree.
Polyporus spp. Certain other species of this large genus of
fungi must receive briefer treatment. The well known Birch
Polypore (P. betulinus (Bull.) Fr.), attacks birches, and starts
its development in the sapwood, spreading throughout the
heartwood, and also attacking the phloem. There is no visible
change in the wood in the early stages of the rot, but in advanced
decay it develops a yellowish or pale brown colour, and breaks
into large cubes, separated by thin masses of white mycelium;
such wood powders with ease. P. borealis Fr. (= Daedalea
borealis (Wahlenb.) Quel.), occurs on spruce, producing a white
rot of the cubical type, while P. squamosus (Huds.) Fr., is res-
ponsible for a white rot in several broad-leaved trees. P.