Introduction to Fungi, Third Edition

STRUCTURE AND MORPHOGENESIS OF BASIDIOCARPS
523
Fig19.8 Modes of gill attachment to the stipe, and
their terminology.
of gill maturation begins at the cap margin and
passes slowly upwards and inwards. After the
basidia at the lower edge of the gill have discharged
their spores, the gill tissue undergoes
autolysis (deliquescence) into an inky black
liquid which drips away from the cap. The gravitropic
gill curvature characteristic of aequihymenial
types is absent, but the stipe may still
curve to bring the gills into an approximately
vertical position.
An important criterion for identification of
gill-bearing agarics in the field is the way in
which the lamellae are attached to the stipe
(Fig. 19.8). Gills are said to be free if their blade
does not touch the stipe. Adnate gills show
attachment to the stipe with their entire base,
whereas adnexed gills are attached only partially
to the stipe. In sinuate gills, the gill margin
shows an S-shaped curve near the point of
junction with the stipe. Decurrent gills run
down the surface of the stipe.
19.2.4 The hymenophoral trama
The hymenophore structures of some
Homobasidiomycetes are shown in Fig. 19.9. In
most hymenophores, there is a central group of
hyphae running from the underside of the cap to
the tip of the gill, pore or spine, and these
hyphae are collectively called the hymenophoral
trama. Various distinctive types have been
recognized by Reijnders and Stalpers (1992), but
these do not correlate well with the phylogeny of
the Homobasidiomycetes as shown in Fig. 19.2.
1. In the trametoid type (e.g. in Lentinus,
Fistulina and Schizophyllum), development begins
with a bundle of parallel hyphae from which
branches grow out in various directions and may
become interwoven.
2. In the cantharelloid type, the developing
hymenophore is at first smooth and covered by a
palisade of hyphae which will form
the hymenium. Later, locally increased
activity in the subhymenium may result
in irregular ridges (Serpula), more regular veins
(Cantharellus, Craterellus) or gills (Hygrophoropsis).
3. The boletoid type is shown by Boletus and
relatives (Fig. 19.9a). The first stage is made up of
divergent hyphae which form a narrow central
layer (mediostratum), followed by swelling and
differentiation of the cells to form a lateral
stratum. The diverging hyphae of the lateral
strata curve sharply outwards to form the
hymenium, and the term divergent trama is
therefore used to describe this type of hymenophore.
A subhymenium made up of narrow
interwoven hyphae is also present.
4. The agaricoid type is by far the most
common and includes the coprinoid, russuloid,
agaricoid, pluteoid and amanitoid subtypes. In
cross-section, gills usually appear differentiated
into a central trama, a subhymenium and the
hymenium (Fig. 19.9b). The hyphae in the trama
often run parallel to each other, but in the
pluteoid subtype (e.g. Volvariella and Pluteus), the
wide hyphae making up the trama are arranged
in a V-shaped pattern (Fig. 19.9d), and this is
called the inverted trama. In the russuloid
subtype (Russula and Lactarius), the mature
trama is said to be intermixed because in
addition to the narrow generative hyphae it
contains swollen cells (sphaerocysts) of very
different width (Fig. 19.9c). The amanitoid type
shows a central mediostratum made up of
narrow generative hyphae from which wider
subhymenial elements diverge (Fig. 19.9e). This
type of trama is described as bilateral.