that have been permitted to rot and fall out. Surface wounds allowed
to decay will deepen in course of time and produce cavities.
Cavities in trees are especially susceptible to the attack of
disease because, in a cavity, there is bound to exist an
accumulation of moisture. With this, there is also considerable
darkness and protection from wind and cold, and these are all ideal
conditions for the development of disease.

The successful application of a remedy, in all cavity treatment,
hinges on this principal condition--_that all traces of disease
shall be entirely eliminated before treatment is commenced_.

Fungous diseases attacking a cavity produce a mass of fibers, known
as the "mycelium," that penetrate the body of the tree or limb on
which the cavity is located. In eliminating disease from a cavity,
it is, therefore, essential to go _beyond_ the mere decaying surface
and to cut out all fungous fibers that radiate into the interior of
the tree. Where these fibers have penetrated so deeply that it
becomes impossible to remove every one of them, the tree or limb
thus affected had better be cut down. (Fig. 118.) The presence of
the mycelium in wood tissue can readily be told by the discolored
and disintegrated appearance of the wood.

The filling in a cavity, moreover, should serve to prevent the
accumulation of water and, where a cavity is perpendicular and so
located that the water can be drained off without the filling, the
latter should be avoided and the cavity should merely be cleaned out
and tarred. (Fig. 116.) Where the disease can be entirely
eliminated, where the cavity is not too large, and where a filling
will serve the practical purpose of preventing the accumulation of