The role of micro-organisms in the inducing nature of the
casing layer was also studied by replacing the non-sterile
casing layer by activated charcoal, a chemical absorbent, or by
a sterilized casing layer. Whereas fruiting was inhibited or
delayed on a sterile casing layer, normal fruiting appeared on
activated charcoal. This suggests that the micro-organisms in
the casing layer remove one or more inhibitory compounds of
fruiting produced by the mushroom mycelium rather than that
they produce fruiting inducing substances (Eger, 1961 ; Long
& Jacobs, 1974 ; Wood, 1984).