Introduction to Fungi, Third Edition

STRUCTURE AND MORPHOGENESIS OF BASIDIOCARPS
519
combinations according to the mitic system of
description (Gr. mitos ¼ a thread of the warp).
Monomitic basidiocarps are made up of
generative hyphae only. Most agaric fruit bodies
are of this type, containing inflated generative
hyphae with or without clamps. However,
various modified cell types may also be present,
e.g. the lactifers (laticifers) containing latex in
Lactarius (Fig. 19.4). In Lactarius and Russula
(russuloid clade), the flesh contains rosettes
of globose, thin-walled sphaerocysts or sphaerocytes
(see Figs. 19.4 and 19.9c) which give it a
brittle texture. Basidiocarps of the polypore
Bjerkandera adusta are also monomitic, but
here the walls of the generative hyphae thicken
with age. Sarcomitic construction is seen in
the polypore-type basidiocarps of Meripilus, made
up of inflated sarco-hyphae which function as
skeletal elements.
Dimitic fruit bodies, produced by various
members of the polyporoid and russuloid clades,
may show several kinds of construction. Dimitic
fruit bodies with binding hyphae (i.e. generative
and binding hyphae) are found in
the basidiocarp of Laetiporus sulphureus (see
Plate 10b). The dissepiments (i.e. the blocks of
flesh separating the tubes) are, however, monomitic.
Dimitic fruit bodies with skeletal
hyphae are found in Heterobasidion annosum
(see Fig. 19.26b), whereas dimitic basidiocarps
with skeleto-ligative hyphae are found in Lentinus
and Ganoderma.
Trimitic fruit bodies contain all three kinds
of hypha shown in Fig. 19.3. A good example
is Trametes versicolor, a common bracket fungus
on hardwood stumps, trunks and branches
(see Plate 10a). At the growing margin of
the fruit body and in the dissepiments, construction
is dimitic, composed of generative and
skeletal hyphae. Binding hyphae develop in the
adult flesh behind the growing margin. The term
sarcotrimitic has been used to describe fruit
body construction in Trogia where there are
generative, binding and sarco-hyphae.
19.2.2 Development of basidiocarps
Basidiocarps begin their development from a
hyphal knot, an aggregation of hyphae formed
usually on the secondary (i.e. dikaryotic) mycelium.
The surface of the hyphae forming the
fruit body primordium is often non-wettable
due to hydrophobin rodlets (Wessels, 1994, 2000).
This property ensures that air-filled channels
are present within basidiocarps, allowing efficient
gas exchange to occur even under wet
conditions (Lugones et al., 1999). The first-formed
hyphae making up the young fruit body are
little differentiated from normal vegetative
hyphae and are termed protenchyma but, as
differentiation proceeds, the hyphae of the
Fig19.4 Lactariusrufus. Cells from the pileus,
including thin-walled septate generative hyphae,
a wider, thicker-walled laticiferous hypha which
contains a milky latex, and clusters of globose
sphaerocysts.