Slime Mold, an organism with some characteristics similar to those of fungi, and other characteristics similar to those of protists. There are more than 500 species of slime molds. They creep on decaying wood and in moist soil, ingesting bacteria and decaying vegetation. There are two major groups of slime molds: plasmodial, or true, slime molds and cellular slime molds.
The body of a plasmodial slime mold is the plasmodium, a thin, flat mass of protoplasm as long as 12 inches (30 cm). It does not have any cells, but its protoplasm contains structures similar to cell nuclei. The plasmodium is slimy to the touch and may be yellow, red, purple, or colorless. In response to adverse conditions (such as a lack of moisture), the plasmodium produces sporangia, typically round structures borne on stalks. Through an asexual process, sporangia produce structures called spores. The spores are scattered by the wind. When there is a sufficient amount of moisture, the spores develop into reproductive cells called gametes. Through a sexual process, the fusion of two gametes produces a new plasmodium.
Several species of microscopic, parasitic slime molds known as plasmodiophorans are classified with plasmodial slime molds by some biologists. Plasmodiophorans cause club-root disease in cabbage roots and powdery scab in potato plants.
The body of a cellular slime mold consists of many cells. They form a sluglike mass called a pseudoplasmodium. The pseudo-plasmodium eventually transforms itself into a stalklike structure called a sorocarp, which releases spores. Amoeboid cells emerge from the spores. After feeding for some time, the amoeboid cells gather together to form a new pseudoplasmodium. A cellular slime mold does not usually have a sexual stage in its life cycle.
Most biologists place slime molds in the kingdom Protista. Some biologists, however, place slime molds in the kingdom Fungi. Plasmodial slime molds are usually placed in the phylum Myxomycota; cellular slime molds in the phylum Acrasiomycota. Plasmodiophorans are placed in the phylum Myxomycota or the phylum Plasmodiophoromycota. The species of plasmodiophoran that causes club-root disease is Plasmodiophora brassicae; the species that causes powdery scab, Spongospora subterranea.