Myxomycetes

MYXOMYCETES (Myxomycetes, syn. Myxothallophyta), a group (phylum or class) of lower organisms occupying an intermediate position between plants and animals, and therefore also called Mycetozoa (fungi-animals). Myxomycetes are especially characterized by the structure of their vegetative body, represented by the so-called plasmodium—a naked mass of protoplasm, mostly in the form of a network, possessing active movement and sometimes reaching considerable sizes (up to 0.5 m and more in diameter). The study of these considerable masses of protoplasm (more precisely, protoplasm together with nuclei), living freely, is of significant scientific interest and has attracted a number of first-class scientists (de Bary, Pfeffer, Reinke, and others). Their work has largely clarified the composition of this protoplasm and its reactions to environmental influences. In the vegetative state, the plasmodium possesses a clearly expressed positive hydrotaxis and negative phototaxis, which is why in natural conditions it crawls into the interior of the substrate (usually a pile of plant remains—leaves, etc.), into its more humid and dark regions; there it feeds and grows, and then its tactic reactions change, and it crawls out onto the surface, where it forms reproductive organs called fruit bodies or sporangia; they have the appearance of sacs of various shapes and sizes, sometimes brightly colored; inside them, spores develop in large quantities, usually mixed with thin sterile filaments, the so-called capillitium, which after the rupture of the sporangial wall plays a known role in loosening and dispersing the spore mass due to the hygroscopic movements inherent to it. Germinating in water, the spores give mobile stages in the form of uniflagellate zoospores, which soon turn into amoebae. From the fusion of the latter, a plasmodium is formed anew. Interestingly, the nuclei also soon fuse pairwise in the process, so that in the formation of the plasmodium one can see certain features of the sexual process. As organisms lacking chlorophyll, Myxomycetes can feed only on ready-made organic substances. This is achieved partly by engulfing small food particles and digesting them inside the plasmodium, and mainly by absorbing nutrients in a dissolved form from the external environment, upon which the plasmodium acts by enzymes secreted to the outside. Over 300 species of Myxomycetes are known. Many of them are very common in our country in plant remains: stumps, fallen leaves, tree bark, tanning bark, etc., where their fruit bodies form most extensively in autumn. Myxomycetes have no practical significance with the exception of a few parasitic forms, such as Plasmodiophora Brassicae, which causes a disease of the roots of cabbage and other crucifers known as clubroot.