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LICHENS GROWING ON GLASS IN ANTARCTICA
Lichenologist 28(4): 385–390 (1996)
LICHENS GROWING ON GLASS IN ANTARCTICA B. SCHROETER* and L. G. SANCHO‡
Abstract: Early stages of lichen colonization on glass are reported for the first time from Antarctica. In the initial establishment of the lichen thallus rhizomorphs play an important role for the attachment to the substratum and the exploitation of nutrient and photobiont resources. The micrographs presented indicate that in Antarctica colonization of bare substrata by lichens is not necessarily an extremely slow process. Furthermore, our findings demonstrate that the use of artificial substrata such as glass could provide a simple method for studies in lichen colonization and development in extreme environments. ? 1996 The British Lichen Society
Introduction The lichen symbiosis is able to colonize a great variety of substrata. Besides natural substrata lichens grow also on man-made substrata derived from plant or animal sources such as cork, bones or leather (Brightman & Seaward 1978), synthetic material such as plastic tape (Sipman 1994), substrata derived from mineral sources such as bricks, cement, concrete roofs and walls, and glass and iron amongst others (Green & Snelgar 1977; Brightman & Seaward 1978). Vitricolous lichens can be of special interest because their smooth and often datable substratum may allow an accurate assessment of lichen growth rates (Armstrong 1975). Lichens growing on glass have been reported since the 19th century, predominantly from church windows in Europe (see Brightman & Seaward 1978), and several papers discuss a possible role of lichens in the deterioration of stained glass (see Mellor 1923). In favourable climates fast-growing species such as Parmelia scabrosa occur on glass surfaces of greenhouses and even on the windscreens of scrapped cars in New Zealand (Green & Snelgar 1977). In contrast, the extreme environmental conditions prevent comparable growth of lichens in Antarctica (see Kappen 1993; Schroeter et al. 1995). However, there is only a little information concerning the initial establishment and development of lichens in polar regions (Fahselt et al. 1988; Fahselt & Sweet 1991). Under Antarctic conditions, stability of the substratum seems to be one of the more important factors for lichen colonization. Therefore, it was unexpected to discover lichens growing on small pieces of broken glass on Livingston Island, maritime Antarctica, in January 1993. The small pieces of glass were partly covered with a network of hyphae and some small lichen areoles with algal cells, indicating early stages in the development of lichen thalli. *Botanisches Institut, Universität Kiel, Olshausenstraße 40, D-24098 Kiel, Federal Republic of Germany. ‡Departamento de Biologı´a Vegetal II, Facultad de Farmacia, Universidad Complutense, E-28040 Madrid, Spain. 0024–2829/96/040385+06 $18.00/0
? 1996 The British Lichen Society
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THE LICHENOLOGIST
Vol. 28
Site Description and Methods Broken pieces of transparent glass were found in the vicinity of the Spanish Antarctic base BAE Juan Carlos I (62)40*S, 60)23*W) on Livingston Island, South Shetland Islands, maritime Antarctica, in January 1993. Broken glass of different sizes (from less than 0·5 cm2 up to 10 cm2) was distributed on the top of a boulder that was sparsely covered with Usnea antarctica and U. aurantiaco-atra. More pieces of broken glass were found on the ground nearby together with rusted tins, and partly covered by pyroclastic material. The pieces of glass originated from transparent bottles similar to Coca Cola bottles or bottles containing mineral water. Only a small part of the glass pieces showed signs of fungal/lichen colonization. Specimens were macroscopically and microscopically examined using a photomacroscope (Wild M400, FRG), a light microscope (Zeiss Jenaval, FRG) and a scanning electron microscope (Zeiss DSM-960, FRG) according to Valladares et al. (1994).
Results and Discussion Most of the early stages of colonization observed on the small pieces of glass were fungi and made up of dark-pigmented branched mycelial strands, occasionally developing young lichenized squamules (Figs 1A & 2A). The squamules always contained several algal cells (Trebouxia type) enveloped by mycobiont hyphae (Fig. 1C). The presence of lichenized algae clearly indicates that the samples represent initial stages in the development of a lichen. The hyphae probably started from ascospores, which were relatively frequent between them (Fig. 2C), whereas vegetative diaspores were not present. It is known that the development of new thalli can be as rapid from vegetative diaspores as from ascospores (Ott 1987a,b). The mycelial strands were multihyphal linear aggregates, the terminal cells of which were quite elongated and not pigmented (Fig. 1B), probably indicating apical extension. This concurs very well with the concept that lichen rhizomorphs are a form of specialized hypothallus (Malone 1977; Wagner & Letrouit-Galinou 1988; Sanders & Rico 1992; Sanders 1994). Furthermore, as in the case of typical rhizomorphs (first described by Bachmann 1890), the mycelial strands growing on the Antarctic glass are well-integrated fascicles of hyphae in a common intercellular gelatinous matrix, rather than a loose association of hyphae (Fig. 2B). In lichens a gelatinous matrix not only facilitates early physical contacts between the bionts and glues hyphae into compact layers (Ahmadjian 1993) but also permits attachment to the substratum, as was observed in some cases (Fig. 2D). Colonization of the substratum always started in areas with a deteriorated surface, that is, with cracks and fissures that result from the break up of the glass bottles. A damaged surface seems to allow a much better attachment of the hyphae to the substratum. This was also true for the colonization of church windows where lichens were found only F. 1. Lichens on glass. A, Early stages of lichen colonization of glass. Mycelial strands growing on a small piece of glass. The dark-pigmented fungal branches are preferentially attached to small fissures in the glass but also extend over smooth areas. B, Micrograph of the terminal mycelial strand. Note the well-integrated fascicles of pigmented hyphae. The terminal hyphae are not aggregated and not pigmented. C, Micrograph of small squamules after squashing. Trebouxia-like algal cells are enveloped by mycobiont hyphae. Note autospores and a large pyrenoid in some of the algal cells. Scales: A grid in mm; B=45 ìm; C=18 ìm.
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Lichens growing on glass—Schroeter & Sancho
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F. 2. Details of lichens on glass. A, Mycelial strands with small squamules (arrowheads). B, Beaded and branched hyphae on glass. C, Ascospores in the gelatinous matrix between mycelial strands. D, Gelatinous connections attaching a hypha to the glass substratum. Scales: A=200 ìm; B=20 ìm; C=5 ìm; D=2 ìm.
at corroded surfaces, that is, areas damaged by chemical weathering (Brightman & Seaward 1978). We have occasionally detected several beaded hyphae (Fig. 2B), as reported by Bachmann (1904, 1917) for hypothalli. They strongly resemble the ascogonial filaments of the surface of a protoapothecium of a cultured mycobiont (Ahmadjian 1993). The dark mycelial net growing between small squamules also resembles the early stages of lichenization described by Asta et al. (1989) and Letrouit-Galinou & Asta (1994) in Rhizocarpon geographicum. In this case, areole formation was followed by a strong growth of dark peripheral hypothalline hyphae. However, in our samples, the young squamules appeared to develop upon the rhizomorphs and not vice versa (Fig. 2A). Recently, Sanders (1994) pointed out the potential significance of the rhizomorphic system in the vegetative spread of the lichen thallus. Rhizomorphs permit a more efficient colonization of substratum space and a more efficient exploitation of photobiont resources. In some instances, their presence may allow colonization of smooth faces of exfoliating crystalline rocks, very similar in texture to the artificial glass surfaces.
1996
Lichens growing on glass—Schroeter & Sancho
389
It seems more difficult to determine the age of the lichen colonization. The South Bay region, Livingston Island, is known for its comparatively mild climatic conditions favourable for lichen growth (Ban˜ón 1992; Sancho & Valladares 1993) and it is most probable that the pieces of broken glass were deposited at this location no more than 40 years ago. The pieces of clear glass we found to differ substantially from the broken bottles dating back to the 19th century sealing expeditions (1820s–1880s) to this area (Lewis Smith & Simpson 1987). When the Spanish Base was established in 1987, several uncovered rubbish dumps were found during the construction work in the vicinity and they were subsequently removed (J. Castellví Piulachs, pers. comm.). It is most probable that the colonized pieces of broken glass originate from one of these rubbish dumps. The pieces of glass were partly covered with pyroclasts, which probably originated from the 1970 volcanic eruption on Deception Island (see Baker & McReath 1971) that deposited volcanic material at South Bay, Livingston Island (J. M. Villaplana, pers. comm.). If this is true, it could be assumed that either the broken bottles were deposited after the 1970 volcanic eruption or, if deposited earlier, the glass surfaces were available for colonization only after the pyroclast cover had been removed by wind, rainfall, etc. Therefore it seems probable that colonization of the glass surfaces was initiated 22 years ago at the earliest and that it is not younger than 6 years. This would indicate that lichen colonization in the maritime Antarctic is not necessarily a slow process but, depending on the microclimatic situation, could proceed substantially within decades or even years. If compared with findings from other climatic regions (see Brightman & Seaward 1978) it is perhaps unsurprising that lichens are able to develop and grow on small pieces of broken glass in the maritime Antarctic, even though microclimatic conditions and water relations may differ from the natural habitat. Glass surfaces would have many advantages for microscopical investigations compared with rock surfaces. Colonization of glass surfaces by lichen propagules and ascospores could give easy access to the observation of the initial development and growth of the lichen thallus. Therefore, we propose the use of glass surfaces as a useful method if the establishment and growth of lichens are to be studied in extreme environments. The authors participated in several Spanish Antarctic expeditions to BAE Juan Carlos I. in Livingston Island. The members of these expeditions and in particular Prof. Dr J. Castellví Piulachs are thanked for their cooperation and hospitality (la mesa de los nin˜os) at BAE Juan Carlos I. Special thanks are directed to Dr C. Ascaso, Madrid, who gave technical support and access to the SEM, to Prof. Dr L. Kappen, Kiel, Dr W. Sanders, Madrid, and Dr R. I. Lewis Smith, Cambridge, for stimulating discussions, and to M. Sommerkorn, Kiel, for companionship in the field. The research was supported by the Deutsche Forschungsgemeinschaft (Ka 390/6-14) and by the Spanish GIGYT (ANT95–0405). R Ahmadjian, V. (1993) The Lichen Symbiosis. New York: John Wiley & Sons. Armstrong, R. A. (1975) Studies on the growth rates of lichens. In: Lichenology: Progress and Problems. (D. H. Brown, D. L. Hawksworth & R. H. Bailey, eds): 309–322. London: Academic Press. Asta, J., Letrouit, M. A. & Wagner, J. (1989) Colonisation de quartzites en milieu alpin par Rhizocarpon geographicum (L.) DC (Lichen crustacé saxicole). I. Les différents modes
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de développement du thalle. Traveaux Scientifiques du Parc Nacional de la Vanoise 17: 63–88. Bachmann, E. (1890) Die Beziehungen der Kalkflechten zu ihrem Substrat. Berichte der deutschen botanischen Gesellschaft 8: 143–145. Bachmann, E. (1904) Die Beziehungen der Kieselflechten zu ihrem Substrat. Berichte der deutschen botanischen Gesellschaft 22: 101–104. Bachmann, E. (1917) Die Beziehungen der Kieselflechten zu ihrer Unterlage. III. Bergkristall und Flint. Berichte der deutschen botanischen Gesselschaft 35: 464–476. Baker, P. E. & McReath I. (1971) 1970 volcanic eruption at Deception Island. Nature (Physical Science) 231: 5–9. Ban˜ón, M. (1992) El clima en las Shetland del Sur y el Norte de la Península Antártica. Caso de la B.A.E. ‘ Juan Carlos I. ’. Actas Simposio Espan˜ol de Estudios Antárticos 4: 25–39. Brightman, F. H. & Seaward, M. R. D. (1978) Lichens on man-made substrates. In: Lichen Ecology (M. R. D. Seaward, ed.): 253–293. London: Academic Press. Green, T. G. A. & Snelgar, W. P. (1977) Parmelia scabrosa growing on glass in New Zealand. Lichenologist 9: 170–172. Fahselt, D. & Sweet, S. (1991) Scanning electron microscopy of colonizing rock surfaces in the far north, Canada. Proceedings NIPR Symposium on Polar Biology 4: 107–113. Fahselt, D., Maycock, P. & Svoboda, J. (1988) Initial establishment of saxicolous lichens following recent glacial recession in Sverdrup Pass, Ellesmere Island, Canada. Lichenologist 20: 253–268. Kappen, L. (1993) Lichens in the Antarctic region. In Antarctic Microbiology. (E. I. Friedmann, ed.): 433–490. New York: Wiley-Liss. Letrouit-Galinou, M. A., Asta, J. (1994) Thallus morphogenesis in some lichens. Cryptogamic Botany 4: 274–282. Lewis Smith, R. I. & Simpson, H. W. (1987) Early nineteenth century sealers’ refuges on Livingston Island, South Shetland Islands. Bulletin British Antarctic Survey 74: 49–72. Malone, C. P. (1977) Observations on Endocarpon pusillum: on the role of rhizomorphs in asexual reproduction. Mycologia 69: 1042–1045. Mellor, E. (1923) Lichens and their action on the glass and leadings of church windows. Nature 112: 299–300. Ott, S. (1987a) Differences in the developmental rates of lichens. Annales Botanici Fennici 24: 385–393. Ott, S. (1987b) Sexual reproduction and developmental adaptations in Xanthoria parietina. Nordic Journal of Botany 7: 219–228. Sancho, L. G. & Valladares, F. (1993) Lichen colonization of recent moraines on Livingston Island (South Shetland I., Antarctica). Polar Biology 13: 227–233. Sanders, W. B. (1994) Role of lichen rhizinomorphs in thallus propagation and substrate colonization. Cryptogamic Botany 4: 283–289. Sanders, W. B. & Rico, V. J. (1992) Lichenizing rhizomorphs and thallus development in the squamulose lichen Aspicilia crespiana Rico ined. Botanica Acta 105: 449–456. Schroeter, B., Olech, M., Kappen, L. & Heitland, W. (1995) Ecophysiological investigations of Usnea antarctica in the maritime Antarctic. I. Annual microclimatic conditions and potential primary production. Antarctic Science 7: 251–260. Sipman, H. J. M. (1994) Foliicolous lichens on plastic tape. Lichenologist 26: 311–312. Valladares, F., Ascaso, C. & Sancho, L. G. (1994) Intrathalline variability of some structural and physical parameters in the lichen genus Lasallia. Canadian Journal of Botany 72: 415–428. Wagner, J. & Letrouit-Galinou, M. A. (1988) Structure et ontogenèse du thalle squamuleux du lichen Endocarpon pusillum. Canadian Journal of Botany 66: 2118–2127. Accepted for publication 17 December 1995
LICHENS GROWING ON GLASS IN ANTARCTICA B. SCHROETER* and L. G. SANCHO‡
Abstract: Early stages of lichen colonization on glass are reported for the first time from Antarctica. In the initial establishment of the lichen thallus rhizomorphs play an important role for the attachment to the substratum and the exploitation of nutrient and photobiont resources. The micrographs presented indicate that in Antarctica colonization of bare substrata by lichens is not necessarily an extremely slow process. Furthermore, our findings demonstrate that the use of artificial substrata such as glass could provide a simple method for studies in lichen colonization and development in extreme environments. ? 1996 The British Lichen Society
Introduction The lichen symbiosis is able to colonize a great variety of substrata. Besides natural substrata lichens grow also on man-made substrata derived from plant or animal sources such as cork, bones or leather (Brightman & Seaward 1978), synthetic material such as plastic tape (Sipman 1994), substrata derived from mineral sources such as bricks, cement, concrete roofs and walls, and glass and iron amongst others (Green & Snelgar 1977; Brightman & Seaward 1978). Vitricolous lichens can be of special interest because their smooth and often datable substratum may allow an accurate assessment of lichen growth rates (Armstrong 1975). Lichens growing on glass have been reported since the 19th century, predominantly from church windows in Europe (see Brightman & Seaward 1978), and several papers discuss a possible role of lichens in the deterioration of stained glass (see Mellor 1923). In favourable climates fast-growing species such as Parmelia scabrosa occur on glass surfaces of greenhouses and even on the windscreens of scrapped cars in New Zealand (Green & Snelgar 1977). In contrast, the extreme environmental conditions prevent comparable growth of lichens in Antarctica (see Kappen 1993; Schroeter et al. 1995). However, there is only a little information concerning the initial establishment and development of lichens in polar regions (Fahselt et al. 1988; Fahselt & Sweet 1991). Under Antarctic conditions, stability of the substratum seems to be one of the more important factors for lichen colonization. Therefore, it was unexpected to discover lichens growing on small pieces of broken glass on Livingston Island, maritime Antarctica, in January 1993. The small pieces of glass were partly covered with a network of hyphae and some small lichen areoles with algal cells, indicating early stages in the development of lichen thalli. *Botanisches Institut, Universität Kiel, Olshausenstraße 40, D-24098 Kiel, Federal Republic of Germany. ‡Departamento de Biologı´a Vegetal II, Facultad de Farmacia, Universidad Complutense, E-28040 Madrid, Spain. 0024–2829/96/040385+06 $18.00/0
? 1996 The British Lichen Society
386
THE LICHENOLOGIST
Vol. 28
Site Description and Methods Broken pieces of transparent glass were found in the vicinity of the Spanish Antarctic base BAE Juan Carlos I (62)40*S, 60)23*W) on Livingston Island, South Shetland Islands, maritime Antarctica, in January 1993. Broken glass of different sizes (from less than 0·5 cm2 up to 10 cm2) was distributed on the top of a boulder that was sparsely covered with Usnea antarctica and U. aurantiaco-atra. More pieces of broken glass were found on the ground nearby together with rusted tins, and partly covered by pyroclastic material. The pieces of glass originated from transparent bottles similar to Coca Cola bottles or bottles containing mineral water. Only a small part of the glass pieces showed signs of fungal/lichen colonization. Specimens were macroscopically and microscopically examined using a photomacroscope (Wild M400, FRG), a light microscope (Zeiss Jenaval, FRG) and a scanning electron microscope (Zeiss DSM-960, FRG) according to Valladares et al. (1994).
Results and Discussion Most of the early stages of colonization observed on the small pieces of glass were fungi and made up of dark-pigmented branched mycelial strands, occasionally developing young lichenized squamules (Figs 1A & 2A). The squamules always contained several algal cells (Trebouxia type) enveloped by mycobiont hyphae (Fig. 1C). The presence of lichenized algae clearly indicates that the samples represent initial stages in the development of a lichen. The hyphae probably started from ascospores, which were relatively frequent between them (Fig. 2C), whereas vegetative diaspores were not present. It is known that the development of new thalli can be as rapid from vegetative diaspores as from ascospores (Ott 1987a,b). The mycelial strands were multihyphal linear aggregates, the terminal cells of which were quite elongated and not pigmented (Fig. 1B), probably indicating apical extension. This concurs very well with the concept that lichen rhizomorphs are a form of specialized hypothallus (Malone 1977; Wagner & Letrouit-Galinou 1988; Sanders & Rico 1992; Sanders 1994). Furthermore, as in the case of typical rhizomorphs (first described by Bachmann 1890), the mycelial strands growing on the Antarctic glass are well-integrated fascicles of hyphae in a common intercellular gelatinous matrix, rather than a loose association of hyphae (Fig. 2B). In lichens a gelatinous matrix not only facilitates early physical contacts between the bionts and glues hyphae into compact layers (Ahmadjian 1993) but also permits attachment to the substratum, as was observed in some cases (Fig. 2D). Colonization of the substratum always started in areas with a deteriorated surface, that is, with cracks and fissures that result from the break up of the glass bottles. A damaged surface seems to allow a much better attachment of the hyphae to the substratum. This was also true for the colonization of church windows where lichens were found only F. 1. Lichens on glass. A, Early stages of lichen colonization of glass. Mycelial strands growing on a small piece of glass. The dark-pigmented fungal branches are preferentially attached to small fissures in the glass but also extend over smooth areas. B, Micrograph of the terminal mycelial strand. Note the well-integrated fascicles of pigmented hyphae. The terminal hyphae are not aggregated and not pigmented. C, Micrograph of small squamules after squashing. Trebouxia-like algal cells are enveloped by mycobiont hyphae. Note autospores and a large pyrenoid in some of the algal cells. Scales: A grid in mm; B=45 ìm; C=18 ìm.
1996
Lichens growing on glass—Schroeter & Sancho
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THE LICHENOLOGIST
Vol. 28
F. 2. Details of lichens on glass. A, Mycelial strands with small squamules (arrowheads). B, Beaded and branched hyphae on glass. C, Ascospores in the gelatinous matrix between mycelial strands. D, Gelatinous connections attaching a hypha to the glass substratum. Scales: A=200 ìm; B=20 ìm; C=5 ìm; D=2 ìm.
at corroded surfaces, that is, areas damaged by chemical weathering (Brightman & Seaward 1978). We have occasionally detected several beaded hyphae (Fig. 2B), as reported by Bachmann (1904, 1917) for hypothalli. They strongly resemble the ascogonial filaments of the surface of a protoapothecium of a cultured mycobiont (Ahmadjian 1993). The dark mycelial net growing between small squamules also resembles the early stages of lichenization described by Asta et al. (1989) and Letrouit-Galinou & Asta (1994) in Rhizocarpon geographicum. In this case, areole formation was followed by a strong growth of dark peripheral hypothalline hyphae. However, in our samples, the young squamules appeared to develop upon the rhizomorphs and not vice versa (Fig. 2A). Recently, Sanders (1994) pointed out the potential significance of the rhizomorphic system in the vegetative spread of the lichen thallus. Rhizomorphs permit a more efficient colonization of substratum space and a more efficient exploitation of photobiont resources. In some instances, their presence may allow colonization of smooth faces of exfoliating crystalline rocks, very similar in texture to the artificial glass surfaces.
1996
Lichens growing on glass—Schroeter & Sancho
389
It seems more difficult to determine the age of the lichen colonization. The South Bay region, Livingston Island, is known for its comparatively mild climatic conditions favourable for lichen growth (Ban˜ón 1992; Sancho & Valladares 1993) and it is most probable that the pieces of broken glass were deposited at this location no more than 40 years ago. The pieces of clear glass we found to differ substantially from the broken bottles dating back to the 19th century sealing expeditions (1820s–1880s) to this area (Lewis Smith & Simpson 1987). When the Spanish Base was established in 1987, several uncovered rubbish dumps were found during the construction work in the vicinity and they were subsequently removed (J. Castellví Piulachs, pers. comm.). It is most probable that the colonized pieces of broken glass originate from one of these rubbish dumps. The pieces of glass were partly covered with pyroclasts, which probably originated from the 1970 volcanic eruption on Deception Island (see Baker & McReath 1971) that deposited volcanic material at South Bay, Livingston Island (J. M. Villaplana, pers. comm.). If this is true, it could be assumed that either the broken bottles were deposited after the 1970 volcanic eruption or, if deposited earlier, the glass surfaces were available for colonization only after the pyroclast cover had been removed by wind, rainfall, etc. Therefore it seems probable that colonization of the glass surfaces was initiated 22 years ago at the earliest and that it is not younger than 6 years. This would indicate that lichen colonization in the maritime Antarctic is not necessarily a slow process but, depending on the microclimatic situation, could proceed substantially within decades or even years. If compared with findings from other climatic regions (see Brightman & Seaward 1978) it is perhaps unsurprising that lichens are able to develop and grow on small pieces of broken glass in the maritime Antarctic, even though microclimatic conditions and water relations may differ from the natural habitat. Glass surfaces would have many advantages for microscopical investigations compared with rock surfaces. Colonization of glass surfaces by lichen propagules and ascospores could give easy access to the observation of the initial development and growth of the lichen thallus. Therefore, we propose the use of glass surfaces as a useful method if the establishment and growth of lichens are to be studied in extreme environments. The authors participated in several Spanish Antarctic expeditions to BAE Juan Carlos I. in Livingston Island. The members of these expeditions and in particular Prof. Dr J. Castellví Piulachs are thanked for their cooperation and hospitality (la mesa de los nin˜os) at BAE Juan Carlos I. Special thanks are directed to Dr C. Ascaso, Madrid, who gave technical support and access to the SEM, to Prof. Dr L. Kappen, Kiel, Dr W. Sanders, Madrid, and Dr R. I. Lewis Smith, Cambridge, for stimulating discussions, and to M. Sommerkorn, Kiel, for companionship in the field. The research was supported by the Deutsche Forschungsgemeinschaft (Ka 390/6-14) and by the Spanish GIGYT (ANT95–0405). R Ahmadjian, V. (1993) The Lichen Symbiosis. New York: John Wiley & Sons. Armstrong, R. A. (1975) Studies on the growth rates of lichens. In: Lichenology: Progress and Problems. (D. H. Brown, D. L. Hawksworth & R. H. Bailey, eds): 309–322. London: Academic Press. Asta, J., Letrouit, M. A. & Wagner, J. (1989) Colonisation de quartzites en milieu alpin par Rhizocarpon geographicum (L.) DC (Lichen crustacé saxicole). I. Les différents modes
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de développement du thalle. Traveaux Scientifiques du Parc Nacional de la Vanoise 17: 63–88. Bachmann, E. (1890) Die Beziehungen der Kalkflechten zu ihrem Substrat. Berichte der deutschen botanischen Gesellschaft 8: 143–145. Bachmann, E. (1904) Die Beziehungen der Kieselflechten zu ihrem Substrat. Berichte der deutschen botanischen Gesellschaft 22: 101–104. Bachmann, E. (1917) Die Beziehungen der Kieselflechten zu ihrer Unterlage. III. Bergkristall und Flint. Berichte der deutschen botanischen Gesselschaft 35: 464–476. Baker, P. E. & McReath I. (1971) 1970 volcanic eruption at Deception Island. Nature (Physical Science) 231: 5–9. Ban˜ón, M. (1992) El clima en las Shetland del Sur y el Norte de la Península Antártica. Caso de la B.A.E. ‘ Juan Carlos I. ’. Actas Simposio Espan˜ol de Estudios Antárticos 4: 25–39. Brightman, F. H. & Seaward, M. R. D. (1978) Lichens on man-made substrates. In: Lichen Ecology (M. R. D. Seaward, ed.): 253–293. London: Academic Press. Green, T. G. A. & Snelgar, W. P. (1977) Parmelia scabrosa growing on glass in New Zealand. Lichenologist 9: 170–172. Fahselt, D. & Sweet, S. (1991) Scanning electron microscopy of colonizing rock surfaces in the far north, Canada. Proceedings NIPR Symposium on Polar Biology 4: 107–113. Fahselt, D., Maycock, P. & Svoboda, J. (1988) Initial establishment of saxicolous lichens following recent glacial recession in Sverdrup Pass, Ellesmere Island, Canada. Lichenologist 20: 253–268. Kappen, L. (1993) Lichens in the Antarctic region. In Antarctic Microbiology. (E. I. Friedmann, ed.): 433–490. New York: Wiley-Liss. Letrouit-Galinou, M. A., Asta, J. (1994) Thallus morphogenesis in some lichens. Cryptogamic Botany 4: 274–282. Lewis Smith, R. I. & Simpson, H. W. (1987) Early nineteenth century sealers’ refuges on Livingston Island, South Shetland Islands. Bulletin British Antarctic Survey 74: 49–72. Malone, C. P. (1977) Observations on Endocarpon pusillum: on the role of rhizomorphs in asexual reproduction. Mycologia 69: 1042–1045. Mellor, E. (1923) Lichens and their action on the glass and leadings of church windows. Nature 112: 299–300. Ott, S. (1987a) Differences in the developmental rates of lichens. Annales Botanici Fennici 24: 385–393. Ott, S. (1987b) Sexual reproduction and developmental adaptations in Xanthoria parietina. Nordic Journal of Botany 7: 219–228. Sancho, L. G. & Valladares, F. (1993) Lichen colonization of recent moraines on Livingston Island (South Shetland I., Antarctica). Polar Biology 13: 227–233. Sanders, W. B. (1994) Role of lichen rhizinomorphs in thallus propagation and substrate colonization. Cryptogamic Botany 4: 283–289. Sanders, W. B. & Rico, V. J. (1992) Lichenizing rhizomorphs and thallus development in the squamulose lichen Aspicilia crespiana Rico ined. Botanica Acta 105: 449–456. Schroeter, B., Olech, M., Kappen, L. & Heitland, W. (1995) Ecophysiological investigations of Usnea antarctica in the maritime Antarctic. I. Annual microclimatic conditions and potential primary production. Antarctic Science 7: 251–260. Sipman, H. J. M. (1994) Foliicolous lichens on plastic tape. Lichenologist 26: 311–312. Valladares, F., Ascaso, C. & Sancho, L. G. (1994) Intrathalline variability of some structural and physical parameters in the lichen genus Lasallia. Canadian Journal of Botany 72: 415–428. Wagner, J. & Letrouit-Galinou, M. A. (1988) Structure et ontogenèse du thalle squamuleux du lichen Endocarpon pusillum. Canadian Journal of Botany 66: 2118–2127. Accepted for publication 17 December 1995