untitled

Myxomycota – the plasmodial slime

moulds

The plasmodial slime moulds are wall-less organisms

that consist of a multinucleate network of protoplasm

(the plasmodium; Fig. 2.36) exhibiting rapid, rhyth-

mic surges of protoplasmic streaming. These organisms

are commonly seen in the autumn on moist rotting

wood, on senescing fungal fruitbodies and on similar

organic substrata where bacteria are abundant. They

engulf bacteria and other food particles by phago-

cytosis. The plasmodium typically develops within a

substrate but then migrates to the surface in response

to nutrient depletion and the whole plasmodium con-

verts into fruiting structures (sporangia) containing

44 CHAPTER 2

Fig. 2.36Myxomycota. (a) A plas-

modium of Physarum polycephalum

growing on an agar plate. Note how

the plasmodium, which was inocu-

lated in the center of the plate, has

migrated towards the margin, where the

protoplasm has amassed. (b) A decay-

ing bracket fungal fruitbody (about

15 cm diameter) completely covered

by cream-colored sporing structures

of the myxomycete Fuligo septica. (c)

Mature sporangia of the slime mould

Physarum cinereumon a grass blade

about 4 mm diameter; many of the

sporangia have opened to release the

dark gray spores. (d) Immature, pink

sporangia of Lycogalaon the surface of

rotting wood; each sporangium is

about 1 cm diameter. (e) Similar spo-

rangia 5 days later, when the spo-

rangia had matured, turned gray, and

consisted of a thin papery sac that

ruptured to release the spores.

(a) (b)

(d) (e)

(c)

Fig. 2.35The life cycle of Dictyoste-

lium discoideum. (Courtesy of Florian

Siegert ©. From: http://www.zi.biologie.

unimuenchen.de/zoologie/dicty/

dicty.html)

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