Elemental Composition of Clastoderma Debaryanum Stalks

Abstract

Clastoderma debaryanum A. Blytt, a myxomycete which commonly develops in moist chamber cultures on bark from living trees, is cosmopolitan in distribution. In many collections of this organism a characteristic amber-like swelling is encountered midway along the stalk. The stalk swelling is a variable character in that collections which key to C. debaryanum sometimes lack this structure (Martin and Alexopoulos, 1969). The original description of C. debaryanum by Blytt in 1880, made no mention of this swelling, but this structure has been found so often by subsequent collectors that it has come to be thought of as being characteristic of the species. We undertook to characterize the elemental composition of sporangial stalks, with and without swellings. Sporangia of C. debaryanum were obtained from the University of Texas Myxomycete Collection (UTMC), The New York Botanical Garden (NYBG), and the National Fungus Collections (BPI). A total of 24 collections were examined from widely scattered geographical areas. Elemental composition was determined with a Kevex model 5100 energy dispersive X-ray spectrometer attached to an AMR 1000A scanning electron microscope. A single sporangium from each collection was mounted on an aluminum stub with double sticky tape. Specimens were coated with carbon and gold-palladium in a Denton high vacuum evaporator. X-ray counts were collected with a 200 sec probe at 30 kV, magnification x 1000, with minimum partial field settings. Spot size was maintained at a constant value and the specimen was held at a tilt of 45? with respect to the detector. Three spectra were obtained from each stalk; one spectrum from the swelling or region of the stalk where the swelling is typically located, a second from a region just above the base of the stalk, and a third from the upper portion of the stalk just below the sporangium. Spectra were smoothed and submitted to background subtraction. Elemental peaks for aluminum, gold, and palladium which were introduced during sample preparation were stripped from the spectra. X-ray counts were recorded for each elemental peak and normalized with respect to a total of 171,982 counts, which was the highest figure obtained with a 200 sec probe. The stalks of C. debaryanum sporangia vary morphologically in that some stalks evenly taper from the base toward the sporangium (FIG. 2) while others possess globular or oval swellings midway along the stalk (FIG. 1). Fusiform swellings which are much less prominent than the swellings depicted in FIG. I are also frequently encountered. X-ray spectra of C. debaryanum stalks consistently revealed the presence of calcium and chlorine (FIGS. 5-10). Sulphur, potassium, and iron were also frequently encountered in measurable quantities. Traces of magnesium, phosphorus,