on every thread of
mycelium leading to it, and all the mushrooms, present and to come, that
are attached to this arrested web of mycelium are affected by the poison
of the decaying old mushroom stump, and fogg off. Any impure matter in
the bed with which the mycelium comes in contact will destroy the spawn
and fogg off the young mushrooms. Lachaume complains about the larvae of
two beetles, namely _Aphodius fimetarius_ and _Dermestes tessellatus_,
which "cause great damage by eating the spawn, thereby breaking up the
reproductive filaments." Damage of this sort by these or any other
insect vermin will cause fogging off. But I have not noticed either of
the above beetles or their larvae about our beds.

=Flock.=--This is the worst of all mushroom diseases and common wherever
mushrooms are grown artificially. It is not a new disease; I have known
it for twenty-five years, and it was as common then as it is now, and
practical gardeners have always called it _Flock_. I say "worst of all
diseases" because _I know_ that mushrooms affected by it are both
unwholesome and indigestible, and I can readily believe that in
aggravated cases they are poisonous. It is caused by other fungi which
infest the gills and frills of the mushrooms, and render them a hard,
flocky mass; sometimes the affected mushrooms preserve their white skin,
color, and normal form, at other times the cap becomes more or less
distorted. The illustration, Fig. 26, is from life, and a good average
of a flock-infested mushroom. In gathering mushrooms the growers should
insist that every flock-infested mushroom be discarded, and consumers of
mushrooms should familiarize themselves with this disease so as to know
and reject every mushroom showing a trace of it.

[Illustration: FIG. 26. A FLOCK-DISEASED MUSHROOM.]

Flock does not affect all the mushrooms in a bed at any time, and I do
not believe it spreads in the bed, or, to use the expression, becomes
contagious. If one spot of mildew appears upon a cucumber, rose, or
grape vine indoors, and is not checked, it soon becomes general all over
the plant or plants, and if one spot of mold occurs in a propagating bed
and is not checked at once it soon spreads over a large space and
destroys every cutting or seedling within its reach, but this is not the
case with flock in a mushroom bed. If one mushroom is affected with
flock every mushroom produced from that piece of spawn is affected, but
not one mushroom produced