Disappearance of the surface sheath from Dictyostelium discoideum Sorus during late culmination

After the aggregation stage of Dictyostelium discoideum, the cell mass is surrounded with the thin surface sheath. There is a difference in opinion in the work by previous authors. According to Gezelius and Ranby (1957) the whole sorus loses the sheath. Raper and Fennell (1952), and Murata and Ohnishi (1980) indicated that only the papilla, or both the papilla and the lower part of the sorus are enveloped, respectively. On the other hand, Watts and Treffry (1976) claim that the whole fruiting body is enclosed in a sheath. In this study, the surface of the pseudoplasmodium, the culminating cell masses and mature fruiting body was examined by means of both SEM and TEM. It was found that the surface sheath is lost as the sorus is rounding out and spores are maturing. At the end of development the sheath remains only on the papilla and not on the basal end of the mature sorus. The possibility of disappearance of the sheath through digestion and engulfment is discussed.