Scanning electron microscopy of freeze-fractured sclerotia of Physarum polycephalum

The ultrastructure and architecture of freeze-fractured sclerotia of Physarum polycephalum was studied by a scanning electron microscope (SEM). The sclerotia are built of many spherules grouped together in a common outer coat. Each spherule has hard walls which separate it from its neighbors. The spherules are rounded in 2-day-old sclerotia, and have a lobe-like structure 3 weeks later. A new simple technique for obtaining freeze-fractured biological material is described and compared with freeze-fracture in a freeze-etching apparatus. The ultrastructural details of the fractured sclerotia are described.