Introduction to Fungi, Third Edition

TYPESOFFRUITBODY
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the spores may be attached together by mucilaginous
secretions and may be projected for
distances of 30 cm in Ascobolus immersus and
50 cm in Podospora fimicola. The distances to
which individual ascospores are discharged
vary, but are often in the range of 1 2 cm.
In some ascomycetes the ascospores are
not discharged violently, and in such cases the
asci are often globose instead of cylindrical.
The Hemiascomycetes (Chapter 10),
Plectomycetes (Chapter 11) and several other
groups have asci of this type. In Ophiostoma
(Fig. 12.36) and Sphaeronaemella fimicola
(Fig. 12.42) the ascus walls dissolve to release
a mass of sticky spores which ooze out as a drop
held in place by a ring of hairs surrounding the
ostiole at the tip of a cylindrical neck which
surmounts the perithecium. They are dispersed
by insects. Breakdown of asci within the fruit
body is also found in Chaetomium (Fig. 12.9).
Ripe ascospores are extruded from the neck of
the perithecium in a tendril. Possibly they are
dispersed by jerking movements generated as
the rough-walled perithecial hairs twist around
each other. Tendrils of ascospores are sometimes
found in ascomycetes which normally discharge
their spores violently, e.g. Daldinia concentrica
(Plate 5a), Hypocrea pulvinata (Plate 5c) and Nectria.
In many marine ascomycetes the ascus walls
are evanescent and dissolve to release the
ascospores passively. In ascomycetes with subterranean
fruit bodies, e.g. in the truffle Tuber
and its relatives (Figs. 14.7, 14.8), the ascospores
are not discharged violently, but are dispersed
when the fruit bodies are eaten by rodents
and other animals attracted by their characteristic
odour.
8.7 Types of fruit body
The main types of ascomycete fruit body have
been listed earlier (p. 21) and are drawn in
Fig. 8.16). In yeasts and related fungi the asci are
not enclosed by hyphae, but in most ascomycetes
they are surrounded by hyphae to form an
ascocarp (i.e. an ascus fruit body) or ascoma.
An old term for ascus is theca (Gr. theca ¼ a case),
and although this word is not now in general
use, it is still found as a suffix in terms for
different types of ascocarp. Byssochlamys forms
clusters of naked asci (Fig. 11.15). In Gymnoascus
there is a loose open network of peridial hyphae
Fig 8.16 Different types of
ascocarp, diagrammatic and not to
scale. (a) Gymnothecium made up of
branched hyphae which do not
completely enclose the asci.
(b) Cleistothecium completely
enclosing the asci which are formed
throughout the ascocarp.There is no
opening. (c) Apothecium, an open cup
lined by a layer of asci and associated
structures forming the hymenium.
(d) Perithecium with a layer of asci at
the base. It opens by a pore or ostiole.
Its wall or peridium is made up of
flattened cells. (e) Pseudothecium.
The asci are formed within locules in
apseudoparenchymatousascostroma.
There is no peridium. (d) after Ingold
(1971), (e) after Luttrell (1981).