Optic nerve responses to visual stimuli in squid

Summary Single unit optic nerve responses were studied in isolated eye-optic lobe preparations ofLoligo opalescens. Units could be classified as fast or slow. Fast units were invariably receptor cell axons; slow units might be either receptor cell axons or centrifugal axons.On, on-off, andoff units could be found within these classes. A given unit was not stable with respect to these latter attributes which depended greatly on the history and level of illumination. The curve which relates quantal content of a brief flash to number of spikes in the response has a logarithmic phase, but it saturates as brightness is increased further. An inhibitory component has been demonstrated following the response to a flash. It is probably responsible for the non-monotonic relationship between frequency and light intensity which is observed for sustained stimuli. Background light or previous illumination can lead to a facilitation of the response to a flash.The authors share equally in credit and responsibility for this paper and for the research reported here. We thank Dr. A. Hurley and Dr. T. H. Bullock for valuable comments and suggestions and L. Ball and S. St. John for technical assistance. This research was supported by PHS grants NS 09342 to GDL and EY 29405 to PHH, by a grant from the Sloan Foundation to the group in Neurosciences at UCSD and NSF grants GB 24816 and GD 28838 to the Scripps Institution of Oceanography for operation of the Alpha Helix Research Program.     

Model membranes: Spherical shells bounded by one bimolecular layer of phospholipids

Summary The conditions are described which lead to the formation of small spherical vesicles bounded by singlelipid membranes. These membranes appear as triple-layered structures in electron micrographs and thus resemble theunit membrane configuration of cellular boundaries. The theory of light scattering by spherical shells is found applicable to the vesicles described here; size determinations by electron microscopy (r=195 Å) and by light scattering (r=225 Å) give reasonably close values. The refractive index of the membranes as determined by differential refractometry is found to be 1.46 for green incident light of wavelength 5461 Å.The results of this work were presented in part at the Symposium on Biophysical Aspects of Permeability, Jerusalem, Israel, July 2–9, 1968.I gratefully acknowledge the help provided me during this work by Dr Walter Stoeckenius, and I also thank Dr Dominic Dziewiatkowski for the permission to use his light scattering photometer.This work was supported by grant No. GB-4871 from the National Science Foundation.     

Modification of a stimulus-reinforcer interaction by blocking

With tone-light compound-stimulus training, light will gain control of responding under an appetitive schedule while tone will gain considerable control with avoidance training. The present experiment sought to determine whether this stimulus-reinforcer interaction could be modified by a “blocking” procedure. Initially, one group of rats was trained to respond for food in tone while tone-off was food free, and a second group was trained to avoid shock in light while light-out was shock free. Following attainment of a 10:1 discrimination ratio, food and avoidance schedules were signaled, for the respective groups, by a tone-light compound stimulus. An element test demonstrated that the blocking procedure overcame the stimulus-reinforcer interaction previously reported with rats in both the appetitive and avoidance groups. Contrary to previous stimulus-reinforcer interaction research, here, the tone, rather than the light, controlled responding after food training while the light, rather than the tone, controlled responding after avoidance training. These results obey predictions from associative theory. The current experiment is also the first demonstration of blocking within an instrumental avoidance procedure.     

LD ratios and the entrainment of circadian activity in a nocturnal and a diurnal rodent

Summary The activity rhythms of 5 flying squirrels,Glaucomys volans, and 7 chipmunks,Tamias striatus, were examined under controlled conditions in the laboratory. Free-running, circadian rhythms were demonstrated using a total of 25 LL or DD experiments. With 46 LD schedules the limits of entrainment in a 24-hour day were determined, and the phase angle difference for each schedule measured.Glaucomys was able to synchronize to schedules ranging from 1 second of light per 24-hour day to at least 18 hours light per day with little or no change in the phase angle.Tamias showed an oscillatory type of entrainment when the photoperiod was less than 3 hours per 24-hour day or greater than 23 hours, but in the intervening region was capable of stable entrainment. A tendency was evident for the phase angle difference to become less positive as the LD ratio increased. InGlaucomys single, isolated light pulses of either one second or 24 hours duration were able to bring about relatively large shifts in the phase of the activity rhythm.Dedicated to Professor Jürgen Aschoff on the occasion of his 60th birthday.I wish to acknowledge the hospitality and assistance of the Zoology Department, University of Wisconsin, Madison, the Max-Planck Institute, Erling-Andechs, Germany, and the Belle W. Baruch Coastal Research Institute, University of South Carolina, Columbia. Special thanks are due Dr. John Emlen and Dr. William Reeder of Madison, Prof. J. Aschoff of Erling-Andechs, Dr. John Vernberg and Dr. Winona Vernberg of Columbia, and my husband, Dr. George DeCoursey, for their untiring encouragement and help with these experiments.     

Influence of light and darkness on the hypothalamo-hypophysial system of Rana temporaria L.

Summary The influence of a long daily photoperiod and continuous darkness was studied on the hypothalamo-hypophysial system of Rana temporaria. After six weeks of treatment (December-January 1968/1969) the secretory activity of the hypothalamo-hypophysial system of the light-treated animals was enhanced.The amount of aldehyde-fuchsin positive material in the preoptic nucleus increased as a result of the light treatment, and decreased in the median eminence, whereas in the posterior lobe no difference could be observed between the light- and dark-treated animals.The karyometric results showed an increase of the nuclear volume of the cells of the preoptic nucleus after light treatment; small differences were noticed between distinct areas of the preoptic nucleus.Autoradiographic data especially showed that light influenced the hypothalamo-hypophysial system to a high degree. Half an hour after the injection of ³⁵S-cysteine, the incorporation of the isotope in the preoptic nucleus of the light-treated animals was five times as much as in the dark-treated animals. In the median eminence and in the posterior lobe, the autoradiographic results confirmed the results found with regard to the amount of aldehyde-fuchsin positive material. Labelled material is released only from the median eminence and not from the posterior lobe.The author is indebted to Prof. Dr. J. C. van de Kamer and Dr. F. C. G. van de Veerdonk for their interest and helpful encouragement. Thanks are also due to Ir. J. J. Bezem for his assistance in solving the statistical problems and to Mr. H. van Kooten and his staff for making the illustrations. The co-operation of the student Mr. E. Schenk is gratefully acknowledged. Dr. L. Boomgaart was so kind to check and amend the English writing.     

The effectiveness of EMG biofeedback training in low back pain

Eighteen patients with chronic low back pain(lbp) of muscle tension origin were given an EMG biofeedback training. Compared to seven controls they showed a significant decrease during training in muscle tension and subsequently in pain. However, at follow-up EMG levels dropped to the initial(high) level. Pain scores of patients with high pain decrements during training showed further improvement during follow-up, which was not the case with patients showing less substantial improvement. The importance of cognitions was discussed.We wish to express our thanks to Marijke Höweler-van Dalen for supervising this investigation, to Arnold Goedhart for statistical advice, to Dr. Orlebeke for his critical remarks, and to Dr. Penders for referring the patients in Amsterdam. We are particularly indebted to the general practitioners Paul Kreutzer and Jan Huls for referring the Andijk patients. Without their support this investigation would not have been possible.     

An in situ study of the preoptico-neurohypophysial complex of the freshwater teleost Ciarias batrachus (L.)

Summary The complicated architectural pattern of the preoptico-neurohypophysial neurosecretory system of Clarias batrachus is described using bulk staining procedure. The nucleus preopticus is U-shaped; its limbs constitute the PMC and PPC. The difference in staining intensities noticed among the PMC and PPC might suggest a possible functional difference within the system. Axons of the PMC diagonally pass through the PPC and emerge along with those of the latter to form the right and the left main tracts. The folds and recurrent curves of the neurosecretory axonal tracts, the formation of several pairs of lateral tracts and their union to form median tracts might be devices to increase the storing and releasing capacity for the neurosecretory material. The presence of prominent Herring bodies, and diffuse areas in the neurosecretory tract suggest possible sites of release of neurohormones along the highly vascular hypothalamic region. The common neurosecretory tract is divided into several smaller branches at the level of the pars distalis prior to entering the pars intermedia. Branches do penetrate into the pars distalis, but those entering the rostral component of the pituitary are relatively scarce.Regeneration of the anterior stump of the severed hypophysial stalk to form a neurohypophysis-like organ is also demonstrated in toto with the aid of the bulk staining procedure. A demonstrable increase of stainable neurosecretory material was noticed all along the hypothalamo-neurohypophysial complex of some specimens subjected to complete darkness. Total staining methods could be advantageously used to map the course of recurrent tracts and extra-hypophysial axonal endings. Since the neurosecretory system seems to exhibit a varied structural pattern in different fishes, extension of this study to a larger number of species may throw additional light on the function and the evolution of this important system.I am indebted to Dr. K. N. Udupa, Principal, College of Medical Sciences and Director, Surgical Research Laboratory and Dr. L. M. Singh, Officer in-charge of the Laboratory for providing all facilities and encouragements.     

Microbodies (peroxisomes) in the toad,Bufo marinus

Summary Microbodies (peroxisomes), a group of cytoplasmic organelles enriched in catalase, are demonstrated in the toad, Bufo marinus, by light and electron microscopy by means of a cytochemical staining procedure that demonstrates the peroxidatic activity of catalase with diaminobenzidine (DAB). Amphibian microbodies are similar to those of other classes in their fine structure and localization in hepatocytes and kidney, where they are prominent in the proximal tubular cells. Nucleoids are present only in renal microbodies. In the proximal renal tubule an unusual group of large brown granules are identified as lysosomes by their acid phosphatase, -glucosaminidase and -glucuronidase activities.This work was supported by U.S. Public Health Service Grants Nos. NS-06856 and HD 00674. We wish to thank Dr. Richard M. Hays who generously supplied us with toads; Dr. Alex B. Novikoff for making available facilities for ultramicrotomy, Miss Betty De Prest for technical assistance; Miss Marianne Van Hooren for preparation of the photomicrographs.     

Biofeedback,relaxation training,and music: Homeostasis for coping with stress

This study compared the efficacy of five relaxation training procedures, four of which employed EMG auditory feedback: (1) biofeedback only (BF), (2) autogenic training phrases (ATP), (3) music (MU), (4) autogenic training phrases and music (ATP & MU), and (5) a control group, in developing self-regulation of a cultivated low arousal state as a countermeasure to tensed muscular reaction to stressful imagery. Twenty subjects established a pre- and posttraining frontalis region EMG biofeedback baseline measurement. Sixteen subjects were assigned at random to the 25-minute taped relaxation training procedure. After eight training sessions (4 weeks), MU and ATP & MU groups achieved highly significant differences when compared with the control group. The ATP & MU group attained the lowest postbaseline arousal level measured by the EMG. EMG as a physiological measure for transfer of training functioned well in detecting the psychophysiological affect of stressful imagery.This report is based on a thesis submitted in partial fulfillment of the requirements for the Master of Arts in Psychology degree by the author. The author extends his gratitude to Dr. Theodore Steiner, Dr. Paul Eskildsen, and Dr. Frank Hovell, who served on the committee, and to Rosemary Kolentus, for her help with this article.     

Phytochrome inhibits the effectiveness of gibberellins to induce cell elongation in rice

Red light controls cell elongation in seedlings of rice (Oryza sativa L.) in a far-red-reversible manner (Nick and Furuya, 1993, Plant Growth Regul. 12, 195–206). The role of gibberellins and microtubules in the transduction of this response was investigated in the rice cultivars Nihon Masari (japonica type) and Kasarath (indica type). The dose dependence of mesocotyl elongation on applied gibberellic acid (GA₃) was shifted by red light, and this shift was reversed by far-red light. In contrast, coleoptile elongation was found to be independent of exogenous GA₃. Nevertheless, it was inhibited by red light, and this inhibition was reversed by far-red light. The content of the active gibberellin species GA₁ and GA₄ was estimated by radio-immunoassay. In the mesocotyl, the gibberellin content per cell was found to increase after irradiation with red light, and this increase was far-red reversible. Conversely, the cellular gibberellin content in japonica-type coleoptiles did not exhibit any significant light response. Microtubules reoriented from transverse to longitudinal arrays in response to red light and this reorientation could be reversed by subsequent far-red light in both the coleoptile and the mesocotyl. This movement was accompanied by changes in cell-wall birefringence, indicating parallel reorientations of cellulose deposition. The data indicate that phytochrome regulates the sensitivity of the tissue towards gibberellins, that gibberellin synthesis is controlled in a negative-feedback loop dependent on gibberellin effectiveness, and that at least two hormone-triggered signal chains are linked to the cytoskeleton in rice.Abbreviations D darkness - FR far-red light - GA₃ gibberellic acid - GC-SIM gas chromatography-selected ion monitoring - R red light This work was supported by a grant of the Human Frontier Science Organization to P.N. Advice and organizational support by Prof. M. Furuya (Hitachi Advanced Research Laboratory, Hatoyama, Japan) and Prof. N. Murofushi (Department of Agricultural Chemistry, University of Tokyo, Japan) is gratefully acknowledged. Seeds of both rice cultivars were kindly provided by Dr. O. Yatou (Institute for Radiation Breeding, Hitachi-Ohmiya, Japan), and the antiGA₁ Me-antiserum for the radio-immunoassays by Dr. I. Yamaguchi (Department of Agricultural Chemistry, University of Tokyo, Japan).     

Alpha brainwave training and perception of time passing: Preliminary findings

The ability to generate alpha brainwaves has been associated with the self-regulation of stress. It has been suggested that generation of these brainwaves, above what is to be expected in a normal 24-hour EEG, contributes to an expanded state of consciousness. This study attempted to test Newman's theory that expansion of consciousness could be observed in perception of time passing. Twenty female college students were randomly assigned to an alpha brainwave training or beta (mock) brainwave training group. Following ten 30-minute training sessions over a five-week period of time, each subject in each group was asked to produce ten randomly assigned time intervals. Mean scores were obtained for each of the ten intervals for each group. An analysis of variance with repeated measures was used to analyze the time interval perceptions of each group. According to results obtained, both main effects and interaction effects were highly significant (p<.0001). This study offers a beginning effort to examine the consciousness altering capability of alpha brain-wave generation.The author wishes to acknowledge Dr. Alton J. DeLong for his generosity in reviewing this paper and offering such helpful support and suggestions.     

Light and Branch Formation in the Alga Vaucheria dichotoma (Xanthophyceae)

Branches of Vaucheria dichotoma (L.) Ag. were induced in two ways: by cutting, which led to a branch in the wound area and by exposure to light. Blue and red light were most active in branch formation. The light intensity dependence and the action spectrum of branch formation showed patterns similar to those of photosynthesis. Photosynthetic involvement was also indicated by the DCMU inhibition of branch formation. Elongation-branching studies at different photoperiods showed that branching was increased by the presence of more photosynthetic light than was necessary for elongation. It may be concluded that photosynthesis exerted the main control of the branch formation of V. dichotoma. However, the action spectrum of branch formation showed a higher efficiency in blue light than would be expected from the action spectrum of photosynthesis. It is therefore possible that apart from the main induction via the photosynthetic pigments, other blue light sensitive pigments may have a regulatory effect. Far-red light treatment of filaments pre-exposed to 8-h and 16-h light periods did not affect branch formation. Spectrophotometrical detection of phytochrome was not successful. This may indicate that there is no participation of phytochrome in branch formation. I am indebted to Dr. Lisbeth Fries for her interest. I also wish to thank Prof. Lars Olof Björn and his friendly staff at the Institute of Plant Physiology at the University of Lund, where some of the experiments were carried out. I am grateful to AB Tomaso Minori for revising the English test and to Miss Inga-Britt Jansson for typing it. The investigation was supported financially by a grant to Dr. Lisbeth Fries from the Swedish National Science Research Council.     

Functional xylem anatomy in root-shoot junctions of six cereal species

In cereals, the formation of safety zones in the root-shoot junction could protect the vessels of roots from embolism originating in the shoot. The root-shoot junction was examined both anatomically, with a light microscope, and experimentally, using a pressurized-air method, in the base of seminal and adventitious roots of maize (Zea mays L. cv. Seneca 60-II), a corngrass mutation of maize (Cg mutant), sorghum (Sorghum bicolor L. cv. Ho-Pak), winter oats (Avena sativa L. cv. Ogle), spring wheat (Triticum aestivum L. cv. Glenlea), winter wheat (T. aestivum cv. Monopol), winter barley (Hordeum vulgare L. cv. Wysor), spring rye (Secale cereale L. cv. JO-02 Finland), and winter rye (S. cereale cv. Musketeer). Two types of hydraulic architecture were found in the cereal roots: (i) a very safe root vessel system, as in winter rye, in which the vessels of the roots are separated from those of the shoots by tracheids, versus (ii) a completely unsafe system, as in corngrass, where the vessels in the root are continuous with the vessels in the shoot. The xylem anatomy of the seminal roots is generally correlated with the species-specific overall root morphology. Rye, wheat and barley, which develop four to six seminal roots, show a high degree of vascular segmentation resulting in, the formation of safe root vessels; maize, sorghum and oats, which typically develop a primary seminal root, contain unsafe vessels that are continuous through the mesocotyl and through the first node. In adventitious roots, vascular segmentation is not related to overall root morphology. Differences in the proportion of safe adventitious roots in which all the vessels end in the root-shoot junction range from 9 to 98% in the cereals studied. In the unsafe roots of these cereals, the number of vessels per root that are continuous through the junction range from 1 to 14. As significant differences in vascular segmentation of the root-shoot junction occur not only between species, but also between cultivars, we suggest that selection based on the occurrence of safety zones might be used in breeding programs designed to improve adaptation of cereals to drought and cold temperatures.This research project was supported by the Natural Sciences and Engineering Research Council of Canada through an International Scientific Exchange Award to R.A. and Dr. C.A. Peterson, and through an Operating Grant to M.G. We thank Dr. G. McLeod (Agriculture Canada, Swift Current, Sask., Canada), Dr. N.P.A. Huner (University of Western Ontario, London, Ont., Canada) and Dr. W.F. Tracy (University of Wisconsin, Madison, USA) for providing seeds; Dr. C.A. Peterson and Dr. W.B. McKendrick (University of Waterloo) for use of the Zeiss photomicroscopes; Dr. M.A. Dixon (University of Guelph, Guelph, Ont.) for use of the Moore pressure gauge; and Dr. R.J. O'Hara-Hines (University of Waterloo) for statistical advice.     

The DraC usher in Dr fimbriae biogenesis of uropathogenic E. coli Dr+ strains

Biogenesis of Dr fimbriae encoded by the dra gene cluster of uropathogenic Escherichia coli strains requires the chaperone-usher pathway. This secretion system is based on two non-structural assembly components, the DraB periplasmic chaperone and DraC outer-membrane usher. The DraB controls the folding of DraE subunits, and DraC forms the assembly and secretion platform for polymerization of subunits in linear fibers. In this study, mutagenesis of the DraC N-terminus was undertaken to select residues critical for Dr fimbriae bioassembly. The DraC-F4A, DraC-C64, DraC-C100A and DraC-W142A significantly reduced the adhesive ability of E. coli strains. The biological activity of the DraC mutants as a assembly platform for Dr fimbriae polymerization was verified by agglutination of human erythrocytes and adhesion to DAF localized at the surface of CHO-DAF⁺ and HeLa cells. The residue F4 of the DraC usher conserved among FGL and FGS chaperone-assembled adhesive organelles can be used to design pillicides blocking the biogenesis of Dr fimbriae. Because the draC and afaC-III genes share 100% identity the range of the virulence determinant inhibitors could also be extended to E. coli strains encoding afa-3 gene cluster. The investigations performed showed that the usher N-terminus plays an important role in biogenesis of complete fiber.     

Studies on initiation and development of the partner association inGeosiphon pyriforme (Kütz.) v. Wettstein,a unique endocytobiotic system of a fungus (Glomales) and the cyanobacteriumNostoc punctiforme (Kütz.) Hariot

Summary Phagocytosis ofNostoc filaments byGeosiphon, a fungus closely related to AM forming Glomales, was observed under light microscopes. Incorporation can only be performed ifNostoc primordia come into contact with growing hyphal tips of the fungus. The fungal wall just below the apex softens, and fungal cytoplasm is bulged out repeatedly covering the vegetativeNostoc cells but not the heterocytes. New heterocytes are differentiated by the internalised filament whose cells can increase up to ten times in volume after recovering from incorporation strain. TheNostoc cells are coated stepwise by short finger-shaped protuberances of the fungal hypha. These hernia-like outgrowths first remain separated, after 1 to 2 days they merge. Adjacent hyphal walls inside the complex covering disintegrate. Periphal fungal wall portions are united to form a smooth strong outer envelope. Internalisation is categorised as phagocytosis. The partnership is partly specific,Nostoc strains capable of living endocytobiotically are often partners in other symbioses besidesGeosiphon.Abbreviations AM arbuscular mycorrhiza (formerly VAM vesicular arbuscular mycorrhiza) - DIC differential interference contrast - LD light/dark Dedicated to Prof. Dr. Dr. h.c. Eberhard Schnepf on the occasion of his retirement     

Electromyographic biofeedback for tension control during fine motor skill acquisition

The presence of residual muscular tension has been implicated as a detrimental influence on the performance and learning of motor skills. A method for reducing muscular tension has been provided by the advent of biofeedback training. This study investigated the effects of tension-control training by electromyographic (EMG) biofeedback on learning and performance of the pursuit-rotor backing task. Thirty young adult males were pretested for pursuit-rotor (PR) tracking skill, ranked by performance scores, and divided into identical triplicates to form two experimental groups and a control group. After a total of 3 hours of EMG biofeedback training for the experimental groups, all subjects were reevaluated on the PR test. One experimental group received biofeedback during the posttests. Analysis of variance of pretest-posttest difference means andt tests of scores representing performance and tension indicated that the EMG biofeedback training (1) significantly reduced tension induced by the novel motor skill and (2) significantly improved performance of the motor skill. Transfer of tension-control training was shown to facilitate learning and performance more than direct EMG biofeedback during performance. Residual tension reduction during learning was particularly facilitated by EMG biofeedback training, a profound implication for the management of stress in a variety of situations.This investigation formed part of a Ph.D. dissertation research (1976) conducted by the author under the guidance of Dr. Donald E. Campbell, Department of Physical Education, and Dr. Carol A. Saslow, Department of Psychology, at Oregon State University.     

Cell interaction at the maternal-embryonic interface during implantation in the mouse

Summary The interaction between the trophoblast and the maternal epithelium at early implantation was studied by means of light and electron microscopy. The uterine horns were fixed in situ and a double-embedding method was used to locate implantation sites. Observations were made on mice killed at 2 hour intervals 90–116 h. post coitum which covered the following stages: pre-attachment (i) with zona pellucida intact (ii) with zona pellucida in dissolution (iii) after loss of the zona; attachment; adherence; and invasion.The intact zona pellucida was electron opaque and of uniform density. In the stage of apparent dissolution it became electron dense and was trapped between trophoblast and epithelium.At preattachment the trophoblast cells were round. Subsequently they became long and attenuated, often with lysosomes in the cytoplasm proximal to the epithelial layer. Epithelial cells, which could be seen in various stages of degeneration were apparently phagocytosed by the trophoblast. Occasional pyknotic epithelial cells were seen, as well as some apparently normal ones which contained cytosegresomes. The possible reasons for their presence are discussed.The microvilli of the epithelial cells changed from regular and pointed at preattachment to short and irregular at adherence and invasion.Research supported by the Lalor Foundation, Wilmington, Del, U.S.A. to I.B.W.We are grateful to Dr. H. M. Beaumont, and Dr. L. L. Franchi of the Anatomy Department, Birmingham, for helpful discussion and to Mr. J. Wallington for photographic assistance.     

Retinal responses in squid and octopus

Summary Electroretinogram and optic nerve impulse recordings from an isolated eye-optic lobe preparation of squid and octopus show: 1) linear and nonlinear responses to modulated light; 2) facilitation of retinal and optic nerve responses to pairs and trains of suitably spaced brief flashes; 3) bothon andoff responses in optic nerve fibers; 4) centrifugally conducted impulses in the optic nerve which may be excited or inhibited by light; and 5) oscillatory behavior which has a stable, temperature dependent frequency. All of these phenomena other than the centrifugal activity can be gotten with isolated eyes. The non-impulse behavior can also be gotten from small pieces of retina. There is therefore evidence for highly complex activity within local areas of the anatomically simple retina.The authors share equally in credit and responsibility for this paper and for the research reported here. We thank Dr. A. Hurley and Dr. T. H. Bullock for valuable comments and suggestions and L. Ball and S. St. John for technical assistance. This research was supported by PHS grants NS 09342 to GDL and EY 29405 to PHH, by a grant from the Sloan Foundation to the group in Neurosciences at UCSD and NSF grants GB 24816 and GD 28838 to the Scripps Institution of Oceanography for operation of the Alpha Helix Research Program.     

Changes in composition of the outer epidermal cell wall of pea stems during auxin-induced growth

The gross composition of the outer epidermal cell wall from third internodes of Pisum sativum L. cv. Alaska grown in dim red light, and the effect of auxin on that composition, was investigated using interference microscopy. Pea outer epidermal walls contain as much cellulose as typical secondary walls, but the proportion of pectin to hemicellulose resembles that found in primary walls. The pectin and hemicellulose fractions from epidermal peels, which are enriched for outer epidermal wall but contain internal tissue as well, are composed of a much higher percentage of glucose and glucose-related sugars than has been found previously for pea primary walls, similar to non-cellulosic carbohydrate fractions of secondary walls. The epidermal outer wall thus has a composition rather like that of secondary walls, while still being capable of elongation. Auxin induces a massive breakdown of hemicellulose in the outer epidermal wall; nearly half the hemicellulose present is lost during 4 h of growth in the absence of exogenous sugar. The percentage breakdown is much greater than has been seen previously for whole pea stems. It has been proposed that a breakdown of xyloglucan could be the basis for the mechanical loosening of the outer wall. This study provides the first evidence that such a breakdown could be occurring in the outer wall.M.S. Bret-Harte would like to thank Dr. Peter M. Ray, of Stanford University, for helpful discussions and for technical and editorial assistance, Dr. Winslow R. Briggs, of the Camegie Institude of Washington, for the use of experimental facilities and for helpful discussions, Dr. Wendy K. Silk, of the University of California, Davis, for helpful discussions and financial support, Dr. Paul B. Green for financial support, and Drs. John M. Labavitch and L.C. Greve, of the University of California, Davis, for performing the -cellulose analysis on short notice, in response to a request by an anonymous reviewer. This work was supported by a National Science Foundation Graduate Fellowship to M.S. B.-H., National Science Foundation Grant DCB8801493 to Paul B. Green, and the generosity of Wendy K. Silk (Department of Land, Air, and Water Resources, University of California, Davis) during the final writing.