The Morphology of Leptodiscus terrestris, and the Function of Setae in Spore Dispersal

Abstract

SUMMARYLeptodiscus terrestris requires light for the formation of both fruiting structures and conidia. The fruiting structure is meristogenous in origin. Branches are produced from an initial, multinucleate, hourglass-shaped cell. Sporogenous cells develop at the apex of each branch, and these in turn produce more sporogenous cells, eventually forming a thin, saucer-shaped fruiting structure.The spores first appear as small protuberances on the inner edge of the sporogenous cells. These protuberances enlarge and elongate and as they develop, they appear to be attached to the sporogenous cells by a very short stalk. This stalk disappears when the spores mature. When the spores reach their mature size, the setae are formed. The seta on the upper end of the spore develops at the point of greatest curvature toward the concave side, and the seta on the lower end develops at the edge of the slightly flattened surface near the concav side of the spore. One crop of spores is produced by the sporogenous cells each day. Spores are held together in a head by a mucilagenous substance.When the spores are in the head, the setae are folded back against the spore wall on the concave side. When the mucus is dissolved, the setae unfold and expell the spores outward with considerable force. The same mechanism of spore dispersal also appears to occur in Menispora tortuosa, a fungus with setulate conidia similar to those of L. terrestris.