[The regeneration of the plasmalemma of Physarum polycephalum]

After experimental rupture, the plasmalemma of protoplasmic droplets and isolated protoplasm ofPhysarum polycephalum regenerates by means of membrane vesiculation. Various (mucus- and food-) vacuoles are responsible for the new formation of the plasmalemma. Immediately after removal of the old plasma membrane, many vacuoles accumulate below the boundary between the protoplasm and the surrounding medium in a region of 5-10 Μ depth. Later some large vacuoles, which are strongly flattened parallel to the surface of the protoplasm, originate by means of successive confluence of these single vesicles. The large vacuoles finally fuse to a single vacuole which surrounds the whole protoplast. Thedistal membrane of this vacuole disintegrates together with degenerating protoplasmic components. Theproximal membrane of the vacuole represents the new surface of the surviving protoplasm. The process of regeneration of the plasmalemma takes 5-6 sec and seems not to depend on the kind of medium surrounding the protoplasm. Inspite of the fact that during a part of the first phase of regeneration, the cytoplasm is "naked" (i.e. without a membranous boundary), there is no migration of particulate substances from the outer medium into the surviving protoplasm, as shown by experiments with the marker substanceaerosil.