Introduction to Fungi, Third Edition

522 HOMOBASIDIOMYCETES
agar media, only the thinner hyphae seem to
give rise to vegetative growth (Borriss, 1934).
19.2.3 Types of lamellae
The gills of most lamellate fruit bodies are
wedge-shaped in longitudinal section and are of
the aequi-hymenial (aequi-hymeniiferous) type.
This term refers to the fact that the hymenium
develops in an equal manner all over the surface
of the gill, i.e. basidial development is not
localized at any one point on the gill. The
wedge-shaped section may be an adaptation to
minimize wastage of spores should the fruit body
be tilted from the vertical. Buller (1909) calculated
for the field mushroom Agaricus campestris
that a displacement of 2°30’ from the vertical
would still allow all the spores to escape.
Adjustments in the orientation of the stipe and,
sometimes, of the gills themselves may further
help to minimize wastage. The topic of gravitropism
(gravimorphogenesis), i.e. the re-orientation
by stipe bending or gill curvature in
displaced basidiocarps to restore hymenia to a
vertical position, is discussed on p. 546.
Gills of the inaequi-hymenial (inaequihymeniiferous)
type are characteristic of the
ink-caps (Coprinus sensu lato) where the gills are
not wedge-shaped in section, but parallel-sided,
and often held apart by cystidia (see Fig. 19.7).
The term inaequi-hymenial refers to the fact that
the hymenium develops in an unequal manner,
with basidia ripening in zones. In Coprinus a wave
Fig19.7 Coprinus atramentarius.Vertical section of the parallel-sided gills showing basidia, interspersed by globose paraphyses
and a cystidium extending across the space between adjacent gills to make contact with the surface of the opposing gill.The dashed
arrow indicates the trajectory (sporabola) taken by a projected spore.