The fine structure of the perineural endothelium

Summary Fine strands of motor nerves were examined with the electron microscope using thin section as well as freeze-etching techniques. The specimens were taken from frog cutaneous pectoris nerve, rat sciatic nerve, mouse and shrew phrenic nerves and from human skin nerves. The perineural sheath (Henle, Ranvier, Key and Retzius) consists of one to several concentric laminae of endothelial cells; it encases nerve fascicles and eventually individual nerve fibers and terminals. The endothelial cells are extremely thin and fitted together smoothly by overlap and dove-tailing of their border zones. The cell contacts are formed by continuous zonulae occludentes, often reinforced by maculae adhaerentes, and in depth they comprise 3–15 strands with an average of 5–6 strands per junction. The membranes of endothelial cells are studded with attachment sites and stomata of plasmalemmal vesicles suggesting a high level of pinocytotic activity. This phenomenon is by no means restricted to the external laminae of the endothelial sheath. Each endothelial lamina is vested with basement membranes on both (epineural and endoneural) sides, and the spaces between laminae contain a few collagen fibers and fibroblasts. Occasionally, punctate tight junctions are seen between laminae. Cytological evidence supports the hypothesis that the perineural endothelium provides a relatively tight and highly selective barrier separating the peripheral nerves from surrounding tissue and its extracellular fluid spaces. This effect is achieved on the one hand by the sealing of pericellular spaces and on the other hand by a membrane controlled transcellular transport mechanism (pinocytosis), both of which are enhanced by their serial arrangement.Dedicated to Professor Wolfgang Bargmann, Kiel, on the occasion of his 70th birthday.The technical assistance of Dr. F. Dreyer, Mr. D. Savini, Miss H. Claassen and Miss R. Emch is gratefully acknowledged.Financial support was received by the following institutions: Swiss National Foundation for Scientific Research, grants Nrs. 3.368.0.74, 3.774.72, 3.259.74, 3.045.73. Deutsche Forschungsgemeinschaft (Sonderforschungsbereich 38, Projekt N). The Dr. Eric Slack-Gyr Stiftung in Zürich and the Hartmann-Müller Stiftung for Medical Research in Zürich.     

Specific arrangements of membrane particles at sites of exo-endocytosis in the freeze-etched neurohypophysis

Summary Images have been obtained from freeze-etch replicas of neurohypophyses which are consistent with the view that orderly arranged aggregates of membrane particles occur in regions where fragments of membrane are being added to and taken away from the plasma membrane during secretion. Aggregates of particles included rosette-like and necklace-like patterns similar to those described by other authors at sites of exocytosis and endocytosis.Dedicated to Prof. W. Bargmann at the occasion of his 70th birthday. A short account has been presented at the 8th International Congress of Electron Microscopy (Dreifuss, Akert, Sandri and Moor, 1974).This work was supported by grants from the Swiss National Foundation for Scientific Research Nos. 3.257.74, 3.368.0.74, 3.774.72 and 3.045.73; the Hartmann-Müller Foundation for Medical Research in Zürich and the Dr. Eric Slack-Gyr Stiftung.     

Freeze-etch study of the teleostean pituitary

Summary The structure of membranes in the pituitary of several teleostean species was studied with the freeze-etching technique. Nuclear pore density is higher in hormone-secreting than in stellate cells, suggesting a higher rate of nucleo-cytoplasmic interactions in the secretory cells. The perinuclear endoplasmic reticulum (ER) in the MSH-secreting cells has a large number of fenestrae, whereas in the ER whorls of the prolactin-secreting cells the fenestration occurs only rarely. Three different types of membrane specializations are described, presumably related to exo-endocytotic events at the level of the plasmalemma.The Following Abbreviations are used in the Present Study AH adenohypophysis - ER endoplasmic reticulum - ES extravascular spaces - FE freeze-etching - HRP horseradish peroxidase - NH neurohypophysis - NS neurosecretory - SG secretory granule This work was supported by grants from the Swiss National Science Foundation Nos. 3.636.75, 3.611.75 and the Dr. Eric Slack-Gyr Stiftung in Zürich     

Citrate transport into barley mesophyll vacuoles — comparison with malate-uptake activity

Citrate uptake into barley (Hordeum vulgare L.) mesophyll vacuoles was found to be saturable with a K _m of about 200 M. Uptake appears to occur via the citrate^3- form, as indicated by concentration-dependent uptake studies at different pHs. Free citrate and not the Mg-citrate complex was taken up by the vacuoles, even though slow transport of the Mg complex could not be excluded. Citrate transport into vacuoles was competitively inhibited by malate (K _i=0.68 mM). Various organic acids and protein-modifying agents affected the uptake of malate and citrate to a similar extent. These results indicate that both organic acids cross the tonoplast by means of the same carrier. Accumulation of citrate was ATP-dependent and could be inhibited by ionophores. Bovine serum albumin strongly stimulated citrate uptake, but other proteins tested did not show a similar stimulatory effect.Abbreviation BSA bovine serum albumin We wish to thank Esther Vogt for her help with the experiments and Professor N. Amrhein (ETH, Zürich, Switzerland) and Dr. Michael Kertesz (ETH, Zürich) for helpful discussions. This work was supported by the Swiss National Foundation grant No. 31-25196.88.     

Localization of the gene for the vitamin B12 binding protein,transcobalamin II,near the centromere on mouse chromosome 11, linked with the hemoglobin alpha-chain locus

Somatic cell hybrids, recombinant inbred (RI) mouse strains, and backcross breeding experiments were used to locate the gene of transcobalamin II (Tcn-2), the vitamin B12 binding protein in mouse serum. TCN-2 was found to be a useful genetic marker in the somatic cell hybrids. Selected hybrid clones were derived from fusions between GR mouse cells and the Chinese hamster cell line E36. Analysis of mouse specific chromosomal enzyme markers in relationship to TCN-2 secretion, in the hybrid clones, provided provisional evidence for assignment of the Tcn-2 locus to chromosome 11. The strain distribution pattern of the TCN-2 variants S and F in the RI series CXS, constructed from the cross of BALB/cHeA (TCN-2S) with STS/A (TCN-2F), implied a close linkage with the hemoglobin alpha-chain locus (Hba) on chromosome 11. Backcross breeding using inbred strains confirmed these findings and located the Tcn-2 gene closest to the centromere, linked with waved 2 (wa-2) and Hba with recombination frequencies of 6.9 and 19.2% each. The linkage group Tcn-2/wa-2/Hba was established.This work was supported by Swiss National Science Foundation Grants 3.023-0.81 and 3.728-0.80, Fritz Hoffmann-La Roche Stiftung 173, the Prof. Dr. Max Cloëtta Foundation, and the Kantonale Zürcher Liga für krebsbekämpfung, Switzerland. M. Prochazka was supported by the Postgraduate Training Program for Experimental Medicine and Biology of the University of Zürich, Switzerland.     

Fertilization in Fucus

Summary Methods are described for the collection, treatment and uniform discharge of large quantities of gametes, and a measure of fertilization control in the monoecious brown alga, Fucus distichus. Fertilization was examined using the techniques of blister-formation, gamete separation experiments, and electron microscopy. Sperm enter the freshly-discharged egg packets through a mesochite pore and juxtaposition with the eggs early. However, experimental and thinsection data indicate that fertilization does not occur until the eggs dissociate from the mesochite and round up. Hence, the egg surface appears to undergo three functional changes following its release from the thallus: (1) a pre-dissociation state which inhibits fertilization within the mesochite; (2) a dissociation state when fusion of gametes is possible; and (3) a post-fertilization state characterized by the formation of extraneous coats. As the egg is activated by the sperm a nonmembranous layer appears to detach from the egg surface to form an activation layer. This is augmented by fibrous units to function as a fertilization barrier which ultimately thickens to form the cell wall. The area between the eggs within the egg packet is characterized by the presence of fibrous and particulate substances which are continuously given off through the egg surface. These apparently play a functional role in the sequential stages of fertilization in Fucus. These observations are discussed in terms of analogies with fertilization in the sea urchin.This work was supported by a Lalor Foundation Research Fellowship at Friday Harbor Biological Laboratories, University of Washington, and by a National Science Foundation Science Faculty Fellowship to the Swiss Federal Institute of Technology, Zürich, Switzerland.     

Age specific fecundity and size of offspring in the prosobranch snail,Viviparus ater

Summary Age specific fecundity and size of offspring were compared in two populations of Viviparus ater, one from Lake Zürich (Switzerland) and one from Lake Maggiore (Italy). Females were caged and their offspring sampled at weekly intervals. Average fecundity per female over one year was 19.6 and 14.7 offspring in Lake Zürich and Lake Maggiore, respectively. Average shell widths of offspring at birth in the two lakes were 8.5 mm and 7.4 mm. Fecundity did not change with age in Lake Zürich but decreased with increasing age of the snails in Lake Maggiore. Fecundity and offspring size were positively correlated with the size of the females in both lakes, but fecundity was higher and offspring were larger in Lake Zürich than in Lake Maggiore irrespective of the size of the females. An analysis of covariance, correcting for differences between the two lakes in the total fresh weight of the offspring produced annually, showed that females from the two lakes distributed their reproductive investment differently. Females in Lake Zürich produced relatively fewer but larger offspring than females in Lake Maggiore. This trade-off was hidden because females in Lake Zürich produced twice as much offspring biomass as females in Lake Maggiore. The possibility that different selection regimes might account for the observed differences is discussed.     

Reappearance of hydrolytic activities and tonoplast proteins in the regenerated vacuole of evacuolated protoplasts

Mesophyll protoplasts of tobacco (Nicotiana tabacum L. cv. Xanthi) were evacuolated by centrifugation in a density gradient. Evacuolation resulted in the quantitative loss of vacuolar hydrolytic activities. The evacuolated miniprotoplasts were cultivated under different conditions, and the regeneration of the central vacuole was investigated by light and electron microscopy as well as by the determination of activities of vacuolar marker enzymes. Vacuoles and hydrolytic activities, as well as cell wall material reappeared faster when the cells were cultivated at low osmotic strength. A newly synthesized tonoplast polypeptide could be detected using a polyspecific serum raised against tonoplast proteins of barley (Hordeum vulgare L.). Both vacuolar proton pumps, the ATPase as well as the pyrophosphatase appear to be newly synthesized during the regeneration of the vacuole.Abbreviations GAP-DH NADP-dependent glyceraldehyde 3-phosphate dehydrogenase - PEP phosphoenolpyruvate - PPi pyrophosphate - PPase pyrophosphatase We thank Dr. Ernst Wehrli, Labor für Elektronenmikroskopie I, ETH Zürich, for taking micrographs. Esther Vogt assisted in the determination of the hydrolases. Bafilomycin was kindly provided by Professor Altendorf, Osnabrück FRG. This work was supported by the Swiss National Foundation grant No. 31-25196.88.     

Reproductive effort and growth in the prosobranch snail,Viviparus ater

Summary We compared two populations of Viviparus ater from Lake Zürich and Lake Maggiore with respect to the reproductive investment of individual females throughout their lives. Based on field observations of the bumber and size of offspring and from measurements of the differences between growth rings on the shells we constructed a probabilistic model for the life history of the females. A simulation showed that the overall productivity of females was higher in Lake Zürich than in Lake Maggiore. The higher productivity of females in Lake Zürich was due to faster growth before maturity and higher fecundity after maturity. The reproductive effort, as measured by the percentage of assimulated energy used for reproduction, remained constant throughout the life of the females in Lake Zürich, whereas it declined with age in Lake Maggiore. We interpret this as the outcome of a reproductive strategy that avoids risks due to reckless reproduction, rather than as two different strategies which have been selected in response to different habitat types.     

Neuritic growth cone and ependymal gap junctions in the feline subfornical organ during early development

Summary Intercellular contacts in the subfornical organ (SFO) of kittens 3, 16, and 29 days old were studied in thin sections and by the freeze-etch method. Gap junctions appeared between growing nerve processes and target cells. The junctions were interspersed between immature synapses lacking mitochondria as well as full preand postsynaptic membrane specializations. Gap junctions were seen on filopodia as well as on more mature processes. The morphology of these junctions was typical of those described earlier but they were of small size (0.2–0.3 m).Gap junctions of peculiar form were also seen between ependymal elements in the SFO at 16 days. These were of large size (0.5–0.8 m) and were often of segmented character. This segmentation consisted of bands 3–4 particles in width with a center-to-center spacing of 90 nm with particle free corridors between corresponding to the width of about two rows of particles. The margin of the group might be circumscribed by a row of particles. Although gap junctions of large size were seen between ependymal cells in thin section, features corresponding to the particle free corridors have not been observed to date.On leave of absence from the National Institute of Neurological and Communicative Disorders and Stroke, Section of Functional Neurosurgery, Branch of Clinical Neuroscience, Bethesda, Maryland 20014, USAThis work was supported by grants from the Swiss National Foundation for Scientific Research Nos. 3.636.76 and 3.611.0.75, the EMDO Stiftung and the Dr. Eric Slack-Gyr Stiftung     

Quantitative analysis of squamous epithelium of normal palatal mucosa in guinea pigs

Summary The epithelium of intact guinea pig palate was subjected to stereologic analysis in a study of structural alterations in the keratinizing epithelium in response to wounding. Point counting procedures were employed to analyse electron micrographs sampled from three epithelial strata in biopsies collected from five animals. The differentiation pattern of the guinea pig palate epithelium displayed the following structural density gradients from basal to granular layers: descending gradients of metabolically active organelles, ascending gradient of bundled filaments coupled with the appearence of membrane coating granules and keratohyalin granules, and a plateau-like gradient of cytoplasmic ground substance. This pattern of epithelial differentiation is basically identical to that of human hard palate epithelium and epidermis. Regional and species variations in structure of keratinizing epithelia are suggested based on interepithelial differences in morphometric parameters.This investigation was supported in part by grant No. 512-4064 from the Danish State Medical Research Council and by a grant from the Calcin Foundation.The data recording and computation was performed on a guest visit at the Dental Institute, University of Zürich.     

Zellphysiologische Mechanismen bei der Regulation von Genaktivitäten in den Riesenchromosomen von Chironomus thummi

Ohne ZusammenfassungTeil einer Habilitationsschrift an der Eidg. Technischen Hochschule, Zürich. Das Original kann in der Hauptbibliothek eingesehen werden.Ich danke Herrn dipl. Natw. ETH M. Lezzi und Frl. H. Roloff für mannigfache sorgfältige Hilfe. Die Arbeit wurde unterstützt vom Schweizerischen Nationalfonds zur Förderung der wissenschaftlichen Forschung und vom Damon Runyon Memorial Fund for Cancer Research (DRG-668).     

Analysis of allergens in ambient aerosols: Comparison of areas subjected to different levels of air pollution

Recent studies describe interactions of pollen surfaces with aerosol particles; pollen surfaces undergo morphological changes and the release of allergens and allergenic fragments from the pollen can be enhanced. Thus allergens from pollen can be found in particle size fractions much smaller than undamaged pollen (<5m). This may explain allergic reactions in parts of the lungs which cannot be reached by undamaged pollen. In Switzerland the birch tree (betula verrucosa) major allergen Bet v 1 and the grass (phleum pratense) pollen major allergen Phl p 5 are of particular relevance for inducing pollinosis. In this study aerosols of different aerodynamic diameters were sampled by Andersen-Impactors over 18 months. Sampling areas are subjected to different levels of air pollution (Zürich, Switzerland, urban; Payerne, Switzerland, rural: Davos, Switzerland, alpine). Samples were scanned by electron microscopy and submitted to specific allergen assays (ELISA) for birch pollen major allergen Bet v 1 and grass pollen major allergen Phl p 5 respectively. Particle and major allergen concentrations were highest in Zürich, followed by Payerne and, significantly lower, Davos. Scanning electron microscopy investigations showed interactions of aerosols with pollen surfaces in Zürich and Payerne. The presence of Bet v 1 in smaller aerosol fractions was demonstrated in Zürich and Payerne some weeks before and after birch pollen was counted.     

Structure and ultrastructure of the frog motor endplate

Summary The frog motor endplate in its simplest form consists of an elongated, slender nerve ending embedded in a gutter-like depression of the sarcolemma. This nerve terminal contains the usual synaptic organelles. It is covered by a thin coating of Schwann cell cytoplasm which embraces the terminal with thin finger-like processes from both sides, thereby sub-dividing it into 300–1000 regularly spaced compartments. The individual synaptic compartments correspond to the strings of varicosities or grape-like configurations of motor nerve terminals in endplates of other species and in the cerebral neuropil of vertebrates.Each compartment contains one or more bar-like densities of the presynaptic membrane, active zones, which are associated with the attachment sites between synaptic vesicles and plasmalemma. Active zones have a regular transverse arrangement and occur at specific loci opposite the junctional folds. The attachment sites for synaptic vesicles are at the edges of the bars which are bilaterally delineated by a double row of 10 nm particles attached to the A-face. The structural appearance of vesicle attachment sites in freeze-etch replicas corresponds to that of micropinocytosis. The active zones are often fragmented and the frequency of their association with vesicle attachment sites is highly variable.The junctional folds are characterized by specific sites in which intramembranous particle aggregations occur at relatively high packing density (7500/m²). These sites are located opposite the active zones at the juxtaneural lips, a location where one would expect ACh-sensitive receptors on the postsynaptic membrane.This work was supported by the Deutsche Forschungsgemeinschaft (Sonderforschungsbereich 38, Projekt N), The Swiss National Foundation for Scientific Research (Grants Nr. 3 82372 and 3 77472) and the Dr. Eric Slack-Gyr Foundation Zürich.     

Intercellular junctions of antennal gland epithelial cells in the crayfish,Orconectes virilis

Summary Labyrinth and nephridial canal cells of the crayfish (Orconectes virilis) antennal gland possess two types of intercellular junctions revealed by freeze-fracture studies. Apical margins of the cells are connected by long septate junctions. In replicas, these junctions consist of many parallel rows of 80–140 Å intramembrane particles situated on the PF membrane face (EF and PF fracture faces of Branton et al., 1975). Rows of pits are found on the EF fracture face and are deemed complementary to the rows of particles. Moreover, lateral margins of basal regions of the epithelial cells are attached by many intercellular junctions. These contacts are characterized in thin plastic sections by a narrow dense cytoplasmic plaque located subjacent to the plasma membrane at sites of adjoined cells, and 5 to 12 fine strands of dense material that extend across the intercellular gap between adjoined cells. In freeze-fracture replicas, EF intramembrane faces basal to the region of the plasma membrane containing septate junctions exhibit numerous discoid clusters of particles. The particle aggregates, assumed to represent freeze-cleave images of adhering junctions, range from 900 to 3,700 Å in diameter, with individual particles about 185 Å in diameter. These junctions appear to connect epithelial cell processes formed by basal infoldings of the plasma-lemma, and occur between adjacent cells as well as adjacent processes of a single cell. The discrete aggregates of particles resemble replicated desmosomes (Shienvold and Kelly, 1974) and hemi-desmosomes (Shivers, 1976); therefore, they probably do not constitute a basis for electrical coupling between antennal gland epithelial cells.Supported by the National Research Council of Canada     

A quantitative electron microscopic analysis of the keratinizing epithelium of normal human hard palate

Summary The epithelium of normal human hard palate was subjected to stereologic analysis. Ten biopsies were selected from a total of twenty specimens collected from 9 to 16 year old females, and processed for light- and electron microscopy. At two levels of magnification, electron micrographs were sampled from three strata (basale, spinosum, granulosum) in two locations (epithelial ridges and portions over connective tissue papillae). Stereologic point counting procedures were employed to analyse a total 1560 electron micrographs. In general, the thickness of the palate epithelium was 0.12 mm (over papillae) and 0.31 mm (in ridges), the epithelium is distinctly stratified, and homogeneously ortho-keratinized. From basal to granular layers, the composition of strata revealed decreasing densities of nuclei, mitochondria, membrane-bound organelles and aggregates of free ribosomes. Keratohyalin bodies and membrane coating granules increased, and cytoplasmic filaments with a constant diameter of about 85 Å increased from 14 to 30% of cytoplasmic unit volume. The cytoplasmic ground substance occupied a stable 50% of the epithelial cytoplasm in all strata. The composition of basal layers in ridges differed from that over connective tissue papillae. The data are discussed in relation to the observations that (1) an increasing gradient of filament density is not the most characteristic feature of ortho-keratinizing oral epithelium and (2) differences in the degree of differentiation in cells of the stratum basale coincided with the comparable frequency distribution pattern of dividing cells.The authors are thankful to Miss K. Rossinsky for excellent technical assistance, to Mrs. M. Graf-de Beer for competent data computation and to Mrs. S. Münzel-Pedrazzoli for help in morphometric analysis. This study was in part supported by Grants Nos. 51 and 106 of the Hartmann Müller Foundation and by a Grant from the Foundation of Scientific Research at the University of Zürich.     

Na+/H+-exchange in A6 cells: Polarity and vasopressin regulation

Summary We have analyzed the mechanism of Na⁺-dependent pH_i; recovery from an acid load in A6 cells (an amphibian distal nephron cell line) by using the intracellular pH indicator 27-bis(2-carboxyethyl)5, 6 carboxyfluorescein (BCECF) and single cell microspectrofluorometry. A6 cells were found to express Na⁺/H⁺-exchange activity only on the basolateral membrane: Na⁺/H⁺-exchange activity follows simple saturation kinetics with an apparent K _mfor Na⁺ of approximately 11 mm; it is inhibited in a competitive manner by ethylisopropylamiloride (EIPA). This Na⁺/H⁺-exchange activity is inhibited by pharmacological activation of protein kinase A (PKA) as well as of protein kinase C (PKC). Addition of arginine vasopressin (AVP) either at low (subnanomolar) or at high (micromolar) concentrations inhibits Na⁺/H⁺-exchange activity; AVP stimulates IP₃ production at low concentrations, whereas much higher concentrations are required to stimualte cAMP formation. These findings suggest that in A6 cells (i) Na⁺/H⁺-exchange is located in the basolateral membrane and (ii) PKC activation (heralded by IP₃ turnover) is likely to be the mediator of AVP action at low AVP concentrations.This work was supported by the Swiss National Science Foundation (Grant No. 32-30785.91), the Stiftung für wissenschaftliche Forschung an der Universität Zürich, the Hartmann-Müller Stiftung, the Sandoz-Stiftung, the Roche Research Foundation, and the Geigy Jubiläumsstiftung. Prof. Dr. V. Casavola and Dr. R. Guerra were supported by a research grant, No. 91.02470.CT14 of the Consiglio Nazionale della Ricerche (C.N.R.) We are grateful to Prof. Dr. B.C. Rossier of the Institute of Pharmacology of Lausanne (Switzerland) for the gift of the A6 cells, to H.P. Gaeggeler for the supply of the necessary culture media and to Jutka Forgo for her excellent help in the day-to-day culturing of the A6 cells. The secretarial assistance of D. Rossi is gratefully acknowledged.     

Apical and basolateral Na/H exchange in cultured murine proximal tubule cells (MCT): Effect of parathyroid hormone (PTH)

Summary Kidney proximal tubule Na/H exchange is inhibited by PTH. To analyze further the cellular mechanisms involved in this regulation we have used MCT cells (a culture of SV-40 immortalized mouse cortical tubule cells) grown on permeant filter supports. Na/H exchange was measured using single cell fluorescence microscopy (BCECF) and phosphate transport (measured for comparisons) by tracer techniques. MCT cells express apical and basolateral Na/H exchangers which respond differently to inhibition by ethylisopropylamiloride and by dimethylamiloride, the basolateral membrane transporter being more sensitive. Apical membrane Na/H exchange was inhibited by PTH (10^–8 m; by an average of 25%); similar degrees of inhibition were observed when cells were exposed either to forskolin, 8-bromo-cAMP or phorbol ester. Basolateral membrane Na/H exchange was stimulated either by incubation with PTH (to 129% above control levels) or by addition of phorbol ester (to 120% above control levels); it was inhibited after exposure to either forskolin or 8-bromo-cAMP. The above effects of PTH and phorbol ester (apical and basolateral) were prevented by preincubation of cells with protein kinase C antagonists, staurosporine and calphostin C; both compounds did not affect forskolin or 8-bromo-cAMP induced effects. PTH also inhibited apical Na-dependent phosphate influx (29% inhibition at 10^–8 m); it had no effect on basolateral phosphate fluxes (Na-dependent and Na-independent). Incubation with PTH (10^–8 m) resulted in a rapid and transient increase in [Ca²⁺] _i (measured with the fluorescent indicator, fura-2), due to stimulation of a Ca²⁺ release from intracellular stores. Exposure of MCT cells to PTH did not elevate cellular levels of cAMP. Taken together, these results suggest that PTH utilizes in MCT cells the phospholipase C/protein kinase C pathway to differently control Na/H exchangers (apical vs. basolateral) and to inhibit apical Na/P _i cotransport.This work was supported by the Swiss National Science Foundation (Grant No. 32-30785.91), the Stiftung für wissenschaftliche Forschung an der Universität Zürich, the Hartmann-Müller Stiftung, the Sandoz-Stiftung, the Roche Research Foundation and the Geigy-Jubiläumsstiftung. We are grateful to Denise Rossi and Christa Knellwolf for their excellent secretarial assistance.     

Simulating the development of peat bogs

Summary A dynamic model is developed which simulates changes in peat bogs on different kinds of slopes. The relationships between the elements of the model which include bog plants, fen plants, water, peat and nutrients, are defined based on data from an earlier study of vegetation in the Rothenthurm area in Switzerland, and from published sources.The model is tested for its performance on three types of slope, starting development at a hypothetical state with low amounts of all variables. The development of bogs is traced until a stable state is reached at equilibrium.It is evident from the results that the establishment of a mature stable system takes longest on the flat slope. On all three slopes the peat layer reaches its maximum value before the equilibrium is reached at a slightly reduced peat level. As were observed in the fied, most slope types do not allow a peat bog to persist long under the local climatical conditions, but changes are forced in the vegetation toward a fen type with higher nutrient supply. It was however possible to simulate a stable peat bog when the slope was flat enough (type C in main text). The results of simulation reproduced with reasonable accuracy the shape of the bogs investigated in the field, the abundance of bog and fen plant species, the ground water table, the thickness of peat and the state of nutrient concentrations in the site. The model is rendered to have minimum complexity by assumptions, described in the main text, to reproduce only those properties of peat bogs that were considered primary in importance in the field. The extent to which the model can help to better understand the natural system is discussed.A version of the model described in this paper was developed by the author at the Institute of Geobotany, Swiss Federal School of Technology, Zürich, in 1975–1976. The author expresses his thanks to Prof. Dr. E. Landolt, Director of the Department.