Gross Morphology of the Plasmodium and Its Possible Significance in the Relationships among the Myxomycetes

Abstract

Three general types of myxomycete plasmodia, designated as protoplasmodium, aphanoplasmodium and phaneroplas-modium, are described and illustrated. Protoplasmodia remain microscipic; develop no differentiated fan-shaped regions, veins, or reticulations; and exhibit a slow, irregular streaming. Aphanoplas-modia are flat, transparent, and much less granular than the other 2 types; consist mostly of hypha-like strands which are not well differentiated into outer and inner regions; and form no sheet-like advancing fans until a relatively late stage of development. Phanero-plasmodia are easily visible because of their dense, granular protoplasm; consist of thick veins which are differentiated into a rapidly streaming endoplasm and a jellified ectoplasm; and form conspicuous advancing fans at an early stage of development. Protoplasmodia seem to be characteristic of spp. which form minute sporangia regardless of taxonomic position. Aphanoplasmodia have so far been reported only from spp. which are classified in the Stemonitaceae. Phaneroplasmodia appear to be characteristic of the Physarales. The possibility that the morphology of the plasmodium may be of some significance in determining relationships among major groups of Myxomycetes is discussed.