Introduction to Fungi, Third Edition

600 HETEROBASIDIOMYCETES
21.3.1 Dacrymyces
Orange gelatinous cushions about 1 5mm in
diameter, so common on damp rotting wood,
are the fructifications of D. stillatus (Fig. 21.3a).
Close inspection with a hand lens reveals that
the fruit bodies are of two kinds: soft, bright
orange, hemispherical cushions and firmer, pale
yellow, flatter structures. The bright orange
cushions are conidial pustules which consist of
hyphae whose tips are branched and fragment
into numerous dikaryotic arthroconidia (Fig.
21.4c). The cells are packed with oil globules
containing carotenoids. Such conidia are readily
dispersed by rainsplash and are obviously similar
in function to the splash-dispersed conidia of
Nectria cinnabarina (see Plate 5d). The yellow
flatter structures are basidial cushions which
are attached centrally to the woody substratum.
The surface layer is composed of clusters of
forked basidia (Fig. 21.4b) which arise from
dikaryotic hyphae. Each basidium forms two
haploid basidiospores. After discharge, a basidiospore
undergoes nuclear division and
septation to give four cells. Depending on environmental
conditions, each cell germinates by
means of a monokaryotic haploid germ tube
or by a short conidiophore (denticle). Conidia
may also arise on older hyphae. They germinate
to give monokaryotic hyphae. Dikaryotization
occurs when two compatible monokaryotic
hyphae fuse. Mossebo and Amougou (2001) have
shown that the parenthesome and dolipore
complex dissolve in order to facilitate passage
of nuclei through the septum in the course of
dikaryotization. Dacrymyces stillatus is heterothallic
with a bifactorial (tetrapolar) mating system.
Cells of the secondary mycelium are usually but
not unfailingly dikaryotic (Mossebo, 1998).
21.3.2 Calocera
At first sight the ubiquitous cylindrical orange
outgrowths of C. viscosa from coniferous logs
(Plate 11g), or the smaller C. cornea from hardwood
logs (Fig. 21.3b), could be mistaken for
species of Clavaria. However, the gelatinous
texture and the characteristically forked basidia
(Fig. 21.5) place them in the Dacrymycetales, and
this placement has been confirmed by molecular
phylogenetic studies (Weiss & Oberwinkler, 2001).
Ingold (1983b) has carefully observed the fate
Fig 21.5 Calocera viscosa. (a) T.S. through hymenium with furcate basidia at different stages of development. (b) Freshly discharged
basidiospores which are aseptate.The clear area in each spore shows the displacement of cytoplasmic contents by the single
nucleus. (c) Two 24-hour-old basidiospores on tap-water agar. Each spore has produced two conidiophores bearing microconidia
on denticles. (d) Direct germination of a basidiospore has given rise to monokaryotic hyphae which are forming microconidia.
The septum dividing the spore into two is clearly visible. (b d) to same scale.