Fertile Prototaxites taiti: a basal ascomycete with inoperculate, polysporous asci lacking croziers

The affinities of Prototaxites have been debated ever since its fossils, some attaining tree-trunk proportions, were discovered in Canadian Lower Devonian rocks in 1859. Putative assignations include conifers, red and brown algae, liverworts and fungi (some lichenised). Detailed anatomical investigation led to the reconstruction of the type species, P. logani, as a giant sporophore (basidioma) of an agaricomycete (= holobasidiomycete), but evidence for its reproduction remained elusive. Tissues associated with P. taiti in the Rhynie chert plus charcoalified fragments from southern Britain are investigated here to describe the reproductive characters and hence affinities of Prototaxites Thin sections and peels (Pragian Rhynie chert, Aberdeenshire) were examined using light and confocal microscopy; Přídolí and Lochkovian charcoalified samples (Welsh Borderland) were liberated from the rock and examined with scanning electron microscopy. Prototaxites taiti possessed a superficial hymenium comprising an epihymenial layer, delicate septate paraphyses, inoperculate polysporic asci lacking croziers and a subhymenial layer composed predominantly of thin-walled hyphae and occasional larger hyphae. Prototaxites taiti combines features of extant Taphrinomycotina (Neolectomycetes lacking croziers) and Pezizomycotina (epihymenial layer secreted by paraphyses) but is not an ancestor of the latter. Brief consideration is given to its nutrition and potential position in the phylogeny of the Ascomycota.This article is part of a discussion meeting issue 'The Rhynie cherts: our earliest terrestrial ecosystem revisited'.

New insights into the evolutionary history of Fungi from a 407 Ma Blastocladiomycota fossil showing a complex hyphal thallus

Zoosporic fungi are key saprotrophs and parasites of plants, animals and other fungi, playing important roles in ecosystems. They comprise at least three phyla, of which two, Chytridiomycota and Blastocladiomycota, developed a range of thallus morphologies including branching hyphae. Here we describe Retesporangicus lyonii gen. et sp. nov., an exceptionally well preserved fossil, which is the earliest known to produce multiple sporangia on an expanded hyphal network. To better characterize the fungus we develop a new method to render surfaces from image stacks generated by confocal laser scanning microscopy. Here, the method helps to reveal thallus structure. Comparisons with cultures of living species and character state reconstructions analysed against recent molecular phylogenies of 24 modern zoosporic fungi indicate an affinity with Blastocladiomycota. We argue that in zoosporic fungi, kinds of filaments such as hyphae, rhizoids and rhizomycelium are developmentally similar structures adapted for varied functions including nutrient absorption and anchorage. The fossil is the earliest known type to develop hyphae which likely served as a saprotrophic adaptation to patchy resource availability. Evidence from the Rhynie chert provides our earliest insights into the biology of fungi and their roles in the environment. It demonstrates that zoosporic fungi were already diverse in 407 million-year-old terrestrial ecosystems.This article is part of a discussion meeting issue 'The Rhynie cherts: our earliest terrestrial ecosystem revisited'.

Phylogenetic analysis of LSU and SSU rDNA group I introns of lichen photobionts associated with the genera Xanthoria and Xanthomendoza (Teloschistaceae, lichenized Ascomycetes)

We studied group I introns in sterile cultures of selected groups of lichen photobionts, focusing on Trebouxia species associated with Xanthoria s. lat. (including Xanthomendoza spp.; lichen-forming ascomycetes). Group I introns were found inserted after position 798 (Escherichia coli numbering) in the large subunit (LSU) rRNA in representatives of the green algal genera Trebouxia and Asterochloris. The 798 intron was found in about 25% of Xanthoria photobionts including several reference strains obtained from algal culture collections. An alignment of LSU-encoded rDNA intron sequences revealed high similarity of these sequences allowing their phylogenetic analysis. The 798 group I intron phylogeny was largely congruent with a phylogeny of the Internal Transcribed Spacer Region (ITS), indicating that the insertion of the intron most likely occurred in the common ancestor of the genera Trebouxia and Asterochloris. The intron was vertically inherited in some taxa, but lost in others. The high sequence similarity of this intron to one found in Chlorella angustoellipsoidea suggests that the 798 intron was either present in the common ancestor of Trebouxiophyceae, or that its present distribution results from more recent horizontal transfers, followed by vertical inheritance and loss. Analysis of another group I intron shared by these photobionts at small subunit (SSU) position 1512 supports the hypothesis of repeated lateral transfers of this intron among some taxa, but loss among others. Our data confirm that the history of group I introns is characterized by repeated horizontal transfers, and suggests that some of these introns have ancient origins within Chlorophyta.

Bacterial epibionts and endolichenic actinobacteria and fungi in the Lower Devonian lichen Chlorolichenomycites salopensis

The charcoalified fragment of the dorsiventrally organized, internally stratified presumed green algal lichen Chlorolichenomycites salopensis from the Lower Devonian Lochkovian strata in the Welsh Borderland carries bacterial colonies on the upper surface, i.e. the cortex, and actinobacterial filaments in the medulla underneath the photobiont layer. Moreover relatively thin hyphae of presumed endolichenic fungi were found. As in extant lichens, which are best regarded as consortia with an unknown number of participants, this internally stratified, fossil thallus fragment of a presumed green algal lichen harbours a diverse microbial community.

The earliest records of internally stratified cyanobacterial and algal lichens from the Lower Devonian of the Welsh Borderland

Lichenization is assumed to be a very ancient mode of fungal nutrition, but fossil records are rare. Here we describe two fragments of exceptionally preserved, probably charred, lichen thalli with internal stratification. Cyanolichenomycites devonicus has a cyanobacterial and Chlorolichenomycites salopensis a unicellular, presumably green algal photobiont. Fruiting bodies are missing. Cyanolichenomycites devonicus forms asexual spores in a pycnidium. All specimens were examined with scanning electron microscopy techniques. The fossils were extracted by maceration. Extant lichens and free-living cyanobacteria were either experimentally charcoalified for comparison or conventionally prepared. Based on their septate hyphal structure, both specimens are tentatively interpreted as representatives of the Pezizomycotina (Ascomycota). Their presence in 415 million yr (Myr) old rocks from the Welsh Borderland predates existing Late Cretaceous records of pycnidial conidiomata by some 325 Myr and Triassic records of lichens with broadly similar organization by some 195 Myr. These fossils represent the oldest known record of lichens with symbionts and anatomy as typically found in morphologically advanced taxa today. The latter does not apply to Winfrenatia reticulata, the enigmatic crustose lichen fossil from the Lower Devonian, nor to presumed lichen-like organisms such as the Cambrian Farghera robusta or to the Lower Devonian Spongiophyton minutissimum.

Earliest fossil record of bacterial-cyanobacterial mat consortia: the early Silurian Passage Creek biota (440 Ma, Virginia, USA)

Cyanobacteria in terrestrial and aquatic habitats are frequently associated with heterotrophic bacteria, and such associations are most often metabolically interactive. Functionally, the members of such bacterial-cyanobacterial consortia benefit from diverse metabolic capabilities of their associates, thus exceeding the sum of their parts. Such associations may have been just as ubiquitous in the past, but the fossil record has not produced any direct evidence for such associations to date. In this paper, we document fossil bacteria associated with a macrophytic cyanobacterial mat in the early Silurian (Llandovery) Massanutten Sandstone of Virginia, USA. Both the bacterial and the cyanobacterial cells are preserved by mineral replacement (pyrite subsequently replaced by iron oxyhydroxides) within an amorphous carbonaceous matrix which represents the common exopolysaccharide investment of the cyanobacterial colony. The bacteria are rod-shaped, over 370 nm long and 100 nm in diameter, and occur both as isolated cells and as short filaments. This occurrence represents the oldest fossil evidence for bacterial-cyanobacterial associations, documenting that such consortia were present 440 Ma ago, and revealing the potential for them to be recognized deeper in the fossil record.

Fine structure and phylogeny of green algal photobionts in the microfilamentous genus Psoroglaena (Verrucariaceae, lichen-forming ascomycetes)

According to the literature the microfilamentous thalli of lichen-forming ascomycetes of the genus Psoroglaena are assumed to harbour vivid green "prochlorophyte" cyanobacterial photobionts. As this would be the first report of terrestrial "prochlorophytes" we investigated the fine structure and two molecular markers (SSU rDNA and rbcL) of the photobionts of P. stigonemoides (Orange) Henssen and P. epiphylla Lücking. Both Psoroglaena spp. had unicellular green algal photobionts, representatives of the Trebouxiophyceae. The photobiont of P. stigonemoides is closely related to the non-symbiotic auxenochlorella protothecoides and to a Chlorella endosymbiont of the freshwater polyp Hydra viridis. The putative photobiont of P. epiphylla may be related to Chlorella luteoviridis, C. saccharophila, and a Pseudochlorella isolate. In contrast to other microfilamentous lichens, which derive their shape from filamentous green algae or cyanobacterial colonies overgrown and ensheathed by the fungal partner, Psoroglaena mycobionts position their unicellular photobiont in uni- or multiseriate rows which strongly resemble the situation in filamentous cyanobacterial colonies.

Interactions of sterile-cultured lichen-forming ascomycetes with asbestos fibres

Sterile cultured isolates of lichen-forming ascomycetes have not yet been used to investigate mycobiont-mineral substrate interactions under controlled conditions. In this study Candelariella vitellina, Xanthoparmelia tinctina and Lecanora rupicola mycobionts were isolated and inoculated with chrysotile fibres in the laboratory, in order to verify whether physical and chemical weathering processes, which were already described in the field, may be reproduced in vitro. Tight adhesion of hyphae to chrysotile fibres was observed in all species. The adhering hyphae affected the chemical composition of asbestos fibres, with the selective depletion of magnesium being a prominent feature, as is the case in field conditions. Oxalic acid and pulvinic acid, mycobiont-derived metabolites of X. tinctina and C. vitellina, were involved in the weathering action. Time and environmental factors and the absence of biological synergisms strongly limited the chemical weathering in vitro compared with what was observed in the field. Nevertheless, the results show that in vitro incubation of sterile-cultured lichen-forming fungi with minerals is a practicable experimental system to investigate the weathering effects of different mycobionts and fungal compounds under controlled conditions.

Mating systems in representatives of Parmeliaceae, Ramalinaceae and Physciaceae (Lecanoromycetes, lichen-forming ascomycetes)

The progeny of meiosis of eight Parmeliaceae, two Ramalinaceae and seven Physciaceae were subjected to fingerprint analysis using RAPD-PCR applied to single spore isolates. The sample set included common and widespread rarely fertile species (Parmelia sulcata, Pseudevernia furfuracea, Physcia tenella), local to common, infrequently fertile species (Melanelixia glabra, Parmelina tiliacea, Xanthoparmelia conspersa, X. stenophylla, Anaptychia runcinata, Diploicia canescen, Physconia distorta), local to rare, infrequently or regularly fertile species with declining distributions (Parmelina carporrhizans, P. quercina, Ramalina fastigiata, R. fraxinea, Anaptychia ciliaris), and local to common, regularly fertile species (Physcia aipolia, P. stellaris). All species turned out to be heterothallic, polymorphisms among RAPD markers ranging from 10-87%. The significance of these findings for population genetics and conservation biology, and potential reasons for infrequent ascoma formation in some of the species are discussed.

Characterisation of the mating-type locus in the genus Xanthoria (lichen-forming ascomycetes, Lecanoromycetes)

Conserved regions of mating-type genes were amplified in four representatives of the genus Xanthoria (X. parietina, X. polycarpa, X. flammea, and X. elegans) using PCR-based methods. The complete MAT locus, containing one ORF (MAT1-2-1) coding for a truncated HMG-box protein, and two partial flanking genes, were cloned by screening a genomic lambda phage library of the homothallic X. parietina. The flanking genes, a homologue of SLA2 of Saccharomyces cerevisiae and a DNA lyase gene, served to amplify the two idiomorphs of the X. polycarpa MAT locus. Each idiomorph contains a single gene: MAT1-2-1 codes for a HMG-box protein, MAT1-1-1 encodes an alpha domain protein. The occurrence of mating-type genes in eight single spore isolates derived from one ascus was studied with a PCR assay. In the homothallic X. parietina a HMG fragment, but no alpha box fragment was found in all isolates, whereas in X. elegans, another homothallic species, all tested isolates contained a fragment of both idiomorphs. Conversely, isolates of the heterothallic X. polycarpa contained either a HMG or an alpha box fragment, but never both.

Mating systems in the genus Xanthoria (lichen-forming ascomycetes)

Genetic variability among sterile cultured single ascospore isolates of Xanthoria parietina, X. calcicola, X. ectaneoides, X. capensis, X. polycarpa and X. resendei was investigated with RAPD-PCR. If available five out of eight ascospores per ascus were analysed. In some samples multispore and mycelial isolates from ascomata were included in the analysis. Ascospore germination rates and phenotypic features such as growth rate, pigmentation and secondary metabolites were uniform in X. parietina sporelings of the same ascus, but varied among the progeny of meiosis in all other species. Phenotypic features correlated with genetic variability. X. parietina revealed polymorphisms among specimens from different worldwide locations. In contrast nine out of ten sets of sibling spores were genetically uniform, with only 2% polymorphism in the remaining set, indicating that X. parietina might be homothallic. X. calcicola, X. ectaneoides, X. capensis, X. polycarpa and X. resendei revealed 9-66% polymorphic loci and therefore are considered heterothallic.

Insect-mediated reproduction of systemic infections by Puccinia arrhenatheri on Berberis vulgaris

• Witches' brooms on Berberis vulgaris are induced by a systemically infecting rust fungus, Puccinia arrhenatheri. These witches' brooms bear yellow discolored leaves on which the fungus exposes its gametes in a sugary nectar. During the spermatial stage of the fungus the infected leaves emit a strong, flowery scent. • An exclusion-experiment was used to evaluate whether fungal reproductive success, defined by the ability of the fungus to produce aeciospores, depended on gamete transfer by insects. To determine whether insects were attracted to the infected leaves, and if so, why, visitation to infected and uninfected leaves was quantified and volatiles produced by leaves, infected leaves and flowers were analyzed. • The production of aeciospores was significantly higher on witches' brooms with insect visitation. Visitation rates were higher and visits were longer on witches' brooms than on uninfected branches. A wide diversity of visitors, mainly Diptera and Hymenoptera, was observed. The volatiles emitted by infected leaves were composed of sweet floral fragrances and insect pheromones. • Our results suggest that sexual reproduction of the pathogen requires out-crossing by insects and that infected leaves attract insects by floral mimicry (bright yellow color and the production of sugary nectar and volatiles).

Hydrophobins DGH1, DGH2, and DGH3 in the lichen-forming basidiomycete Dictyonema glabratum

Dictyonema glabratum is a lichen-forming basidiomycete whose symbiotic phenotype shares similarities to both lichens and its non-lichen-forming relatives. In the photobiont layer of D. glabratum intercellular gas-filled spaces are present even when the lichen is water-saturated. The walls of hyphae lining air cavities are covered by a hydrophobic, rodlet-patterned layer, assumed to be formed by hydrophobins. Hot SDS-insoluble, but trifluoroacetic acid-soluble lichen cell wall extracts contained seven proteins. The N-terminal sequence of the most abundant 14-kDa protein was used to carry out cDNA cloning by RT-PCR. The deduced amino acid sequence of the amplified fragment encoded a class I hydrophobin, called DGH1. The cDNA sequence encoding the signal peptide was cloned by RACE-PCR, which also coamplified cDNA fragments encoding two additional class I hydrophobins, DGH2 and DGH3. The three proteins share 54 to 66% amino acid identity. The D. glabratum hydrophobin extract containing either all proteins or primarily DGH1 self-assembled and formed a rodlet mosaic similar to the one observed in situ. Concentration of the protein extract was shown to influence the length of the self-assembled rodlets.

Alterations of lipolytic enzymes and high-density lipoprotein subfractions induced by physical activity in type 2 diabetes mellitus

OBJECTIVE

This study investigates the effects of regular moderate physical activity on lipolytic enzymes and plasma lipid concentration, particularly high-density lipoprotein cholesterol (HDL-C) subfractions, in patients with type 2 diabetes mellitus.

DESIGN

Ten patients participated in a 3-month exercise programme without any changes in current medical therapy. The control group consisted of six patients who were matched with regard to sex, age, diabetes duration and diabetes therapy.

RESULTS

Mean (+/- SE) physical activity in the intervention group increased from 70 +/- 21 to 220 +/- 28 min per week, which resulted in an increase in total HDL-C from 1.04 +/- 0.07 to 1.28 +/- 0.12 (P < 0.001). The HDL3-C subfraction increased from 0.71 +/- 0.08 to 0.86 +/- 0.08 mM (P = 0.01) with no significant changes in the HDL2-C subfraction (0.33 +/- 0.04 vs. 0.42 +/- 0.05). These changes were paralleled by an 85% increase in hepatic lipase (HL) activity, from 25.7 +/- 5.1 to 47.4 +/- 4.9 micromol x mL(-1) x h(-1) (P < 0.001) and a 45% increase in lipoprotein lipase (LPL) activity, from 16.8 +/- 3.0-24.3 +/- 2.7 micromol x mL(-1) x h(-1) (P = 0.01). Lecithin-cholesterol acyl-transferase (LCAT) activity increased by 32%, from 156 +/- 26 to 206 +/- 32 nmol x mL(-1) x h(-1) (P < 0.001). In the control group there were no significant changes in any of the variables assessed.

CONCLUSIONS

Regular moderate physical activity in patients with type 2 diabetes led to an overall increase in HL, LPL, and LCAT. HL showed a more pronounced increase than LPL and LCAT. The changes in lipolytic and transferase enzyme pattern resulted in a significant increase of plasma HDL-C, mainly of the HDL3-C subfraction.

Interfacial self-assembly of fungal hydrophobins of the lichen-forming ascomycetes Xanthoria parietina and X. ectaneoides

In the symbiotic phenotype of the lichen-forming ascomycetes Xanthoria parietina and X. ectaneoides, a conglutinate, hydrophilic cortex surrounds a system of aerial hyphae with hydrophobic wall surfaces. In X. parietina freeze-fracture electron microscopy showed that a rodlet layer covers the fungal and algal wall surfaces. Extracts of hot SDS-insoluble wall residues isolated from both species contained a protein that revealed a rodlet layer upon interfacial self-assembly. The N-terminal sequence of the 10-kDa protein of X. ectaneoides served to clone cDNA fragments of XEH1 (H1 of X. ectaneoides) and XPH1 (H1 of X. parietina) by RT-PCR. Genomic DNA blot analysis with both lichenized species and the aposymbiotically cultured symbionts of X. parietina showed that XPH1 and XEH1 are fungal single copy genes. The deduced amino acid sequences of the two encoded proteins were 96% identical and showed the characteristics of class I hydrophobins.

[Risks and side effects of intensified insulin therapy]

Diabetes mellitus may be accompanied by severe long-term microvascular, neurological and macrovascular complications. Prevention of these complications represents an enormous challenge for the diabetic patients and their doctors. However, if diabetic long-term complications occur, affecting one or more organ systems, it is a major goal to prevent their progression. Both, primary and secondary prevention require a good metabolic control striving for near-normal blood glucose values. Intensified insulin therapy (three or more daily injections or external insulin pump) has been shown to achieve a glycemic control as close to the normal range as possible.

Experimental studies with foliose macrolichens: fungal responses to spatial disturbance at the organismic level and to spatial problems at the cellular level during drought stress events

Improved culture methods and the application of cryotechniques in light and electron microscopy have allowed new insights at the organismic and cellular levels in mycobiont–photobiont relations of selected lichen species. Growth, regenerative capacity, and the ability to cope with spatial disturbances were tested in the foliose macrolichens Xanthoria parietina and Parmelia sulcata. These mycobionts can sense and partly correct an inverted position and thus insure adequate illumination for the photobiont cell population. In both taxa, the apical/marginal pseudomeristem and adjacent elongation zone bend backwards. Parmelia sulcata continues this bending process and grows arch-like until its margin reaches the substratum. Xanthoria parietina stops bending and growing but regenerates new primordial stages along the marginal rim and cut edges. These primordia develop into new lobes with a normal upside up topography. Its remarkable regenerative capacity permits X. parietina to develop a new rosette from an assembly of minute thallus fragments that had been fixed to a ceramic substratum. Cryotechniques applied at the light and electron microscopy levels allow us to visualize drought stress induced structural alterations at the cellular level in lichen bionts. Neither partner of the symbiosis plasmolyses under extreme drought stress. The globose to ovoid green algal or cyanobacterial photobiont cells and their walls shrivel dramatically but the fungal cell wall cannot be deformed to such a high degree during stress events. Ascomycetous lichen mycobionts of three different orders formed a large, intracellular gas bubble of unknown ontogeny and content when their turgor pressure dropped to very low values. This cytoplasmic "air bag" allows the protoplast to shrink and, at the same time, to keep the cell membrane in contact with the wall. In the desiccated state many lichens tolerate extreme stress conditions. Thallus fragments of dry X. parietina grew normally after having been cryofixed in subcooled liquid nitrogen, sputter coated, and examined in a low temperature scanning electron microscope. Fully hydrated samples did not survive this treatment. Key words: culturing experiments, regenerative capacity, drought stress, LTSEM, freeze substitution, intracellular gas bubble.

Developmental biology of lichens

Lichen-forming fungi are a large, taxonomically diverse group of nutritional specialists which acquire fixed carbon from a population of minute green algal or cyanobacterial cells. Mycobionts of foliose or fruticose lichens differ from the rest of the fungi by expressing morphologically and anatomically complex symbiotic phenotypes. The extracellularly located photobiont cell population of these macrolichens is housed and controlled by the quantitatively predominant fungal partner which competes for space above ground, secures adequate illumination and facilitates gas exchange. This review summarizes data on the ontogeny, functional morphology, growth patterns and internal thalline differentiation of macrolichens. Contents Summary 659 I. Introduction 659 II. Establishment of the lichen symbiosis 662 III. Growth and cell turnover 669 IV. Outlook 674 Acknowledgements 674 References 674.

[The difficult neurotic patient from the psychiatrist's viewpoint]

Neurotic applicants for an infirmity-pension belong to the group of problem patients for attending general practitioners and specialists alike. The doctor-patient relationship is often disturbed. The source of the article emanates from problematic relationships. It is described how the psychiatrist deals with the difficulties in the expertise situation, where he attempts to gain insight into the personality structure. Furthermore, psychodynamics of a frequent personality structure of neurotic invalids are described. Finally, reference to literature is introduced and discussed.

Chemical and ultrastructural studies on the distribution of sporopolleninlike biopolymers in six genera of lichen phycobionts

Cell walls of cultured lichen phycobionts of the genera Coccomyxa, Elliptochloris, Myrmecia, Pseudochlorella, Trebouxia, and Trentepohlia were investigated with cytological and chemical methods with regard to the presence or absence of trilaminar sheaths and (or) resistant biopolymers. Trilaminar cell wall layers occurred in Coccomyxa, Elliptochloris, Myrmecia, and (less distinctly) Pseudochlorella species. A biopolymer highly resistant to nonoxidative degradation by phosphoric acid occurred only in the isolated and vigorously extracted cell walls of Coccomyxa and Elliptochloris species. The walls of all the other phycobionts, including Myrmecia and Pseudochlorella, were totally degraded, showing that a trilaminar wall layer is not conclusive evidence for the presence of a resistant cell wall polymer. The infrared absorption spectra of the degradation-resistant cell wall polymer of Coccomyxa and Elliptochloris species were not fully identical with those of natural sporopollenins. When the widely used, but chemically less appropriate acetolysis method was applied to either entire cells or isolated but not fully extracted cell walls of Coccomyxa, Elliptochloris, Myrmecia, Pseudochlorella, Trebouxia, and Trentepohlia species, they all yielded acetolysis-resistant residues whose infrared spectra resembled natural sporopollenin.

Ultrastructural studies on conidiomata, conidiophores, and conidiogenous cells in six lichen-forming Ascomycetes

The conidiomata, conidiophores, and conidia of six lichen-forming Ascomycetes were investigated using the scanning electron microscope, and conidium development in two of these species was studied by transmission electron microscopy. Phialidic (micro) conidium formation was observed in the mycobiont of Parmelia tiliacea, Physconia pulverulacea, and Cladonia furcata (Lecanorales), in Lobaria laetevirens (Peltigerales), and in Caloplaca aurantia (Teloschistales). Annellations, first described by Vobis on the basis of light and transmission electron microscope investigations, were also found in scanning electron microscope preparations of macroconidia bearing conidiogenous cells of Lecanactis abietina (Opegraphales). Ultrastructural and developmental studies on conidiophore structure and conidium formation may be of interest for taxonomic and evolutionary considerations in lichen-forming fungi.

Sporopollenin in the cell walls of Coccomyxa and Myrmecia phycobionts of various lichens: an ultrastructural and chemical investigation

Symbiotic and cultivated Myrmecia phycobionts of Baeomyces rufus and Coccomyxa phycobionts of five different asco- and basidio-lichens were investigated with cytological and chemical methods. The cell wall structure of the free-living type species Coccomyxa dispar was compared with that of the lichen phycobionts.Three different wall layers were observed in all Coccomyxa and Myrmecia cells investigated. An innermost, variably thick layer is amorphous in structure and is built up mainly by Golgi-derived hemicelluloses. An outer wall layer, uniformly thick, appears electron dense in thin sections and exhibits short, probably cellulosic fibrils embedded in an amorphous matrix in freeze-fracture preparations. Beyond these two wall layers is an outermost trilaminar wall layer of uniform thickness in all species investigated. It contains sporopollenin in its electron-transparent, rigid middle part; proteinlike particles are embedded in an amorphous, carbohydrate-containing matrix on its electron-dense inner and outer surfaces. IR spectrophotometry of acetolysis-resistant material yielded data comparable with those of other sporopollenin-containing algal walls, although the Coccomyxa and Myrmecia sporopollenin did not dissolve in chromic acid. The trilaminar layer is not lysed during or after autospore formation. Persistent mother cell walls were detected in all lichen thalli investigated, as well as in the culture medium of isolated phycobionts. Persistent mother cell walls were also found in the gelatinous sheath of Coccomyxa dispar.This type of wall structure affords protection against fungal parasitism and may be a significant factor in the success of some lichens and some other symbiotic systems.