Introduction to Fungi, Third Edition

48 PROTOZOA: MYXOMYCOTA (SLIME MOULDS)
by a slime sheath. Plasmodia vary in size and can
be loosely grouped into three categories.
(1) Protoplasmodia are inconspicuous microscopic
structures usually giving rise only to a
single sporangium. They resemble the simple
plasmodia of protostelids.
(2) Aphanoplasmodia (Gr. aphanes ¼ invisible)
are thin open networks of plasmodial strands.
The aphanoplasmodium is transparent, with
individual strands only 5 10 mm wide and the
entire plasmodium about 100 200 mm in diameter.
Most aphanoplasmodia are only seen
with the aid of a dissection microscope.
(3) Phaneroplasmodia (Gr. phaneros ¼ visible)
are large sheets or networks with conspicuous
veins (Fig. 2.8a) within which the protoplasm
shows rhythmic and reversible streaming, each
pulse lasting about 60 90 s. This striking phenomenon
is readily observed with a dissection
microscope and is probably due to interactions
of Ca 2þ ions with cytoskeletal elements lining
the veins (see Section 2.5.3).
2.5.1 Life cycle of myxomycetes
The life cycle of Physarum polycephalum, a typical
myxomycete, is summarized in Fig. 2.9. The plasmodium
is diploid and feeds by phagocytosis of
bacteria, yeasts or fungal mycelia or spores.
It gives rise to a sporophore under appropriate
conditions. The haploid spores are dispersed
Fig 2.8 Phaneroplasmodia of Physarum polycephalum.
(a) Margin of extending plasmodium.The protoplasm
is particularly dense at the advancing edge.Further
behind, protoplasm is concentrated in large veins
which show rhythmic pulsation. (b) Fusion between
compatible plasmodia. Note the complete fusion of
veins. (c) Lethal reaction following fusion between
incompatible plasmodia. (a) from Carlile (1971),
(b) and (c) from Carlile and Dee (1967), by permission
of Academic Press (a) and Macmillan Journals (b,c).
Original prints kindly supplied by M. J.Carlile.