Introduction to Fungi, Third Edition

244 ASCOMYCOTA (ASCOMYCETES)
Fig 8.15 Ascospore liberation in Cochliobolus cymbopogonis. (a) Ascospore with a recurved tip. (b) Ascus containing a sheaf of
eight spirally coiled ascospores.The ascus is bitunicate but the endoascus is not shown. (c) Ascus during the first stage of discharge.
The ectoascus has broken (arrow), the endoascus has broken at its base and has extended, remaining as a thimble-like cap over
the sheaf of ascospores. (d) An ascus after the release of the ascospores which have straightened out and pushed the broken
endoascus aside. (e) Diagrammatic representation of a section through a pseudothecium showing stages in ascospore release.
Scale bar, (a,b) ¼ 50 mm; (c,d) ¼ 200 mm. After El-Shafie and Webster (1980).
constricted on passing through the ascus pore.
This has been neatly demonstrated by spinning
a transparent disc over the surface of a culture
of Sordaria discharging spores (Ingold &
Hadland, 1959). The ascus contents are laid out
on the disc in the order in which they are
released. Various patterns of spore clumping and
separation are visible, and although in many asci
the eight spores are well separated from each
other, in others there is a tendency for spores to
stick together. Calculations made from
measurements of the length of the ascospore
deposit and the speed of rotation of the disc, as
well as by other methods, have revealed ascospores
to be the fastest-accelerating biological
objects (Trail et al., 2005; Vogel, 2005). The actual
time taken for ascus discharge was estimated by
the rotating disc method to be 0.000024 s (Ingold
& Hadland, 1959). When ascospores stick
together, they are discharged further than
single-spored projectiles. In many coprophilous
ascomycetes (e.g. Ascobolus, Saccobolus, Podospora)