PHYTOLITH LITERATURE REVIEW

Attached is a brief intro to Phytoliths taken form the following publication:

Ball, T.B., and J. D. Brotherson. 1992.

The effect of varying environmental conditions on phytolith morphology in two species of grass (Bouteloua curtipendula and Panicum virgatum). Scanning Electron Microscopy 6:1163-1182.

Other more recent publications in which I discuss similar topics include:

Ball, T.B., J.D. Brotherson, and J.S. Gardner. 1996.

Identifying phytoliths produced by the inflorescence bracts of three species of wheat (Triticum monoccocum L., T. dicoccon Schrank., and T. aestivum L.) using computer-assisted image and statistical analyses. Journal of Archaeological Science 23:619-632.

and

Ball, T.B., J.D. Brotherson, and J.S. Gardner. 1993.

A typologic and morphometric study of phytoliths from einkorn wheat (Triticum monococcum L.). Canadian Journal of Botany 71:1182-1192.

I also have a phytolith webpage at http://reled.byu.edu/ascrip/tball/ [this link did not work on 2002/02/20]

Monosilicic acid in the soil, created from the weathering of rocks and the dissolution of biologically deposited SiO2, is taken up by plant roots. Following uptake the acid is transported to various plant organs, where, in many taxa, some of it polymerizes to form solid silica deposits at specific intracellular and extracellular locations (Jones and Handreck, 1967; Raven, 1983; Sangster, 1970). These solid deposits of SiO2, as well as deposits containing calcium compounds, have been given the name "phytolith", literally meaning "plant-rocks." Many plants produce phytoliths with morphological characteristics that appear unique to a given taxon, a phenomenon giving them taxonomic significance.

There has been considerable interest in phytolith research. Phytolith formation and deposition in various cereal grasses has been well documented (Blackman, 1968, 1969; Blackman and Parry, 1968; Hayward and Parry, 1973; Hodson and Sangster, 1989; Hutton and Norrish, 1974; Jones and Handreck, 1965; Kaufman et al., 1972; Soni and Parry, 1973). The role of phytoliths in plant resistance to disease and insects has been investigated (De Silva and Hillis, 1980; Djamin and Pathak, 1967; Hanifa et al., 1974; Jones and Handreck, 1967; Kunoh and Ishizaki, 1975; Lanning, 1966), as well as the detrimental effects phytoliths have on herbivores and humans (Baker, 1961, Baker et al., 1959; Bezeau et al., 1966; Forman and Sauer, 1962; Harbers et al., 1981; O'Neill et al., 1982; Parry and Hodson, 1982; Bhatt et al., 1984). Phytolith research has proved highly valuable to archaeobotanists. Because phytoliths are siliceous, when a plant dies, even if it is burned, buried, or ingested, its phytoliths persist and maintain their morphological integrity, becoming a microfossil of that plant. Microfossil phytoliths have been collected by archaeobotanists from such diverse environments as paleosols exposed by erosion or excavation (Piperno, 1983, 1988), ceramics and bricks made from clay upon which vegetation once grew, or to which plant fibers were added (Rands and Bargielski, paper presented at the 1986 meeting of the Society for American Archaeology) tooth tartar and coproliths of herbivores (Bryant, 1974; Armitage, 1975), and the surface of stone tools used to process plants and/or plant parts (Kamminga, 1979; Anderson, 1980).

Once collected and analyzed, microfossil phytoliths can provide researchers with significant information and insights. Microfossil phytoliths have been used for the reconstruction of paleoenvironments (Fisher et al., 1987; Lewis, 1981; Robinson, 1979; Rovner, 1971; Twiss, 1987), as indicators of ancient industrial and agricultural practices (Liebowitz and Folk, 1980; Piperno, 1984; Rosen, 1992; Rosen, 1999), and for tracing the origins and developments of cultigens (Piperno, 1988). Rovner (1983) in reviewing the value and advances of phytolith research, suggested that it has the potential to become a second palynology. Pearsall (1989) and Piperno (1988) point out that phytolith analysis is especially valuable to archaeobotanists at sites of study were other plant remains are absent. They further indicate that when phytoliths are used in conjunction with other plant remains, they add precision and support for any interpretations made.

References:

Anderson, P.C. 1980.

A testimony of prehistoric tasks: diagnostic residues on stone tool working edges. World archaeology 12: 181-194.

Armitage, P.L. 1975.

The extraction and identification of opal phytoliths from the teeth of ungulates. Journal of Archaeological Science 2: 187-197.

Baker, G. 1961.

Opal phytoliths and adventitious mineral particles in wheat dust. Commonwealth Scientific and Industrial Research Organization, Australia; Mineralgraphic Investigations Technical Paper No. 4, 3-l2.

Baker, G., L.H.P. Jones, & I.D. Wardrop. 1959.

The cause of wear in sheep's teeth. Nature 184: 1583-4.

Bezeau L.M., A. Johnson, & S. Smoliak. 1966.

Silica and protein content of mixed prairie and fescue grassland vegetation and its relationship to the incidence of silica urolithiasis. Canadian Journal of Plant Science 46: 625-631.

Bhatt, T.S., M.M. Coombs, & C.H. O'Neill. 1984.

Biogenic silica fibre promotes carcinogenesis in mouse skin. International Journal of Cancer 34: 519-528.

Blackman, E. 1968.

The pattern and sequence of opaline silica deposition in rye (Secale cereale L.). Annals of Botany 32: 207-218.

Blackman, E. 1969.

Observations on the development of the silica cells of the leaf sheath of wheat (Triticum aestivum). Canadian Journal of Botany 47: 827-838.

Blackman, E. 1971.

Opaline silica bodies in the range grasses of southern Alberta. Canadian Journal of Botany 49: 769-81.

Blackman, E. & D.W. Parry.

1968. Opaline silica deposition in rye (Secale cereale L.). Annals of Botany 32: 199-206.

Bozarth, S.R. 1987.

Diagnostic opal phytoliths from rinds of selected Cucurbita species. American Antiquity 52: 607- 615.

Brown, D. 1984.

Prospects and limits of a phytolith key for grasses in the central United States. Journal of Archaeological Science 11: 221-243.

Bryant, V.M., Jr. 1974.

The role of coprolith analysis in Archaeology. Texas Archaeological Society Bulletin 45: 1-28.

De Silva, D.& W.E. Hillis. 1980.

The contribution of silica to the resistance of wood to marine borers. Holzforschung 34: 95-97.

Dayanandan, P., P.B. Kaufman, & C.I. Franklin. 1983.

Detection of silica in plants. American Journal of Botany 70: 1079-1084.

Djamin, A. & M.D. Pathak. 1967.

Role of silica in resistance to asiatic rice borer, Chilo suppressalis (Walker), in rice varieties. Journal of Economic Entomology 60: 347-351.

Fisher, R.F., M.J. Jenkins, & W.F. Fisher. 1987.

Fire and the prairie-forest mosaic of Devils Tower National Monument. The American Midland Naturalist 117: 250-257.

Forman, S.A. & F. Sauer. 1962.

Some changes in the urine of sheep fed a hay high in silica. Canadian Journal of Animal Science 42: 9-17.

Gould, F.W. & R.B. Shaw. 1983.

Grass Sytematics, 2nd edition, Texas A & M University Press, College Station 226.

Hanifa, A.M., T.R. Subramaniam, & B.W.X. Ponnaiya. 1974.

Role of silica in resistance to the leaf roller, Cnaphalocrocis medinalis Guenee, in rice. Indian Journal of Experimental Biology 12: 463-465.

Harbers, L.H., R.J. Raiten, & G.M. Paulsen. 1981.

The role of plant epidermal silica as a structural inhibitor of rumen microbial digestion in steers. Nutrition Reports International 24: 1057-1066.

Hayward, D.M. & D.W. Parry. 1973.

Electron-probe microanalysis studies of silica deposition in barley (Hordeum sativum L.). Annals of Botany 37: 579-591.

Hodson, M.J. & A.G. Sangster. 1989.

Silica deposition in the inflorescence bracts of wheat (Triticum aestivum). II. X-ray microanalysis and backscattered electron imaging. Canadian Journal of Botany 67: 281-287.

Hutton, J.T. & K. Norrish. 1974.

Silicon content of wheat husks in relation to water transpired. Australian Journal of Agricultural Research 25: 203-212.

Jones, L.H.P. & K.A. Handreck. 1965.

Studies of Silica in the oat plant. III. Uptake of silica from soils by the plant. Plant and Soil 23: 79-96.

Jones, L.H.P. & K.A. Handreck. 1967.

Silica in soils plants and animals. Advances in Agronomy 19: 107-149.

Kamminga, J. 1979.

The nature of use-polish and abrasive smoothing on stone tools. Pp. 143-157 in : Hayden, B. (ed.) Lithic Use-wear Analysis, Academic Press, New York.

Kaufman, P.B., S.L. Soni, J.D. Lacroix, J.J. Rosen, & W.C. Bigelow. 1972.

Electron-probe microanalysis of silicon in the epidermis of rice (Oryza sativa L.) internodes. Planta 104: 10-17.

Kunoh, H. & H. Ishizaki. 1975.

Silicon levels near penetration sites of fungi on wheat, barley, cucumber, and morning glory leaves. Physiological Plant Pathology 5: 283-287.

Lanning, F.C. 1966.

Barley silica: relation of silicon in barley to disease, cold, and pest resistance. Journal of Agriculture and Food Chemistry 14: 636-638.

Lewis, R.O. 1981.

Use of opal phytoliths in paleoenvironmental reconstruction. Journal of Ethnobiology 1: 175-181.

Liebowitz, H. & R.L. Folk. 1980.

Archaeological geology of Tel Yin'am, Galilee, Israel. Journal of Field Archaeology 7: 23-42.

Mulholland, S.C. & G.R. Rapp, Jr. 1989.

Characterization of grass phytoliths for archaeological analysis. Materials Research Bulletin 14: 36-39.

Ollendorf A.L., S.C. Mulholland, & G. Rapp, Jr. 1988.

Phytolith analysis as a means of plant identification: Arundo donax and Phragmites communis. Annals of Botany 61: 209-214.

O'Neill, C.H., Q. Pan, G. Clarke, F.S. Liu, G. Hodges, M. Ge, P. Jordon, Y.M. Chang, R. Newman, & & E. Toulson. 1982.

Silica fragments from millet bran in mucosa surrounding oesophageal tumors in patients in northern China. The Lancet 15(May 29, 1982): 1202-1206.

Parry, D.W. & F. Smithson. 1964.

Types of opaline silica depositions in the leaves of British grasses. Annals of Botany, N.S. 28(109): 169-85.

Parry, D.W. & F. Smithson. 1966.

Opaline silica in the infloresences of some British grasses and cereals. Annals of Botany, N.S. 30(119): 525-38.

Parry, D.W. & M.J. Hodson. 1982.

Silica distribution in the caryopsis and inflorescence bracts of foxtail millet (Setaria italica) and its possible significance in carcinogenesis. Annals of Botan, N.S. 49: 531-540.

Pearsall, D.M. 1978.

Phytolith analysis of archaeological soils: evidence for maize cultivation in formative Equador. Science 199: 177-178.

Pearsall, D.M. 1989.

Paleoethnobotany: A Handbook of Procedures. Academic Press, San Diego.

Piperno, D.R. 1983.

The application of phytolith analysis to the reconstruction of plant subsistence and environments in prehistoric Panama. Ph.D. Dissertation, Temple University.

Piperno, D.R. 1984.

A comparison and differentiation of phytoliths from maize (Zea mays L.) and wild grasses: Use of morphological criteria. American Antiquity 49: 361-383.

Piperno, D.R. 1985.

Phytolith analysis and tropical paleoecology: production and taxonomic significance of siliceous forms in New World plant domesticates and wild species. Review of Paleobotany and Palynology 45: 185-228.

Piperno, D.R. 1988.

Phytoliths analysis: An archaeological and geological perspective. Academic Press, San Diego.

Rapp, G.R., Jr. 1986.

Morphological classification of phytoliths, Pp. 33-35 in: Rovner, I. (ed.) Plant opal phytolith analysis in archaeology and paleoecology, Proceedings of the 1984 Phytolith Research Workshop, North Carolina State University, Raleigh, Occasional Papers No. 1 Raleigh.

Raven, J.A. 1983.

The transport and function of silicon in plants. Biological Reviews of the Cambridge Philosophical Society 58: 179-207.

Robinson, R.L. 1979.

Biosilica analysis: paleoenvironmental reconstruction of 41 LL 254. Appendix III in: Assad, C. & D.R. Porter. An Intensive Archaeological Survey of Enchanted Rock State Natural Area. Center for Archaeological Research Survey Report 84, San Antonio.

Rosen, A.M. 1992.

Preliminary identification of silica skeletons from near eastern archaeological sites: an anatomical approach. Pp. 129-147 in: Mulholland S. & G. Rapp, Jr. (eds.) Phytolith systematics: Emerging issues., Plenum Press, New York.

Rosen, A, 1999.

Phytoliths as indicators of prehistoric irrigation farming, Pp. 193-198 in: Anderson, P.C. (ed.) Prehistory of Agriculture: New Experimental and Ethnographic Approaches. 193-198. UCLA,Institute of Archaeology, Los Angeles.

Rovner, I. 1971.

Potential of opal phytoliths for use in paleoecological reconstruction. Quaternary Research 1: 345-359.

Rovner, I. 1983.

Plant opal phytolith analysis: major advances in archaeobotanical esearch, Pp. 225-266 in: Schiffer, M. (ed.) Advances in Archaeological Method and Theory (6) Academic Press, New York.

Rovner, I. & J.C. Russ. 1992.

Darwin and design in phytolith sytematics: Morphometric methods for mitigating redundancy. Pp. 253-276 in: Mulholland S. & G. Rapp, Jr. (eds.) Phytolith Systematics: Emerging issues. Plenum Press, New York and London.

Russ, J.C. & I. Rovner. 1987.

Stereological verification of Zea phytolith taxonomy. Phytolitharien Newsletter 4: 10-18.

Sangster, A.G. 1970.

Intracellular silica deposition in immature leaves in three species of the Gramineae. Annals of Botany 34: 245-257.

Soni, S.L. & D.W. Parry. 1973.

Electron probe microanalysis of silicon deposition in the inflorescence bracts of the rice plant. (Oryza sativa). American Journal of Botany 60: 111-116.

Twiss, P.C. 1987.

Grass-opal phytoliths as climatic indicators of the Great Plains Pleistocene, Pp. 179-188 in: Johnson, W.C. (ed.) Quaternary Environments of Kansas. Kansas Geological Survey Guidebook Series 5. 179-188.

Twiss, P.C., E. Suess, & R.M. Smith. 1969.

Morphological classification of grass phytoliths. Soil Science Society of America Proceedings 33: 109-115.

PHYTOLITH STUDIES IN WESTERN NORTH AMERICA

Virtues and values of phytolith studies

Phytoliths are silicified replicas of plant cells, which are morphologically distinct, abundant, and durable in soils, loess, cave deposits and other dry environments (Piperno, 1988). Opal phytoliths have been described from many North American plants, mostly grasses and trees, including those in the Pacific Northwest (Norgren, 1973; Klein and Geis, 1978; Brown, 1984; Mulholland, 1989). The phytoliths' main strength is their durability under a wide range of depositional conditions and possibility of identifying plant communities, and sometimes individual taxa, based on matching paleoassemblages with modern analogues. In addition to individual shape counts, phytolith concentrations can be used to infer presence/absence of forested vegetation, as well as to indicate presence of buried A soil horizons (Verma and Rust, 1969; Wilding and Drees, 1971). Most work on phytoliths in North America has focused on archaeological applications, it is only recently that we began to appreciate their large potential for paleoenvironmental reconstructions.

Research approach (extraction, analysis, etc.)

The extraction of phytoliths from plant tissue is done by dry oxidation for a few hours in a muffle furnace at 550 ?C, by wet oxidation with a heated strong acid, or combined wet and dry oxidation (Pearsall, 2001). In my work I use modified method of Piperno (1988, modified in Blinnikov, 1999) for extraction of phytoliths from soils. Phytoliths can be quantitatively extracted from the silt fraction of soil or loess (5-100 microns, 20-50 g of soil per sample). After soil fractionation and removal of clay and sand, the organics are removed by a concentrated (70% or more) nitric acid with a pinch of potassium perchlorate added per 50 ml test tube. Carbonates are removed by mild hydrochloric acid. Opal fraction (phytoliths) is be separated from quartz and other heavier minerals using flotation in sodium polytungstate or zinc bromide solution (specific gravity of 2.3 g/cm3). Concentration of phytoliths is calculated based on the ratio of the total dry weight of the opal residue to the total dry weight of the initial sample. Information about vegetation composition can be then obtained based on identification of individual phytolith shapes from fossil samples under a light microscope and matching the paleoassemblages against a reference collection from modern plants and soils by using squared chord distance approach and detrended correspondence analysis, or similar multivariate techniques.

Phytoliths in western North America

While there exists a considerable bibliography on phytolith research worldwide (Runge, 1998), little work has been reported from western North America. Some early works include Witty and Knox (1964), Blackman (1971), Norgren (1973) and Bombin (1984). More recently, Blinnikov et al. (2001a, 2001b) demonstrated that phytoliths leave distinct signatures under eight main types of the forest and steppe communities of the Columbia Basin, WA. Specifically, ponderosa pine forests can be easily distinguished based on the presence of diagnostic ponderosa pine "spiny body" phytolith (see Kerns, 2001 for illustration and details). Fir and spruce-dominated forests can be distinguished based on presence of silicified tracheids and blocky cells of spruce. Potential also exists in distinguishing Douglas-fir dominated forests based on diagnostic branched asterosclereids of Pseudotsuga (Norgren, 1973).

Blinnikov et al. (2001a) also suggests that phytolith assemblages of three types of grassland and a shrub steppe can be differentiated. Because almost all of the northwestern US grasses are C3 species producing mostly festucoid rondels, the classical scheme of Twiss et al. (1969) differentiating between panicoids, chloridoids and festucoids, is of little use. However, we found that drier Agropyron-Poa dominated grasslands have on average much smaller percentage of rondels than more mesic Festuca-Koeleria dominated grasslands. Furthermore, any grasslands with the presence of Stipa s.l. will be differentiated based on the presence of distinct Stipa-type bilobate form which is different from "classical" panicoid bilobates. Aristida spp. can be distinguished based on long-shafted bilobate bodies also described from Aristida in Arizona and Australia (Kerns, 2001; Bowdery, 1998). Finer distinctions between, e.g., Koeleria and Poa, or between Calamagrostis and Bromus may be achieved (Kerns, 2001; Blinnikov, 1994). Shrublands with presence of Artemisia tridentata and related sagebrush species can be separated based on the presence of abundant blocky forms and fragments of silicified sinuous epidermis common among dicots, but not grasses. Communities overrun by cheat brome (Bromus tectorum) could be distinguished based on high percentage of silicified epidermis forms is soils, common also in domesticated grasses.

Little work has been done with phytoliths from western North American wetlands, but studies of sedge phytoliths in Russia and the Mid-West of the US (Bobrov et al., 2001; Ollendorf, 1992) suggest that some sedges can be distinguished based on their phytoliths. Bozarth (1993) and other authors suggest that other phytolith producers among temperate species include nettles, elms, oaks, sunflower family and other dicots.

Overall it appears that opal phytoliths can make the most valuable contribution when used in combination with other proxy sources of paleoenvironmental data, such as pollen, stomata, macrofossils, charcoal, and isotope analysis. Due to considerable redundancy and multiplicity of individual phytolith shapes it is overall unlikely that we will ever be able to identify individual species of plants based solely on their phytoliths. Differentiation of some genera of grasses (Koeleria, Calamagrostis, Festuca, Poa, Stipa, Aristida) and subgeneric level identifications in sedges are, on the other hand, entirely possible. More productive seems to be to search for unique community signatures in soils based on all plants found in a particular ecosystem.

Phytoliths in western US can provide valuable information about the history of paleoenvironments. Some directions of future work should include:

1. enlarging regional phytolith collection both from individual species and signatures from soils under distinct native and non-native plant communities
2. fine-tuning existing phytolith classifications for the region to include all major phytolith morphotypes from grasses, forbs, and trees
3. expanding paleoenvironmental phytolith research into British Columbia, Alberta, and Alaska
4. analyzing phytoliths from forested environments and wetlands in greater detail
5. doing fine scale phytolith studies to resolve local variability, taphonomy and post- depositional transport issues
6. exploring possibility of using phytoliths as a direct proxy for paleoclimates bypassing vegetation reconstructions by using transfer functions, similarly to how it is done with pollen (e.g., Webb et al., 1998; see a Phytolith-related attempt in Fredlund and Tieszen, 1997), or stable isotope analysis (Stevenson, 1997).

References

Blackman, E. 1971.

Opaline silica bodies in the range grasses of southern Alberta. Canadian Journal of Botany 49: 769-781.

Blinnikov, M. 1994.

Phytolith analysis and the Holocene dynamics of alpine vegetation. Pp. 23-40 in: Onipchenko, V. & M. Blinnikov (eds.) Experimental Investigation of Alpine Plant Communities in the Northwestern Caucasus. Veroffentlichungen des Geobotanischen Institutes der ETH, Stiftung Rbel, Zurich, H. 115.

Blinnikov, M., A. Busacca, & C. Whitlock. (2001a, in press).

Reconstruction of the Late Pleistocene Columbia Basin Grassland, Washington, USA, Based on Phytolith Records in Loess. Palaeogeography, Palaeoclimatology, Palaeoecology 2714: 1-25.

Blinnikov, M., A. Busacca, & C. Whitlock. 2001b.

A new 100,000-yr. record from the Columbia Basin, Washington, USA. Pp. 27- 55 in: J. D. Meunier, J.D. & F. Colin (eds.) Phytoliths: Applications in earth sciences and human history. A. A. Balkema, Rotterdam, the Netherlands.

Bobrov, A. A., Bobrova, E. K., Alexeev Ju. E. 2001.

Biogenic silica in biosystematics: potential uses. Pp. 279-288 in: Meunier J.D. & F. Colin (eds.) Phytoliths: Applications in Earth Sciences and Human History. A. A. Balkema, Rotterdam, the Netherlands.

Bowdery, D. 1998.

Phytolith Analysis Applied to Pleistocene-Holocene Archaeological Sites in the Australian Arid Zone. British Archaeological Reports International Series, v. 695.

Bozarth, S. R. 1993.

Biosilicate assemblages of boreal forests and aspen parklands. Pp. 95-105 in: Pearsall, D.M. & D.R. Piperno (eds.) Current Research in Phytolith Analysis: Applications in Archaeology and Paleoecology MASCA Research Papers in Science and Archaeology, Volume 10.

Brown, D. 1984.

Prospects and limits of a Phytolith key for grasses in the central United States. Journal of Archaeological Sciences 11: 345-368.

Bombin, M. 1984.

On phytoliths, late Quaternary ecology of Beringia, and information evolutionary theory. Unpublished Ph.D. dissertation, University of Alberta, Calgary, Alberta, Canada. 163 p.

Fredlund, G. G., & L.L. Tieszen. 1997.

Calibrating grass phytolith assemblages in climatic terms: Application to late Pleistocene assemblages from Kansas and Nebraska. Palaeogeography, Palaeoclimatology, Palaeoecology 136: 199-211.

Kearns, B. 2001.

Diagnostic phytoliths for a ponderosa pine-bunchgrass community near Flagstaff, Arizona. The Southwestern Naturalist 46(2): 282-294.

Klein, R. L., & J.W. Geis. 1978.

Biogenetic opal in the Pinaceae. Soil Science 126: 145-156.

Mulholland, S. C. 1989.

Phytolith shape frequencies in North Dakota grasses: a comparison to general patterns. Journal of Archaeological Science 16: 489-511.

Norgren, J. A. 1973.

Distribution, Form and Significance of Plant Opal in Oregon Soils. Ph.D. dissertation, Oregon State University, Corvallis, OR.

Ollendorf, A. L. 1992.

Toward a classification scheme of sedge (Cyperaceae) phytoliths. Pp. 91-106 in: Mulholland S. & G. Rapp, Jr. (eds.) Phytolith Systematics: Emerging issues. Plenum Press, New York, NY.

Pearsall, D. 2001.

Paleoethnobotany: A Handbook of Procedrues. 2nd ed. Academic Press, San Diego, CA.

Piperno, D. 1988.

Phytolith Analysis: An Archeological and Geological Perspective. Academic Press, San Diego, CA.

Runge, F. 1998.

Bibliography of Phytolith Research. University of Paderborn, Germany.

Stevenson, B. A. 1997.

Stable Carbon and Oxygen Isotopes in Soils and Paleosols of the Palouse Loess, Eastern Washington State: Modern Relationships and Applications for Paleoclimatic Reconstruction. Unpublished Ph.D. dissertation, Colorado State University, Fort Collins, CO.

Twiss, P.C., Suess,C.E., and Smith, R.M. 1969.

Morphological classification of grass phytoliths. Soil Science Society of America Proceedings 33: 109-115.

Verma, S. D. & R. H. Rust. 1969.

Observation on opal phytoliths in a soil biosequence in southeastern Minnesota. Soil Sci. Soc. America Proc. 33: 749-751.

Webb, T. III, K.H. Anderson, P.J. Bartlein, & R.S. Webb. 1998.

Late Quaternary climate change in eastern North America: a comparison of pollen-derived estimates with climate model results. Quaternary Science Reviews 17: 587-606.

Wilding, L. P. & L.R. Drees. 1971.

Biogenic opal in Ohio soils. Soil Sci. Soc. America Proc. 35: 1004-1010.

Witty, J. E. & E.G. Knox, E. G. 1964.

Grass opal in some Chestnut and Forest soils in north central Oregon. Soil Science Society of America Proceedings 28: 685-687.

Mikhail Blinnikov's phytolith gallery: http://coss.stcloudstate.edu/mblinnikov/phd/phyt.html

Terry Ball's phytolith page: http://reled.byu.edu/ascript/tball/index2.html [this link did not work on 2002/02/20]

Deb Pearsal's phytolith web site: http://web.missouri.edu/~phyto/

University of Arizona phytolith links: http://www.geo.arizona.edu/palynology/pphyolth.html

Glen Fredlund's webpage: http://www.uwm.edu/People//fredlund/phytocat.htm

ULTIMATE PALINDROME?

Dear Adolf:

Here's a true challenge. I think you should rush to press at 8:02 pm tonight! Here is an interesting palindrome as the excuse (which I got from my stepbrother who got from someone else .... etc!):

Believe it or not, 8.02pm on February 20 this year will be an historic moment in time. It will not be marked by the chiming of any clocks or theringing of bells, but at that precise time, on that specific date, something will happen which has not occurred for 1,001 years and will never happen again. As the clock ticks over from 8.01pm on Wednesday, February 20, time will, for sixty seconds only, read in perfect symmetry 2002, 2002, 2002, or to be more precise - 20:02, 20/02, 2002. The last occasion that time read in such a symmetrical pattern was long before the days of the digital watch and the 24-hour clock at 10.01am on January 10, 1001. And because the clock only goes up to 23.59, it is something that will NEVER happen again.

Sorry, Scott!
At this palindromic moment we will be [again] in Portland, Oregon, and I will be sipping Pilsener Urquell with Oluna and my friends in the Rheinlander. - Adolf

P.S. When I looked at the date posted in BEN, I realized that I have not changed the year in the two previous BEN issues and they are labelled as "2001". Can you change it in the web page? Thanks. - AC

Web-ed's note: Done. Regarding the ultimate palindrome, the ultimate part is true only of the millennium problem, and there has been A LOT of correspondence on this. As many have noticed, it is not so ultimate, as three more centenary dates will work, and there is a yearly component, too. I am sure Adolf will have more on this! -SR