The Myxomycetes or slime moulds occupy a dubious systematic position. As they show marked affinities with the Protozoa, some botanists favour their exclusion from the plant kingdom, while others consider that they occupy a position among the plants equal in status with the true fungi.
They resemble the true fungi in the absence of chlorophyll as well as in the nature of reserve food materials, but they differ from them in having a single, large, naked, multinucleate amoeboid protoplast (Plasmodium or pseudo-plasmodium).
The Myxomycetes are mainly terrestrial organisms, commonly found on fallen leaves, decaying wood, humus soil, etc. They are cosmopolitan in their distribution.
The free-living plasmodia of slime moulds look like gigantic, amoeba and may be several centimetres in diameter. A plasmodium is capable of a creeping motion with the help of pseudopodia, which are finger-like protrusions developed from the body, and are alternately pushed out and withdrawn in succession.
The vegetative body is multinucleate and cytoplasmic movements may be noted within it. Like amoeba it can also ingest solid food, such as spores, small remains of plant or animal bodies, bacteria and other microscopic organisms.
At the time of reproduction an entire plasmodium comes out of the substratum, forms a heap and gives rise to one or a few stalked or sessile sporangia. The sporangia are variously shaped. There is usually found a network of tube-like structures called the capillitium, within a sporangium, and numerous small spores, each surrounded by a wall of its own, are found in the meshes of the capillitium.
On maturity, the sporangial wall ruptures and the spores are dispersed. Each spore, on germination, gives rise to 1-4 uniflagellate-like bodies, which may fuse in pairs immediately or undergo vegetative multiplication. If the swarmers unite in pairs, an amoeboid zygote is produced, which ultimately develops into a multinucleate plasmodium.
Classification:
The Myxomycetes include about 50 genera and 400 species and are generally divided into two subclasses:
(1) Endosporeae, where the spores are produced within the sporangium, and
(2) Exosporeae, where the spores are borne externally on branched pillar-like structures.
The former subclass consists of the following genera which are found in India – Physarum, Physarella, Trichemphara, Craterium, Diderma, Diachea, Didymium, Stemonites, Comatricha, Lamproderma, Cribraria, Lycogala, Trichia, Hemitrichia, Cornuvia, Arcyria, Perichaena, while the latter one is represented in India by the only genus Ceratiomyxa.
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