A Myxomycete with a Singular Myxamoebal Encystment Stage

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Abstract
An aberrant culture of what is probably Didymium nigripes is described in which free-living myxamoebae seemingly constitute the primary trophic phase. Following vegetative growth, most of the myxamoebae collect into simple aggregations and form mounds or erect tapered columns prior to encystment. Such columns consist of similar microcysts throughout and show no demarcation into areas of supportive vs. propagative cells. Microcysts germinate and release myxamoebae which may promptly renew vegetative growth, or in aqueous media develop flagella and form swarm cells. Plasmodia appear rarely in the myxamoebal cultures, but when formed these can be cultivated by frequent transfer to fresh substrates pre- inoculated with Escherichia coli or Aerobacter aerogenes. When not retransferred, such plasmodia either produce poorly formed sporangia within 6–8 da or, failing to fruit (as often occurs), collect into darkly pigmented moribund masses and disintegrate. Sclerotia are not formed naturally and attempts to induce sclerotization have been unsuccessful. Of special significance is the consistent reappearance after an additional week (±) of the myxamoebal stage at the sites where fructification was effected or attempted. The origin of the emergent myxamoebae is not known, but their presence, renewed growth, and subsequent encystment serve to insure continuity of the slime mold even in the absence of normal sporangia and spores.

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