The Canher of the Larch. 
303 
especially single trees in mixed plantations are less subject to 
attack. 
Attention is generally in the first instance directed to the 
disease by the flattened and deformed portions of the stem, the 
free exudations of resin, and the discoloration of the bark as if 
covered with soot. This blackening on the bark is due to the 
presence of a small fungus (^Anteimarid i^ithiiophUa, Nees), which 
is found on the bark of several other conifers besides the larch. It 
has the appearance to the naked eye of a covering of soot, and 
its true nature therefore escapes the notice of any but a careful 
observer. 
At certain times the surface of the depressed portion produces 
many minute whitish cup-shaped fungi, the interior of the cup 
presenting a reddish-orange colour. The fungus generally takes 
possession of a tree in more than one place ; indeed, when a 
plantation is seriously affected, the fungus can be seen on all 
parts of the trees, even on the youngest branches. 
The cup-shaped fungus on the bark is the only part of the 
parasite that can be distinguished by the naked eye. This is 
the fruiting part, pushed out from the roots (mycelium), wliich 
are in full possession of the subjacent bark, in order to ripen 
and shed its seeds in the air. This fungus is tlie true cause of 
the canker, as Sir W. C. Trevelyan suggested. It is a parasite 
sending its innumerable minute rootlets into the living bark, 
and taking possession of the nutritive juices which the plant 
prepares for its own use. The fungus lives in the bark ; every- 
where throughout the cankered portions the bark is completely 
permeated by its mycelium, consisting of extremely minute 
branching threads, wliich, by abstracting all available nourish- 
ment from the bark, kills it. Further, it feeds on the active 
layer below the bark from which the new wood and bark are to 
be formed, and destroys it so that it is unable to perform its 
functions. Even after this cambium layer has begun its work 
of actively forming new wood, the mycelium spreading in the 
bark above gradually arrests its formation. 
As the fungus grows year after year, the mycelium extends 
itself in search of food into a fresh portion of the bark, and 
so the further formation of wood is prevented, and an ever- 
increasing area of depression of the trunk is produced. 
In Fig. ] the ordinary form of the stem is seen at the two 
extremities, and the fiattening caused by the canker in the 
centre. The origin of the injury was at a point slightly to the 
left of the branch, which has at length been killed by the fungus. 
The mycelium has spread outwards, growing more rapidly up 
and down the stem, causing an elongated canker. The tree 
