SPORE DISCHARGE IN THE ASCOMYCETES

Abstract

T HE object of this paper is to give a comprehensive account of the spore discharge in Pyrenomycetes'. It must be recognised at the outset that discharge is only the preliminary step in spore dispersal. The function of this discharge is to free the spores, which are invariably sticky, from immediate contact with the parent body so that they may subsequently be dispersed. In the majority of cases dispersal is brought about by air currents, but in the coprophilous forms animals are the agents concerned. The ascus, in Pyrenomycetes, is essentially an explosive sporangium except in certain clearly degenerate forms (e.g. Chaetomittm). It is usually elongated and limited by a thin elastic cell wall. Within this, in the mature ascus, is a very thin lining layer of cytoplasm, the semi-permeable membrane of the ascus. This encloses a relatively large volume of ascus sap, which is probably an aqueous solution of sugars derived from the glycogen which is present in the epiplasm of the young ascus. The spores hang together more or less firmly by their own stickiness and are suspended in the solution in the upper region of the ascus by a mucilaginous strand attaching the apical spore to the tip of the ascus. When mature the ascus is in a state of strain, the elastic wall being greatly stretched by the osmotic pressure of the ascus sap. Finally rupture occurs, by the opening of a pore in an apical region of extra thinness (e.g. Leptosphaeria), by the dislodgment of an apical plug (e.g. Hypocopra) or by the separation of a distinct cap (e.g. Podospora). Rupture is followed instantly by the