Introduction to Fungi, Third Edition

EXAMPLES OF MUCORALES
185
Fig 7.17 Absidia glauca. (a) Habit showing whorls of
pear-shaped sporangia. (b) Intact and dehisced sporangia.
Note the single pointed projection on certain columellae.
(c) Zygospore showing the arching suspensor appendages.
upon contact with an object. The sporangia are
black and melanized, presumably as a protection
against UV irradiation. Grove (1934) has written
a monograph of the family which has stood
the test of time.
Pilobolus
The generic name means literally the ‘hat
thrower’, referring to the sporangial discharge
mechanism. If fresh herbivore (e.g. rabbit,
sheep, deer, horse) dung is incubated in light,
the characteristic bulbous sporangiophores of
Pilobolus appear after a preliminary phase of
fruiting of Mucor which may last for 4 7 days
(Fig. 7.20, Plate 3f). Nine Pilobolus spp. previously
recognized have been reduced to five, but
including a number of varieties (Hu et al., 1989).
Common species are P. crystallinus, P. kleinii (¼
P. crystallinus var. kleinii), and P. umbonatus (¼
P. roridus var. umbonatus). Here we adopt the
nomenclature proposed by Grove (1934). As far as
is known all members of the Pilobolaceae are
heterothallic.
A full account of the development and
discharge of the sporangium has been given by
Buller (1934) and Ingold (1971). Discharged
sporangia of Pilobolus become attached to vegetation
surrounding the dung on which they were
produced. When the vegetation is eaten by a
herbivore, the spores are released into the gut.
In the voided faeces, the spores germinate to
form a mycelium. After about 4 days, the
mycelium near the surface of the dung pellet
forms trophocysts, swollen hyphal segments
coloured yellow by carotenoids (Fig. 7.20).
Sporangiophores develop from the trophocysts
in a regular daily sequence, and the stage of
development can be correlated with the time of
day. During the late afternoon the sporangiophore
grows away from the trophocyst towards
the light and during the night its tip enlarges to
become the sporangium. The swelling of the
subsporangial vesicle takes place mainly between
midnight and the early morning. Young sporangiophores
are highly phototropic even before
their sporangia are differentiated, and the
clear tip of the developing sporangiophore is