- Email: [email protected]
Natural CO2 springs: obstacle or opportunity?
BOOK REVIEWS 42 Ives, A.R. and Settle, W.H. (1997) Metapopulation dynamics and pest control in agricultural systems, Am. Nat. 149, 220–246 43 Settle, W.H. et al. (1996) Managing tropical rice pests through conservation of generalist natural enemies and alternative prey, Ecology 77, 1975–1988 44 Khan, Z.R. et al. (1997) Intercropping increases parasitism of pests, Nature 388, 631–632
Designer snails The Algorithmic Beauty of Sea Shells (2nd edn) by Hans Meinhardt Springer-Verlag, 1998. DM89.00/$54.95/£34.00 hbk (xi + 236 pages) ISBN 3 540 63919 5
M
ollusc shells, especially those from the marine tropics, often display complex and beautiful color patterns. Multicolored bands, oblique sets of lines, chevrons, dots, triangles and combinations of these are superimposed on the regularly coiled shells of gastropods, bivalves and the pearly nautilus. In burrowing species, at least, the adaptive value of shell pigmentation is puzzling because the patterns are never seen in life by other members of the same or other species. Perhaps because of this, intraspecific variation in color pattern tends to be high even though basic themes are repeated over and over within and among species. Many biologists and mathematicians have attempted to make sense of these bizarre patterns, starting with Waddington and Coe in 1969 (Ref.1) and including Wolfram’s models based on cellular automata2. But Hans Meinhardt has done by far the most extensive research and has probably come closest to an explanatory model. Because very little is actually known about the physiological mechanisms of the pattern formation, Meinhardt uses computer simulations to test ad hoc models against the variety of actual patterns in nature. This is a dangerous strategy, of course, but the results are truly impressive. Using a fairly simple model based on the nonlinear dynamics of pigment production and inhibition, plus diffusion to neighboring sites, Meinhardt has successfully simulated virtually the entire range of molluscan color patterns. These are documented by scores of color photographs of actual shells with matching simulations. The result is not only convincing but also makes a beautiful volume. The success of Meinhardt’s model is such that the real world must use something close to this algorithm. TREE vol. 13, no. 9 September 1998
45 Getz, W.M. and Haight, R.G. (1989) Population Harvesting: Demographic Models of Fish, Forest and Animal Resources, Princeton University Press 46 Roland, J. and Taylor, P.D. (1997) Insect species respond to forest structure at different spatial scales, Nature 386, 710–713 47 Shackell, N.L. and Willison, J.H.M. (1995) Marine Protected Areas and Sustainable Fisheries, Science and Management of Protected Areas Association
48 Brown, G. and Roughgarden, J. (1997) A metapopulation model with private property and a common pool, Ecol. Econ. 22, 65–71 49 Orensanz, J.M. and Jamieson, G. The assessment and management of spatially structured stocks, in North Pacific Symposium on Invertebrate Stock Assessment and Management 1995 (Jamieson, G. and Campbell, A., eds), Canadian Special Publication in Fisheries and Aquatic Sciences (Vol. 125) (in press)
A disk is provided containing a DOSexecutable program whereby one can reproduce the simulations illustrated in the book or explore other possibilities within the parameter space defined by the basic equations. The program is easy to use and the disk includes the full source code so the user can read, trouble-shoot or change the algorithm. Meinhardt’s simulations are shown as two-dimensional plan views, appropriate to his mission because it avoids the distortion of the pattern being superimposed on the curved, spiral surface of the shell. However, a special chapter by Prusinkiewicz and Fowler adds the third dimension. The color pattern algorithm is combined with earlier work on computer representation of spiral shell forms3 to produce a series of truly remarkable graphics. Photographs of real shells are shown alongside simulations. The shell geometries and color patterns are matched so perfectly that it is often hard to tell which is which. This is not only scientifically important, but also further adds to the beauty of the book. Throughout The Algorithmic Beauty of Sea Shells, Meinhardt emphasizes that he is using color patterns in shells only as a vehicle to learn about a host of other developmental systems in which oscillations, traveling waves and similar phenomena are common. The great advantage of using shells is that the pigmentation generally occurs during accretionary growth of the shell, so that the adult shell carries a complete historical record of the process. With the time dimension preserved, validation of the model is far more rigorous than if the time sequence had to be inferred. In the final chapter, curiously titled as an appendix, Meinhardt explores the potential applications of his activator– inhibitor model to a wide variety of problems posed by development in other animal and plant groups. At the very least, this should provide a valuable source of hunches for people working with problems as far afield as limb buds in vertebrates and vein patterns in leaves.
References
David M. Raup University of Chicago, RR1 Box 168-Y, Washington Island, WI 54246, USA ([email protected])
1 Waddington, C. and Coe, R. (1969) J. Theor. Biol. 25, 219–225 2 Wolfram, S. (1984) Nature 341, 419–424 3 Fowler, D.R., Meinhardt, H. and Prusinkiewicz, P. (1992) Comput. Graph. 26, 379–387
Natural CO2 springs: obstacle or opportunity? Plant Responses to Elevated Carbon Dioxide: Evidence from Natural Springs edited by A. Raschi, F. Miglietta, R. Tognetti and P.R. van Gardingen Cambridge University Press, 1997. £40.00/$69.95 hbk (xiv + 272 pages) ISBN 0 521 58203 2
A
side from its influence on the climate system, the increasing concentration of atmospheric CO2 has direct effects on plants and ecosystems via photosynthesis1–3. Since the middle of the 1980s, there has been a flood of research designed to evaluate and predict such direct CO2 effects. Recently, however, strong concerns have been expressed as to whether we can sufficiently predict plant and ecosystem responses to rising CO2 levels purely from experiments of short-term, ambient versus double-ambient CO2 concentrations, which have predominated in the field4–6. Natural CO2 Springs is the product of a workshop on ‘Carbon Dioxide Springs and Their Use in Biological Research’ in 1993. It provides an excellent overview of ongoing and planned research at sites near naturally occurring CO2 springs from Iceland to central Africa but with a focus on Italy. In the field of CO2 research, debate still rages about the scientific value of ecological experiments conducted using this natural form of atmospheric CO2 enrichment. Indeed, the debate permeates the entire book, with nearly all of the 18 chapters comprehensively but repetitively discussing the advantages and disadvantages of using CO2 springs.
Copyright © 1998, Elsevier Science Ltd. All rights reserved. 0169-5347/98/$19.00
375
BOOK REVIEWS The advantages seem striking. For the first time we have the opportunity to study processes at the community and ecosystem scales within intact ecosystems that have evolved under elevated CO2 levels over centuries and have therefore been exposed to truly long-term ‘CO2 enrichment’. The authors almost unanimously emphasize both the system-level approach and the fact that the extraordinarily long period of CO2 exposure has allowed phenotypic and genetic adaptations that are both major advantages of CO2 springs. However, a clear concern of the authors is the difficulty of finding adequate control sites, with questions raised about the comparability of microclimate, soil, species composition and management history. Natural CO2 Springs is not biased towards one particular approach, such as designed experiments or the use of natural CO2 springs, and therefore contributes greatly towards our understanding of the limitations and advantages of different techniques. Consequently, the authors provide us with the insight that we need to use many different experimental approaches to be able to optimize our knowledge of how native plants and natural ecosystems respond to increasing concentrations of atmospheric CO2. The book also provides thoughtful ideas about how to use CO2 springs in ways other than simply comparing the spring with the control areas: (1) studying vegetational responses to varying CO2 concentrations along transects extending from the outside to the center of the springs; (2) comparing plant responses across biomes at several CO2 springs; (3) using plants taken from the springs for detailed studies on ‘adapted’ material; and (4) using the CO2 emitted from the springs for replicated experiments. It is the discussion about the possibilities and difficulties of working at various CO2 springs, rather than exciting new results, that makes this book attractive. Only about half the chapters include some experimental data and many of these are preliminary in character. These experiments, however, are among the first of their kind to be initiated and consequently serve as a basis for future research. An important question is how well these first results agree with those obtained from much shorter-term CO2 enrichment studies conducted under more artificial conditions? The answer to this question is likely to influence our thoughts about CO2 spring research more than we care to admit. Well, there is ‘good news’ from the springs. Several results obtained at the CO2 springs confirm those found in previous experimental efforts. Among these are not only initial growth stimulation and increased leaf-level photosynthesis, but also downward adjustments of photosynthesis, plant tissue quality changes, changes in short-term decomposition rates and, perhaps most importantly, confirmation that not all species respond to CO2 enrich-
376
ment in the same way. Other apparently conflicting results, such as declining growth responses, might indeed result from differences between intact ecosystems and artificial experimental arrangements, or how we interpret the results from the latter. The main message of this book is that natural CO2 springs provide another valid and useful means to study responses of plants, communities and ecosystems to elevated CO2 levels, and are a great opportunity to gain further insights into what can occur as atmospheric CO2 levels continue to increase. I recommend this book to everyone working in this field.
Stephan Hättenschwiler Dept of Integrative Biology, University of Basel, Schönbeinstrasse 6, CH-4056 Basel, Switzerland ([email protected])
References 1 Amthor, J.S. (1995) Glob. Change Biol. 1, 243–274 2 Bazzaz, F.A. (1990) Annu. Rev. Ecol. Syst. 21, 167–196 3 Mooney, H.A. et al. (1991) BioScience 41, 96–104 4 Ackerly, D.D. and Bazzaz, F.A. (1995) Glob. Change Biol. 1, 199–207 5 Körner, C. (1995) Plant Cell. Environ. 18, 1101–1110 6 Loehle, C. (1995) Oikos 73, 181–187
Receding black moths Melanism: Evolution in Action by Michael E.N. Majerus Oxford University Press, 1998. £55.00/$105.00 hbk, £23.95/$45.00 pbk (xiii + 352 pages) ISBN 0 19 854983 0 / 0 19 854 982 2
A
lthough industrial melanism largely retains its grip on a place in evolution textbooks, it now receives little attention from active scientists. I welcomed the arrival of this book hoping that it would reinvigorate our community. The peppered moth, Biston betularia, is rightly regarded as a striking example of adaptive change through natural selection and as one of the foundation stones for the modern synthesis of evolutionary theory. What do we learn from Majerus’s book that we could not glean from Kettlewell’s treatise published 25 years ago1, and how effective will it be in stimulating further research? The central force of this book and indeed of melanism as an evolutionary paradigm comes in the two pivotal chapters devoted to the peppered moth. I particularly enjoyed the description of Kettlewell’s classic experiments. Majerus contrasts the straightforward textbook accounts of industrial melanism with the complexity of what we actually know
Copyright © 1998, Elsevier Science Ltd. All rights reserved. 0169-5347/98/$19.00
about selection and allele changes at the carbonaria gene in natural populations. The one unequivocally new and fascinating element in the story is the present-day declines in melanic frequency. These are covered well in Majerus’s book, although I find it odd that there is no reference to work on the ebony gene in Drosophila melanogaster, where much is known about molecular mechanisms and where there is a clear effect of the gene on adult activity and mating behaviour2. I find the idea of manifold effects of the carbonaria gene on fitness, some via effects on crypsis and others through nonvisual effects, rather persuasive. Majerus and his co-workers have concentrated more on resting site selection by the morphs, although it remains notoriously difficult to quantify such effects in a way that can be convincingly related to moth behaviour in nature. The earlier part of the book includes a general introduction to melanism and covers some basic principles of evolutionary genetics. Although the author is writing for amateur entomologists as well as academics, I am not sure that these chapters are worth the space. Later on, there is a curiously inappropriate section on mimicry and a description of melanism in ladybird beetles (Coccinellidae). The latter work illustrates that unitary explanations for melanic polymorphisms are unlikely to be found. Majerus’s own work on female preference in two-spot ladybirds rests rather uneasily alongside research on thermal melanism and aposematism. Also, the wide-ranging research on the potential of melanization of the cuticle or skin to influence thermal budgets and population biology is not well represented. As Majerus notes, the glaring omission in work on melanism is any molecular approach. The gap between the alleles at the carbonaria gene and the phenotypes on which selection has been demonstrated to act so convincingly remains a void in terms of any mechanistic understanding. In view of the power of molecular tools and the understanding of the biochemistry of melanization, this seems almost to amount to criminal negligence. It is striking that this still applies to all the classic examples of adaptive traits that were so beloved by the E.B. Ford school of ecological geneticists3.
Paul M. Brakefield Institute of Evolutionary and Ecological Sciences, Leiden University, PO Box 9516, 2300 RA Leiden, The Netherlands ([email protected])
References 1 Kettlewell, H.B.D. (1973) The Evolution of Melanism, Clarendon Press 2 Kyriacou, C.P., Burnett, B. and Connolly, K. (1978) Anim. Behav. 26, 1195–1206 3 Ford, E.B. (1975) Ecological Genetics, Chapman & Hall TREE vol. 13, no. 9 September 1998
Designer snails The Algorithmic Beauty of Sea Shells (2nd edn) by Hans Meinhardt Springer-Verlag, 1998. DM89.00/$54.95/£34.00 hbk (xi + 236 pages) ISBN 3 540 63919 5
M
ollusc shells, especially those from the marine tropics, often display complex and beautiful color patterns. Multicolored bands, oblique sets of lines, chevrons, dots, triangles and combinations of these are superimposed on the regularly coiled shells of gastropods, bivalves and the pearly nautilus. In burrowing species, at least, the adaptive value of shell pigmentation is puzzling because the patterns are never seen in life by other members of the same or other species. Perhaps because of this, intraspecific variation in color pattern tends to be high even though basic themes are repeated over and over within and among species. Many biologists and mathematicians have attempted to make sense of these bizarre patterns, starting with Waddington and Coe in 1969 (Ref.1) and including Wolfram’s models based on cellular automata2. But Hans Meinhardt has done by far the most extensive research and has probably come closest to an explanatory model. Because very little is actually known about the physiological mechanisms of the pattern formation, Meinhardt uses computer simulations to test ad hoc models against the variety of actual patterns in nature. This is a dangerous strategy, of course, but the results are truly impressive. Using a fairly simple model based on the nonlinear dynamics of pigment production and inhibition, plus diffusion to neighboring sites, Meinhardt has successfully simulated virtually the entire range of molluscan color patterns. These are documented by scores of color photographs of actual shells with matching simulations. The result is not only convincing but also makes a beautiful volume. The success of Meinhardt’s model is such that the real world must use something close to this algorithm. TREE vol. 13, no. 9 September 1998
45 Getz, W.M. and Haight, R.G. (1989) Population Harvesting: Demographic Models of Fish, Forest and Animal Resources, Princeton University Press 46 Roland, J. and Taylor, P.D. (1997) Insect species respond to forest structure at different spatial scales, Nature 386, 710–713 47 Shackell, N.L. and Willison, J.H.M. (1995) Marine Protected Areas and Sustainable Fisheries, Science and Management of Protected Areas Association
48 Brown, G. and Roughgarden, J. (1997) A metapopulation model with private property and a common pool, Ecol. Econ. 22, 65–71 49 Orensanz, J.M. and Jamieson, G. The assessment and management of spatially structured stocks, in North Pacific Symposium on Invertebrate Stock Assessment and Management 1995 (Jamieson, G. and Campbell, A., eds), Canadian Special Publication in Fisheries and Aquatic Sciences (Vol. 125) (in press)
A disk is provided containing a DOSexecutable program whereby one can reproduce the simulations illustrated in the book or explore other possibilities within the parameter space defined by the basic equations. The program is easy to use and the disk includes the full source code so the user can read, trouble-shoot or change the algorithm. Meinhardt’s simulations are shown as two-dimensional plan views, appropriate to his mission because it avoids the distortion of the pattern being superimposed on the curved, spiral surface of the shell. However, a special chapter by Prusinkiewicz and Fowler adds the third dimension. The color pattern algorithm is combined with earlier work on computer representation of spiral shell forms3 to produce a series of truly remarkable graphics. Photographs of real shells are shown alongside simulations. The shell geometries and color patterns are matched so perfectly that it is often hard to tell which is which. This is not only scientifically important, but also further adds to the beauty of the book. Throughout The Algorithmic Beauty of Sea Shells, Meinhardt emphasizes that he is using color patterns in shells only as a vehicle to learn about a host of other developmental systems in which oscillations, traveling waves and similar phenomena are common. The great advantage of using shells is that the pigmentation generally occurs during accretionary growth of the shell, so that the adult shell carries a complete historical record of the process. With the time dimension preserved, validation of the model is far more rigorous than if the time sequence had to be inferred. In the final chapter, curiously titled as an appendix, Meinhardt explores the potential applications of his activator– inhibitor model to a wide variety of problems posed by development in other animal and plant groups. At the very least, this should provide a valuable source of hunches for people working with problems as far afield as limb buds in vertebrates and vein patterns in leaves.
References
David M. Raup University of Chicago, RR1 Box 168-Y, Washington Island, WI 54246, USA ([email protected])
1 Waddington, C. and Coe, R. (1969) J. Theor. Biol. 25, 219–225 2 Wolfram, S. (1984) Nature 341, 419–424 3 Fowler, D.R., Meinhardt, H. and Prusinkiewicz, P. (1992) Comput. Graph. 26, 379–387
Natural CO2 springs: obstacle or opportunity? Plant Responses to Elevated Carbon Dioxide: Evidence from Natural Springs edited by A. Raschi, F. Miglietta, R. Tognetti and P.R. van Gardingen Cambridge University Press, 1997. £40.00/$69.95 hbk (xiv + 272 pages) ISBN 0 521 58203 2
A
side from its influence on the climate system, the increasing concentration of atmospheric CO2 has direct effects on plants and ecosystems via photosynthesis1–3. Since the middle of the 1980s, there has been a flood of research designed to evaluate and predict such direct CO2 effects. Recently, however, strong concerns have been expressed as to whether we can sufficiently predict plant and ecosystem responses to rising CO2 levels purely from experiments of short-term, ambient versus double-ambient CO2 concentrations, which have predominated in the field4–6. Natural CO2 Springs is the product of a workshop on ‘Carbon Dioxide Springs and Their Use in Biological Research’ in 1993. It provides an excellent overview of ongoing and planned research at sites near naturally occurring CO2 springs from Iceland to central Africa but with a focus on Italy. In the field of CO2 research, debate still rages about the scientific value of ecological experiments conducted using this natural form of atmospheric CO2 enrichment. Indeed, the debate permeates the entire book, with nearly all of the 18 chapters comprehensively but repetitively discussing the advantages and disadvantages of using CO2 springs.
Copyright © 1998, Elsevier Science Ltd. All rights reserved. 0169-5347/98/$19.00
375
BOOK REVIEWS The advantages seem striking. For the first time we have the opportunity to study processes at the community and ecosystem scales within intact ecosystems that have evolved under elevated CO2 levels over centuries and have therefore been exposed to truly long-term ‘CO2 enrichment’. The authors almost unanimously emphasize both the system-level approach and the fact that the extraordinarily long period of CO2 exposure has allowed phenotypic and genetic adaptations that are both major advantages of CO2 springs. However, a clear concern of the authors is the difficulty of finding adequate control sites, with questions raised about the comparability of microclimate, soil, species composition and management history. Natural CO2 Springs is not biased towards one particular approach, such as designed experiments or the use of natural CO2 springs, and therefore contributes greatly towards our understanding of the limitations and advantages of different techniques. Consequently, the authors provide us with the insight that we need to use many different experimental approaches to be able to optimize our knowledge of how native plants and natural ecosystems respond to increasing concentrations of atmospheric CO2. The book also provides thoughtful ideas about how to use CO2 springs in ways other than simply comparing the spring with the control areas: (1) studying vegetational responses to varying CO2 concentrations along transects extending from the outside to the center of the springs; (2) comparing plant responses across biomes at several CO2 springs; (3) using plants taken from the springs for detailed studies on ‘adapted’ material; and (4) using the CO2 emitted from the springs for replicated experiments. It is the discussion about the possibilities and difficulties of working at various CO2 springs, rather than exciting new results, that makes this book attractive. Only about half the chapters include some experimental data and many of these are preliminary in character. These experiments, however, are among the first of their kind to be initiated and consequently serve as a basis for future research. An important question is how well these first results agree with those obtained from much shorter-term CO2 enrichment studies conducted under more artificial conditions? The answer to this question is likely to influence our thoughts about CO2 spring research more than we care to admit. Well, there is ‘good news’ from the springs. Several results obtained at the CO2 springs confirm those found in previous experimental efforts. Among these are not only initial growth stimulation and increased leaf-level photosynthesis, but also downward adjustments of photosynthesis, plant tissue quality changes, changes in short-term decomposition rates and, perhaps most importantly, confirmation that not all species respond to CO2 enrich-
376
ment in the same way. Other apparently conflicting results, such as declining growth responses, might indeed result from differences between intact ecosystems and artificial experimental arrangements, or how we interpret the results from the latter. The main message of this book is that natural CO2 springs provide another valid and useful means to study responses of plants, communities and ecosystems to elevated CO2 levels, and are a great opportunity to gain further insights into what can occur as atmospheric CO2 levels continue to increase. I recommend this book to everyone working in this field.
Stephan Hättenschwiler Dept of Integrative Biology, University of Basel, Schönbeinstrasse 6, CH-4056 Basel, Switzerland ([email protected])
References 1 Amthor, J.S. (1995) Glob. Change Biol. 1, 243–274 2 Bazzaz, F.A. (1990) Annu. Rev. Ecol. Syst. 21, 167–196 3 Mooney, H.A. et al. (1991) BioScience 41, 96–104 4 Ackerly, D.D. and Bazzaz, F.A. (1995) Glob. Change Biol. 1, 199–207 5 Körner, C. (1995) Plant Cell. Environ. 18, 1101–1110 6 Loehle, C. (1995) Oikos 73, 181–187
Receding black moths Melanism: Evolution in Action by Michael E.N. Majerus Oxford University Press, 1998. £55.00/$105.00 hbk, £23.95/$45.00 pbk (xiii + 352 pages) ISBN 0 19 854983 0 / 0 19 854 982 2
A
lthough industrial melanism largely retains its grip on a place in evolution textbooks, it now receives little attention from active scientists. I welcomed the arrival of this book hoping that it would reinvigorate our community. The peppered moth, Biston betularia, is rightly regarded as a striking example of adaptive change through natural selection and as one of the foundation stones for the modern synthesis of evolutionary theory. What do we learn from Majerus’s book that we could not glean from Kettlewell’s treatise published 25 years ago1, and how effective will it be in stimulating further research? The central force of this book and indeed of melanism as an evolutionary paradigm comes in the two pivotal chapters devoted to the peppered moth. I particularly enjoyed the description of Kettlewell’s classic experiments. Majerus contrasts the straightforward textbook accounts of industrial melanism with the complexity of what we actually know
Copyright © 1998, Elsevier Science Ltd. All rights reserved. 0169-5347/98/$19.00
about selection and allele changes at the carbonaria gene in natural populations. The one unequivocally new and fascinating element in the story is the present-day declines in melanic frequency. These are covered well in Majerus’s book, although I find it odd that there is no reference to work on the ebony gene in Drosophila melanogaster, where much is known about molecular mechanisms and where there is a clear effect of the gene on adult activity and mating behaviour2. I find the idea of manifold effects of the carbonaria gene on fitness, some via effects on crypsis and others through nonvisual effects, rather persuasive. Majerus and his co-workers have concentrated more on resting site selection by the morphs, although it remains notoriously difficult to quantify such effects in a way that can be convincingly related to moth behaviour in nature. The earlier part of the book includes a general introduction to melanism and covers some basic principles of evolutionary genetics. Although the author is writing for amateur entomologists as well as academics, I am not sure that these chapters are worth the space. Later on, there is a curiously inappropriate section on mimicry and a description of melanism in ladybird beetles (Coccinellidae). The latter work illustrates that unitary explanations for melanic polymorphisms are unlikely to be found. Majerus’s own work on female preference in two-spot ladybirds rests rather uneasily alongside research on thermal melanism and aposematism. Also, the wide-ranging research on the potential of melanization of the cuticle or skin to influence thermal budgets and population biology is not well represented. As Majerus notes, the glaring omission in work on melanism is any molecular approach. The gap between the alleles at the carbonaria gene and the phenotypes on which selection has been demonstrated to act so convincingly remains a void in terms of any mechanistic understanding. In view of the power of molecular tools and the understanding of the biochemistry of melanization, this seems almost to amount to criminal negligence. It is striking that this still applies to all the classic examples of adaptive traits that were so beloved by the E.B. Ford school of ecological geneticists3.
Paul M. Brakefield Institute of Evolutionary and Ecological Sciences, Leiden University, PO Box 9516, 2300 RA Leiden, The Netherlands ([email protected])
References 1 Kettlewell, H.B.D. (1973) The Evolution of Melanism, Clarendon Press 2 Kyriacou, C.P., Burnett, B. and Connolly, K. (1978) Anim. Behav. 26, 1195–1206 3 Ford, E.B. (1975) Ecological Genetics, Chapman & Hall TREE vol. 13, no. 9 September 1998