This ultrastructural investigation of Trypethelium eluteriae, an endoperidermal lichen, reveals an amorphous upper cortex devoid of cork cells previously unreported for the Trypetheliaceae. The cells of the phycobiont, Trentepohlia, possess bilamellar cell walls, large parietal chloroplasts with interthylakoidal starch grains and haematochrome droplets located around the periphery of the cells. The ascomycetous mycobiont has variably thick walls; the thinnest walls are found in the medullary hyphae associated with periderm cells. The mycobiont cells possess the normal complement of organelles. The mycobiont plasmalemma is relatively smooth in those hyphae of the upper cortex and algal layers but in the medullary hyphae, the plasmalemma has extensive invaginations. The amorphous upper cortex, thin medullary hyphal walls and the plasmalemma invaginations suggest a saprophytic relationship between the mycobiont and periderm cells. Algal-fungal contact is of the appressorium type possibly reflecting either the mesic habitat of the lichen or its evolutionary status. Trypethelium eluteriae Spreng. is a tropical-subtropical endoperidermal crustose lichen. The thallus grows entirely within the periderm with only the perithecia emerging from the bark surface. The ultrastructural aspects of endolithic lichens have been investigated (Kushnir & Galun 1977), but to date no ultrastructural analysis of endoperidermal lichens has been published. Likewise, only one lichen with Trentepohlia as a phycobiontChiodecton sanguineum (Swartz) Vain. (Ellis 1975)-has been studied ultrastructurally. This paper is a report on the ultrastructure of T. eluteriae. MATERIALS AND METHODS Collections of Trypethelium eluteriae Spreng. were made from bark of living trees of Carpinus caroliniana Walt. at the Louisiana State University Burden Research Plantation in Baton Rouge, Louisiana. Specimens for transmission electron microscopy were fixed either in aqueous 2% KMnO4 at room temperature for one hour (Mollenhauer 1959) or in 4% glutaraldehyde in 0.2 M s-collidine buffer (pH 7.4) at room temperature for 15 minutes followed by an equal volume of 2% osmium tetroxide in 0.2 M s-collidine buffer (pH 7.4) added at 4?C for 45 minutes (Bennett & Luft 1959). The glutaraldehydeosmium-fixed material was stained en bloc with 0.5% uranyl acetate. The fixed material was dehydrated in a graded acetone series and embedded in Epon-Araldite plastic (Mollenhauer 1963). Both monitor and ultrathin sections were cut on a Porter-Blum MT-2 ultramicrotome with glass or diamond knives. The monitor sections were stained with methylene blue (Postek & Tucker 1976), observed and photographed under brightfield or phase contrast illumination with a Leitz Orthoplan microscope 1 Present address: Department of Botany, Miami University, Oxford, OH 45056. 0007-2745/80/170-178$ 1. 10/0 This content downloaded from 207.46.13.21 on Mon, 11 Apr 2016 12:33:14 UTC All use subject to http://about.jstor.org/terms 1980] LAMBRIGHT & TUCKER: ULTRASTRUCTURE OF TRYPETHELIUM 171 and Orthomat camera. The ultrathin sections were mounted on uncoated grids, observed and photographed with a Hitachi HU-11A electron microscope at 75 kV.