Fungi with a Plasmodial Thallus Division Myxomycota: Slime-Moulds

Abstract

Two distinct phases occur in the life-cycle of a slime-mould. First there is an active assimilative phase in which the thallus, a protozoa-like amoeboid plasmodium, moves with a creeping motion and feeds either saprobically or holozoically by engulfing and digesting bacteria or other solid particles in food vacuoles formed according to need. Second, there is a quiescent phase in which the protoplasm of the plasmodium becomes concentrated into fungus-like sporangia with dry sporangiospores which are meiosporous in their formation. Hyphae are not formed at any time in the life-cycle. Because they appear to have affinities with protozoa and with fungi, the slime-moulds have always been peculiarly difficult to classify. Further difficulties arise because some slime-moulds (Class Myxomycetes) are free-living while others (Class Plasmodiophoromycetes) are endoparasites in cells of higher plants and also differ in several other respects from the free-living types. In addition, two other Orders of slime-organisms, the Acrasiales and the Labyrinthulales, are often considered in this context.