Introduction to Fungi, Third Edition

422 HYMENOASCOMYCETES: PEZIZALES (OPERCULATE DISCOMYCETES)
Fig14.6 Ascobolus furfuraceus. (a) Group of asci and
paraphyses.One ascus is mature and contains
purple-pigmented ascospores. (b) The same ascus as
shown in a after discharge.The ascus has decreased in size
during discharge. Note the operculum. (c) Arthrospores
(oidia) developed in five-day-old culture. (d) Coiled
ascogonium formed in a single ascospore culture within
48 h of adding oidia of the opposite mating type.
The trichogyne of the ascogonium has grown towards
the oidium and has fused with it.
14.5.2 Apothecium development
The development of apothecia of A. furfuraceus
has been studied by various authors, including
Wells (1970, 1972) and O’Donnell et al. (1974).
The fertilized ascogonium becomes surrounded
by sheath hyphae which develop from the
ascogonial stalk, and the paraphyses and excipular
tissues develop from the sheath hyphae.
The ascogonium gives rise to numerous ascogenous
hyphae. Van Brummelen (1967) has
distinguished two kinds of ascocarp development
in Ascobolus. In gymnohymenial forms,
the hymenium is exposed from the beginning
until the maturation of the asci. In cleistohymenial
forms the hymenium is enclosed during
its early development. Ascobolus furfuraceus and
A. immersus are examples of cleistohymenial
development.
14.5.3 Ascosporogenesis
The details of ascosporogenesis have been
studied in A. immersus by Wu and Kimbrough
(1992) and in A. stictoideus by Wu and Kimbrough
(2001). Although A. immersus has smooth ascospores
and A. stictoideus has ornamented spores,
development is very similar. As in most ascomycetes,
invagination of the ascus vesicle encloses
the young ascospores by a two-layered sporedelimiting
membrane. The inner layer forms the
plasmalemma of the ascospore, whilst the outer
membrane forms a perisporic sac. The primary
spore wall is laid down between these two
membranes. It consists of an electron-transparent
endospore and a laminated epispore. The
perisporic sac is variable in thickness and
projects into the epiplasm of the ascus.
At points of contact with the perisporic sac