Delimitation of the Gametangia of Rhizopus sexualis (Smith) Callen: an Electron Microscope Study of Septum Formation

Abstract

The development of the septa which cut off the gametangia of Rhizopus sexualis from the suspensor cells was studied by electron microscopy. The edge of the ingrowing septum extends by the incorporation of coalesced vesicles which were previously aligned in the plane of the developing septum. The membranes surrounding these vesicles fuse to form the plasmalemmas of the gametangium and suspensor cell and are eventually continuous with the plasmalemma of the original progametangium. New wall material is laid down between these plasmalemmas. Associated with this process is a considerable increase in complexity of the endoplasmic reticulum which forms broad, irregular bands on either side of the septum. Fine tubules, resembling plasmodesmata, pass through the wall at intervals. Thickening of the septum proceeds more rapidly on the gametangial side.