Phylum Myxomycota The Plasmodial Slime Molds

In the Ripley's "Believe It or Not" pavilion at the Chicago World's Fair in 1933, there was an exhibit of "hair growing on wood." The "hairs," while indeed superficially resembling short human hair, were actually the reproductive structures of a species of slime mold (Fig. 18.29). These curious organisms are totally without chlorophyll and are incapable of producing their own food. They are a bit of a puzzle to biologists because they are distinctly animal-like during much of their life cycle but also distinctly fungus-like when they reproduce.

The tiny, roundish spores of the more than 500 species of slime mold average only 10 to 12 micrometers in diameter and are individually invisible to the naked eye. Nevertheless, they are present nearly everywhere and are especially abundant in airborne dusts.

If you place almost any dead leaf or piece of bark in a dish and add a food source, such as a few dry oatmeal flakes to which a drop or two of water has been added, the odds are that slime mold spores will be present and will germinate. If the dish is covered, the spores will sometimes germinate in as little as 15 minutes, but germination usually takes several hours or longer. Within a few days, a glistening mass of active slime mold protoplasmic material, looking something like the netted veins of a leaf, may appear. This material, whose "veins" tend to merge into the shape of a fan at its leading edges, is a slime mold plasmodium (Fig. 18.30).

If the plasmodium is examined with a microscope, it becomes apparent that there are no cell walls present. The protoplasm in the veins, particularly toward the center, flows very rapidly and rhythmically. The protoplasmic movement may stop momentarily at regular intervals and then resume its flow, sometimes in the opposite direction.

Plasmodia are often white, but they also may be brilliantly colored in shades of yellow, orange, pink, blue, violet, or black. A few are colorless and more or less transparent. Plasmodia are found on damp forest debris, under logs, on old shelf or bracket fungi, sometimes on older mushrooms, and in other moist places where there is

Stemonitis Reproductive Stage
Figure 18.29 Reproductive bodies (sporangia) of the plasmodial slime mold Stemonitis, x20.

The algae are the chief source of photosynthesis across the open ocean and the main basis for the food webs of the open ocean ecosystem, the most extensive on the planet. Photosynthetic algae are major contributors to the oxygen of our atmosphere and may make a similar contribution to the atmospheres of long-distance spacecraft. The Protista also include the heterotrophic slime molds, protozoans, and oomycetes, as well as the euglenoids, which are both photosynthetic and heterotrophic. Seaweeds are an important source of useful chemicals, ranging from antibiotics and insecticides to anti-cancer agents. In contrast to the human benefits derived from seaweeds, the water molds, another group of protists, cause diseases in many crop plants, such as the late blight of potatoes that created the Irish Potato Famine of 1846 in which over one million people starved to death and millions more were forced to emigrate.

Physarum Life Cycle

Figure 18.30 A plasmodium of the slime mold

Physarum, x10.

Figure 18.30 A plasmodium of the slime mold

Physarum, x10.

dead organic matter. Plasmodia tend to flow forward at a rate of up to 2.5 centimeters (1 inch) or more per hour, often against slow moisture seepage, feeding on bacteria and other organic particles as they go. They contain many diploid nuclei, all of which divide often and simultaneously as growth occurs. With an adequate food supply, a plasmodium may increase to 25 times its original size in just 1 week.

Dramatic events take place when significant changes in food supplies, available moisture, light, and other environmental features occur. The plasmodium usually is converted, often quite rapidly, into many separate small

Phylum Myxomycota

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  • veera
    What is phylum myxomycota?
    8 years ago
  • kadyn
    How to build a myxomycota?
    8 years ago
  • Kenneth
    Is plasmodial slime mold photosynthetic or heterotrophic?
    8 years ago

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