Introduction to Fungi, Third Edition

416 HYMENOASCOMYCETES: PEZIZALES (OPERCULATE DISCOMYCETES)
Fig14.1 Pyronema domesticum.
(a) Apothecium showing hymenium
and excipular hairs. (b) Group of
ascogonia and antheridia. (c) V.S.
through developing apothecium
showing several ascogonia
producing ascogenous hyphae, and
the development of paraphyses and
excipulum from the ascogonial
stalks. (d) Enlarged view of the
ascogonium and developing
ascogenous hyphae. (e j) Stages
in the development of asci.
(e) Binucleate tip of ascogenous
hypha beginning to form a crozier.
(f) Quadrinucleate stage.
(g) Septation of crozier to form
a binucleate penultimate cell.
(h) Development of ascus from
binucleate cell. (i) Completion of
first meiotic division.
(j) Completion of second meiotic
division. Note the proliferation of
a new ascogenous hypha from the
stalk cell.
some reports purporting to be on P. confluens
may well have been based on P. domesticum.
These earlier studies include classical accounts
of the cytology of the development of ascogenous
hyphae, croziers and asci (see Moore, 1963).
14.2.1 Development of asci in Pyronema
Both species of Pyronema are homothallic and
grow rapidly in agar culture or on sterilized soil
and within 4 5 days form pink apothecia about
1 2 mm in diameter (Plate 6a; Webster & Weber,
2001). Apothecia of P. domesticum arise from
clusters of ascogonia and antheridia formed
by repeated dichotomy of a single hypha. The
ascogonia are fatter than the antheridia and
each ascogonium is surmounted by a tubular
recurved trichogyne which grows to make contact
with the tip of an antheridium (Fig. 14.1b).
Both antheridia and ascogonia are multinucleate
and, following fusion of the trichogyne with the
antheridium by breakdown of the walls separating
them (plasmogamy), antheridial nuclei
stream into the ascogonium and each antheridial
nucleus becomes paired with an ascogonial
nucleus. Nuclear fusion (karyogamy) does not
occur at this stage, but the paired nuclei remain
associated with each other. Branched investing
hyphae develop from the ascogonial stalks and
envelop the cluster of fertilized ascogonia, ultimately
making up the tissues of the apothecium,
i.e. the medullary and ectal excipulum. Several
ascogenous hyphae extend from each ascogonium
and grow between the surrounding
investing hyphae (Figs. 14.1c,d).
Further development follows the common
ascomycete pattern outlined in Fig. 8.10 (I. M.
Wilson, 1952; Hung & Wells, 1971). The ascogenous
hyphae are branched and septate at their
tips, which recurve to form croziers. The tip of
the crozier is binucleate and the two nuclei