Introduction to Fungi, Third Edition

50 PROTOZOA: MYXOMYCOTA (SLIME MOULDS)
Fig 2.10 Spore germination and swarmers in Physarum and Reticularia.a.Physarum polycephalum:1,sporesgerminating torelease
myxamoebae; 2, uniflagellate and biflagellate swarmers, note the pseudopodia at the front end of one swarmer; 3, myxamoeba;
4, fusion between two myxamoebae. b. Reticularia lycoperdon:1, spore showing cracked wall; 2, swarmers, one with pseudopodia;
3, encystment stage; 4, fusion between two swarmers.
form (disc-like, membranous, horny or spongy).
In P. polycephalum, sexual reproduction is triggered
by environmental factors such as
starvation and light, and by chemical factors,
e.g. Ca 2þ and malate (Renzel et al., 2000).
Depending on species, the sporophores may
take a range of shapes. Intermediates between
these different types of sporophore are possible.
The most common form is the sporangium,
a vessel enclosed by a wall (peridium) within
which the spores are contained (Plates 1e,f,h).
Protoplasmodia produce only one sporangium
each, but numerous sporangia may arise from
phaneroplasmodia. Sporangia may be stalked
or sessile. A second common sporophore is the
aethalium (Gr. aethes ¼ irregular, curious,
unusual) in which the entire plasmodium
becomes converted into a hemispherical or
cushion-shaped structure (Plates 1b d,g). This
can comprise several sporangia, but these have
usually lost their structural identity and are
surrounded by one common peridium. In a
pseudoaethalium, several sporangia are grouped
together but are still recognized as structurally
distinct. In the plasmodiocarp, the protoplasm
accumulates in the main veins of the plasmodium,
and spores are produced there.
Frederick (1990) has described methods for
the isolation and cultivation of myxomycetes.
Some species, such as Physarum polycephalum,
can be grown in axenic culture and have
become valuable systems for experimentation.
Other species need to be fed with bacteria or
sterile oat flakes. Plasmodia can be maintained
for prolonged periods in a vegetative state, and
sclerotia can be stored dry for months. Spores