A FUNGAL FRUIT BODY COMMON IN POSTGLACIAL PEAT DEPOSITS

Abstract

In the course of routine pollen identification during the past Z years, samples prepared from peat deposits of various ages have yielded examples of a fungus fruit body of very characteristic appearance. These resemble in structure the ascomata (thyriothecia) of Microthyrium, a type of organization which is, however, encountered rather widely, in the Sphaeropsidales and the Microthyriaceae. Mature specimens take the form of circular disks or shallow convex shields with a regular radiate structure of adherent hyphae. The largest disks reach IOO-I35 it in diameter, but many smaller examples occur. It is possible to speculate that the fruit bodies may be either different stages of maturation of one species, or that two different species may be present, one with a pronounced central neck and the other without. In both types frequent and regular transverse divisions of the hyphae yields a single-layered tissue of approximately square cells about 3-5 u wide, and the thinness and paler colour of the transverse walls suggest that the disk has a marginal growth region. The central area shows a less pronouncedly radial structure, and in miniature disks this gives an intact small central plate, but in large specimens the centre of the disk is occupied by a projecting collar or neck of cells surrounding a regular circular opening approximately 9 or io u in diameter. The whole fruit body has the dark purplish brown colour so often seen in fungal material occurring in peats and organic muds, and this is especially pronounced where the walls are thick: it is especially so in the small and thick-walled cells of the neck. As will be observed from the photographs (P1. i), the neck in some specimens projects considerably above the general level of the disk, and indeed the latter often takes the form of a shallow funnel or bell. It would be unwise to assume that these shapes are necessarily those of the living fungus, for we now observe them detached from the substrate on which they grew, and only after severe chemical treatment. In many of the larger specimens the neck bears a number of conspicuous spinous processes of rather variable length and form (P1. i, ? m). The actual margin of the neck is nevertheless regular around the central opening and without a fimbriate hyphal rim. In the great majority of examples the disk is apparently one-layered throughout, but in a few instances there may possibly be present a second and lower layer, presumably the basal plate.