Studies Of Paleozoic Fungi. Iv. Wood‐Decaying Fungi In Callixylon Newberryi From The Upper Devonian

An extensive fungal infection is present in silicified specimens of Callixylon newberryi (Dawson) Elkins and Wieland from the Upper Devonian of Indiana. Fungi are represented by branched, septate filaments with both terminal and intercalary chlamydospores. Clamp connections were not observed. Tracheids of the secondary xylem, decayed in varying degrees, show erosion troughs, cavities, and extensive lysis of tracheid walls. The pattern of decay is most similar to modern-day white rots, which are typically caused by basidiomycetes, while hyphal features are characteristic of either ascomycetes or basidiomycetes. The presence of wood decay coupled with a septate mycelium suggests the presence of higher fungi in the Devonian and indicates a more diverse Devonian mycoflora than has previously been recognized. THE DEVONIAN MYCOFLORA is poorly known. Although a few fungi have been reported from marine environments (e.g., Fry and McLaren, 1 9 5 9; Taylor, 1 9 7 1 ), the mycoflora associated with early land plants is known almost entirely from silicified specimens in the Rhynie Chert (Kidston and Lang, 1921; Harvey, Lyon, and Lewis, 1969; Boullard and Lemoigne, 1971 Illman, 1984) and similar calcified materiai from the Gaspe Peninsula (Stubblefield and Banks, 1983). In the present paper an additional occurrence of Devonian fungi is documented. An extensive fungal infection is described in the tracheids and ray cells of the Upper Devonian progymnosperm Callixylon newberryi (Dawson) Elkins and Wieland. Hyphae were first noted in this material by Arnold (1931), who published a single light micrograph of infected tracheids during the course of an anatomical investigation of Callixylon newberryi. Reinvestigation of material from this locality offers the opportunity to study both the earliest known fungi in wood as well as the ' Received for publication 3 December 1984, revision accepted 14 June 1985. The authors with to thank Dr. Roland L. Seymour of the Department of Botany, The Ohio State UniversityColumbus, and Dr. Robert L. Shaffer of the Herbarium The University of Michigan-Ann Arbor for much usefui discussion. This research was supported in part by funds from the NSF (DEB-8213060). We wish to dedicate this paper to our colleague, the late Dr. Charles E. Miller of Ohio University, Athens, OH who worked closely with us in several studies on fossil fungi. Chuck Miller's cherished friendship, and his enthusiasm and in-depth understanding of fungi will continue to serve as an inspiration for our work. earliest known example of wood decay caused by fungi, and also suggests the presence of higher fungi in the Upper Devonian. MATERIALS AND METHODS-Fungi occur in the secondary xylem of a block of silicified Callixylon newberryi collected S mi northeast of Henryville, Clark County, IN. The fragment of wood comes from the upper portion of the Blackiston Formation in the New Albany Shale. This part of the formation is Upper Devonian in age and corresponds to the European Famennian stage (Collinson, 1967). The specimen is no. 13834 in the Museum of Paleontology, The University of Michigan-Ann Arbor. Peels and thin sections from this specimen bear nos. 13834-1 to 13834-20 in the same collection. Material was prepared for light microscopy both as ground thin sections and as cellulose acetate peels in which concentrated hydrofluoric acid was substituted for hydrochloric acid. In preparation for scanning electron microscopy (SEM), specimens were etched for 24 min with concentrated hydrofluoric acid and rinsed in water until neutral. Material was then dried in a critical point dryer, mounted on standard stubs, and coated with both carbon and gold. The use of carbon significantly reduced charging (Skog, 1983). DESCRIPTION-The infected specimen is a block of secondary xylem approximately 100 cm3 in size from the progymnosperm Callixylon newberryi. Due to the fragmentary nature