Showing papers by "University of Calgary published in 1993"
TL;DR: A synthesis of laboratory studies and geophysical and geological observations shows that transitions between diffusion and dislocation creep likely occur in the Earth's upper mantle.
Abstract: Rheological properties of the upper mantle of the Earth play an important role in the dynamics of the lithosphere and asthenosphere. However, such fundamental issues as the dominant mechanisms of flow have not been well resolved. A synthesis of laboratory studies and geophysical and geological observations shows that transitions between diffusion and dislocation creep likely occur in the Earth's upper mantle. The hot and shallow upper mantle flows by dislocation creep, whereas cold and shallow or deep upper mantle may flow by diffusion creep. When the stress increases, grain size is reduced and the upper mantle near the transition between these two regimes is weakened. Consequently, deformation is localized and the upper mantle is decoupled mechanically near these depths.
1,627 citations
Book•
30 Aug 1993
TL;DR: Part 1 Systems: Pygmalion tinker a predictive calculator rehearsal world smallStar peridot metamouse TELS eager garnet the Turvy experience chimera the geometer's sketchpad tourmaline a history-based macro by example system mondrian triggers the AIDE project.
Abstract: Part 1 Systems: Pygmalion tinker a predictive calculator rehearsal world smallStar peridot metamouse TELS eager garnet the Turvy experience chimera the geometer's sketchpad tourmaline a history-based macro by example system mondrian triggers the AIDE project. Part 2 Components: a history of editable graphical histories graphical representation and feedback in a PBD system PBD invocation techniques a system-wide macro facility based on aggregate events making programming accessible to visual problem solvers using voice input to disambiguate intent. Part 3 Perspectives: characterizing PBD systems demonstrational interfaces just-in-time programming.
1,083 citations
TL;DR: A set of vector plasmids which greatly facilitate gene replacement and reverse genetics in many Gram-negative bacteria was constructed and it is demonstrated that they are extremely useful in eliminating long and tedious screening procedures.
998 citations
TL;DR: In this article, the authors examined whether differences in the structure of the board of directors and equity ownership contribute to the incidence of hostile takeovers and found that outside directors in hostile targets have lower ownership stakes and hold fewer additional outside directorships.
955 citations
TL;DR: The hypothesis that sequential actions of growth factors play a role in regulating the generation of neurons and astrocytes in the developing CNS is supported.
697 citations
TL;DR: This review addressed in this review on cardiac pacemaking in the sinoatrial node topics are isolated pacemaker cells, membrane currents of sino atrial node cells, mechanism of pacemmaking, and regulation of pacemaker currents.
Abstract: Major topics addressed in this review on cardiac pacemaking in the sinoatrial node are; 1) isolated pacemaker cells; 2) membrane currents of sinoatrial node cells; 3) mechanism of pacemaking; 4) regulation of pacemaker currents
679 citations
TL;DR: The results suggest that the infant central nervous system does not contain programs that detail hand trajectory, joint coordination, and muscle activation patterns, and these patterns are the consequences of the natural dynamics of the system and the active exploration of the match between those dynamics and the task.
Abstract: The onset of directed reaching demarks the emergence of a qualitatively new skill. In this study we asked how intentional reaching arises from infants' ongoing, intrinsic movement dynamics, and how first reaches become successively adapted to the task. We observed 4 infants weekly in a standard reaching task and identified the week of first arm-extended reach, and the 2 weeks before and after onset. The infants first reached at ages ranging from 12 to 22 weeks, and they used different strategies to get the toy. 2 infants, whose spontaneous movements were large and vigorous, damped down their fast, forceful movements. The 2 quieter infants generated faster and more energetic movements to lift their arms. The infants modulated reaches in task-appropriate ways in the weeks following onset. Reaching emerges when infants can intentionally adjust the force and compliance of the arm, often using muscle coactivation. These results suggest that the infant central nervous system does not contain programs that detail hand trajectory, joint coordination, and muscle activation patterns. Rather, these patterns are the consequences of the natural dynamics of the system and the active exploration of the match between those dynamics and the task.
597 citations
TL;DR: Ulastructural colonization and biofilm formation was universal and quantitatively independent of clinical catheter-related infections and luminal in long-term CVC (> 30 days).
Abstract: To assess the degree of luminal and extraluminal colonization of long-term central venous catheters (CVC), 359 indwelling silicone CVC from 340 consecutive cancer patients were examined. All CVC were cultured by the roll-plate and sonication quantitative culture techniques. Semiquantitative electron microscopy was done on 39 CVC associated with catheter infections and on 26 culture-negative controls. An additional 10 culture-negative CVC obtained after death were also studied by electron microscopy. Ultrastructural colonization and biofilm formation was universal and quantitatively independent of clinical catheter-related infections. Ultrastructural colonization and biofilm formation was predominantly luminal in long-term CVC (> 30 days). Based on a composite definition, the sensitivity of the roll-plate catheter tip culture was 42%-45% compared with 65%-72% for the sonication of the tip. Colonization of indwelling catheters is universal regardless of culture results. For long-term CVC, colonization becomes predominantly luminal and extraluminal quantitative catheter cultures are of limited diagnostic sensitivity.
523 citations
TL;DR: The WIND imaging interferometer (WINDII) was launched on the Upper Atmosphere Research Satellite (UARS) on September 12, 1991 and measured wind, temperature, and emission rate over the altitude range 80 to 300 km by using the visible region airglow emission from these altitudes as a target and employing optical Doppler interferometry as discussed by the authors.
Abstract: The WIND imaging interferometer (WINDII) was launched on the Upper Atmosphere Research Satellite (UARS) on September 12, 1991. This joint project, sponsored by the Canadian Space Agency and the French Centre National d'Etudes Spatiales, in collaboration with NASA, has the responsibility of measuring the global wind pattern at the top of the altitude range covered by UARS. WINDII measures wind, temperature, and emission rate over the altitude range 80 to 300 km by using the visible region airglow emission from these altitudes as a target and employing optical Doppler interferometry to measure the small wavelength shifts of the narrow atomic and molecular airglow emission lines induced by the bulk velocity of the atmosphere carrying the emitting species. The instrument used is an all-glass field-widened achromatically and thermally compensated phase-stepping Michelson interferometer, along with a bare CCD detector that images the airglow limb through the interferometer. A sequence of phase-stepped images is processed to derive the wind velocity for two orthogonal view directions, yielding the vector horizontal wind. The process of data analysis, including the inversion of apparent quantities to vertical profiles, is described.
450 citations
TL;DR: The two most commonly used sets of body fixed axes are compared and the differences between them quantified and are shown to be relevant in terms of practical applications of the JCS.
Abstract: The selection of an appropriate and/or standardized method for representing 3-D joint attitude and motion is a topic of popular debate in the field of biomechanics. The joint coordinate system (JCS) is one method that has seen considerable use in the literature. The JCS consists of an axis fixed in the proximal segment, an axis fixed in the distal segment, and a "floating" axis. There has not been general agreement in the literature on how to select the body fixed axes of the JCS. The purpose of this paper is to propose a single definition of the body fixed axes of the JCS. The two most commonly used sets of body fixed axes are compared and the differences between them quantified. These differences are shown to be relevant in terms of practical applications of the JCS. Argumentation is provided to support a proposal for a standardized selection of body fixed axes of the JCS consisting of the axis e1 embedded in the proximal segment and chosen to represent flexion-extension, the "floating" axis e2 chosen to represent ad-abduction, and the axis e3 embedded in the distal segment and chosen to represent axial rotation of that segment. The algorithms for the JCS are then documented using generalized terminology.
448 citations
TL;DR: It is demonstrated that the small reduction in the incidence of venous thrombosis with low-molecular-weight heparin, as compared with warfarin, was offset by an increase in bleeding complications.
Abstract: Background Deep-vein thrombosis is a potentially life-threatening complication of total hip or knee replacement. There are few data on the effectiveness and safety of warfarin as compared with low-molecular-weight heparin as prophylaxis against this problem. Methods We therefore performed a randomized, double-blind trial in 1436 patients to evaluate the effectiveness and safety of low-molecular-weight heparin (given subcutaneously once daily) as compared with adjusted-dose warfarin to prevent venous thrombosis after hip or knee replacement. Treatment with the drugs was started postoperatively. The primary end point was deep-vein thrombosis as detected by contrast venography (performed a mean of 9.4 days after surgery in each group). Results Among the 1207 patients with interpretable venograms, 231 of 617 patients (37.4 percent) in the warfarin group and 185 of 590 patients (31.4 percent) in the low-molecular-weight-heparin group had deep-vein thrombosis (P = 0.03). The reduction in risk with low-molecular...
Journal Article•
Journal Article•
TL;DR: All lines of action and moment arms of the structures of interest were determined as a function of knee joint angles and were expressed using polynomial regression equations to allow easy application of the findings to musculoskeletal models of the human knee joint.
Abstract: The purpose of this study was to obtain lines of action and moment arms in the sagittal plane of the major force-carrying structures crossing the knee joint. The muscles and ligaments studied were the quadriceps, biceps femoris, semimembranosus, and semitendinosus muscles and the anterior and posterior cruciate and medial and lateral collateral ligaments. All lines of action and moment arms of the structures of interest were determined as a function of knee joint angles and were expressed using polynomial regression equations. This representation of the results allows for easy application of the findings to musculoskeletal models of the human knee joint.
TL;DR: In this article, the authors show that large U.S. manufacturing companies with better reputations for social responsibility outperformed companies with poorer reputations during the six-year period 1982-1987, and provided investors better stock market returns and lower risk.
Abstract: During the 1980s there was a rapid growth in the United States of ethical, or socially responsible, investing Popular wisdom suggests that investors following this strategy may be trading off economic returns for psychic utility. However, in this paper we show that large U.S. manufacturing companies with better reputations for social responsibility outperformed companies with poorer reputations during the six-year period 1982–1987, and provided investors better stock market returns and lower risk. The implications of these findings for the information content of accounting systems in a social welfare context, and for prescriptions in the business policy literature advocating a proactive social policy, are discussed.
TL;DR: The observation that both SOD and SIN 1 inhibit leukocyte adhesion only under conditions associated with superoxide formation strongly suggests that the antiadhesion properties of NO are related to its ability to inactivate the superoxide anion.
Abstract: The objective of this study was to determine whether the antiadhesive effects of NO for leukocytes are related to its ability to scavenge superoxide in vivo. Intravital microscopy was used to monit...
TL;DR: In this article, a comparative analysis of chlorite geothermometers is presented, showing that no single chlorite analysis performs satisfactorily over the whole range of natural conditions (different temperatures, coexisting assemblages, Fe/(Fe + Mg), fO2, etc.).
Abstract: Chlorite minerals, found in a great variety of rocks and geological environments, display a wide range of chemical compositions and a variety of polytypes, which reflect the physicochemical conditions under which they formed. Of particular importance for studies dealing with ore deposit genesis, metamorphism, hydrotherrnal alteration or diagenesis is the paleotemperature of chlorite crystallization. However, in order to understand the relationship between chlorite composition and formation temperature and hence use chlorite as a geothermometer, one must determine how other parameters influence chlorite composition. These parameters may include fO2 and pH of the solution and Fe/(Fe + Mg) and bulk mineral composition of the host rock. Four approaches to chlorite geothermometry, one structural and three compositional, have been pro- posed in the past: 1) a polytype method based on the (largely qualitative) observation that structural changes in chlorite may be partly temperature-dependent (Hayes, 1970); 2) an empirical calibration between the tetrahedral aluminum occupancy in chlorites and measured temperature in geothermal systems (Cathelineau, 1988), which has subsequently been modified by several workers; 3) a six-component chlorite solid solution model based upon equilibrium between chlorite and an aqueous solution, which uses thermodynamic properties calibrated with data from geothermal and hydrothermal systems (Walshe, 1986); and 4) a theoretical method based on the intersection of chlorite-carbonate reactions and the CO2- H20 miscibility surface in temperature-XCO2 space, which requires that the composition of a coexisting carbonate phase (dolomite, ankerite, Fe-calcite or siderite) be known or estimated (Hutcheon, 1990). These four approaches are reviewed and the different calculation methods for the compositional geother- rnometers are applied to a selection of chlorite analyses from the literature. Results of this comparative exercise indicate that no single chlorite geothermometer performs satisfactorily over the whole range of natural conditions (different temperatures, coexisting assemblages, Fe/(Fe + Mg), fO2, etc.).. Therefore, chlorite geothermometry should b e used with caution and only in combination with alternative methods of estimating paleotemperatures.
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TL;DR: One of the most influential trends in social theory in the late 20th century has been the collapse of the academic division of labor erected in the beginning of the century (Wolf 1982), which conceded the capitalist marketplace to the new science of economics but defended the realms of the "social," hence noneconomic, as the territory of sociology, political science, and anthropology as mentioned in this paper.
Abstract: One of the most influential trends in social theory in the late 20th century has been the collapse of the academic division of labor erected in the beginning of the century (Wolf 1982), which conceded the capitalist marketplace to the new science of economics but defended the realms of the "social," hence noneconomic, as the territory of sociology, political science, and anthropology (Friedland and Robertson 1990; Marcus 1990) Neoclassical economic theory has been extended to the social realms through innovative work in public choice theory, transaction cost analysis, game theory, human capital theory, and the study of rent-seeking (Oberschall and Leifer 1986) All of these apply neoclassical methods to the explanation of social phenomena that are not conventional parts of the market economy From the other direction, sociologists and anthropologists have extended social and cultural analysis to the heartland of the economic empire: capitalist organization and decision making (Granovetter 1990; Hirsch et al 1990; Zukin and DiMaggio 1990) Studying the ways in which capitalist markets, enterprise organizations, and entrepreneurial activity are themselves social and cultural forms that draw their efficiency partly from sociocultural resources is a welcome departure from the strategy utilized by substantivist economic anthropologists Substantivism conceded the adequacy of neoclassical models to market economies, but denied their applicability to nonmarket economies traditionally studied by anthropologists The collapse of the traditional academic division of labor has led to attempts to overcome dichotomies of the economic and the noneconomic by recognizing the calculative dimension in all forms of exchange and the neglected cultural dimension of market exchanges (Appadurai 1986:12-13) One of the most influential efforts to reintegrate social and economic analysis has been Pierre Bourdieu's theoretical project to develop a "general science of the economy of practices" Such a science would recognize market exchange and capi-
TL;DR: The I-Ceu I maps of Salmonella enteritidis, SalmoneLLA paratyphi A, B, C, and Salmoneella typhi were deduced after digesting genomic DNA and I- Ceu I and probing with DNA of S. typhimurium; the data indicated strong conservation of rrn gene number and position and genome sizes up to 4950 kb.
Abstract: Construction of physical maps of genomes by pulsed-field gel electrophoresis requires enzymes which cut the genome into an analyzable number of fragments; most produce too many fragments. The enzyme I-Ceu I, encoded by a mobile intron in the chloroplast 23S ribosomal RNA (rrl) gene of Chlamydomonas eugametos, cuts a 26-bp site in the rrl gene. This enzyme digests DNA of Salmonella typhimurium at seven sites, each corresponding to one of the rrl genes of the rrn operons, but at no other site. These seven fragments were located on the previously determined Xba I physical map, and the I-Ceu I sites, and thus the rrn genes of S. typhimurium, were mapped on the 4800-kb chromosome. Escherichia coli K-12 also yields seven fragments of sizes similar to those of S. typhimurium, indicating conservation of rrn genes and their location, and a chromosome size of 4600 kb. The sizes of the E. coli fragments are close to the size predicted from restriction maps and nucleotide sequence. The I-Ceu I maps of Salmonella enteritidis, Salmonella paratyphi A, B, C, and Salmonella typhi were deduced after digesting genomic DNA and I-Ceu I and probing with DNA of S. typhimurium; the data indicated strong conservation of rrn gene number and position and genome sizes up to 4950 kb. Digestion of DNA of other bacteria (species of Haemophilus, Neisseria, Proteus, and Pasteurella) suggested that only rrn genes are cut in all these species. I-Ceu I digestion followed by pulsed-field gel electrophoresis is a powerful tool for determining genome structure and evolution.
TL;DR: The data suggest that inhibition of nitric oxide synthesis results in a superoxide and mast cell‐dependent leukocyte adhesion, which suggests that mast cells become activated in the absence ofNitric oxide production and superoxide contributes to the mast cell activation.
Abstract: Recent work has demonstrated that inhibition of nitric oxide production with various nitric oxide synthesis inhibitors (L-NAME, L-NMMA) initiate leukocyte adhesion to postcapillary venules. The objective of this study was to elucidate the mechanism (or mechanisms) that promote the L-NAME-induced leukocyte response. Intravital microscopy was used to examine 25-40 microns venules in the rat mesentery. Nitric oxide synthesis was inhibited with L-NAME and leukocyte adhesion was observed over the first 60 min. The fourfold increase in leukocyte adhesion was independent of alterations in venular red blood cell velocity. The adhesion was superoxide-mediated inasmuch as superoxide dismutase (SOD) abolished the rise in leukocyte adhesion associated with nitric oxide synthesis inhibition. Ketotifen, a mast cell stabilizer, also abolished the rise in leukocyte adhesion induced by L-NAME. Histology revealed that mast cell degranulation occurred only in animals treated with L-NAME but not in animals pretreated with SO...
TL;DR: A causal relationship between malignant hyperthermia (MH) and central core disease (CCD) has been found in this paper, with a lod score of 48 at a recombinant fraction of 00 in 16 informative meioses in a 130 member family.
Abstract: Central core disease (CCD) is a morphologically distinct, autosomal dominant myopathy with variable clinical features A close association with malignant hyperthermia (MH) has been identified Since MH and CCD genes have been linked to the skeletal muscle ryanodine receptor (RYR1) gene, cDNA sequence analysis was used to search for a causal RYR1 mutation in a CCD individual The only amino acid substitution found was an Arg2434His mutation, resulting from the substitution of A for G7301 This mutation was linked to CCD with a lod score of 48 at a recombinant fraction of 00 in 16 informative meioses in a 130 member family, suggesting a causal relationship to CCD
TL;DR: Intestinal permeability in relatives was similar to that in the control group, but a subpopulation had abnormally high permeability rates in the absence of clinical evidence for disease, concluding that the original hypothesis is still viable.
TL;DR: The conjugate synthesis, Margosian, homodyne detection, Cuppen and POCS algorithms are evaluated using spatial frequency domain analysis to show their characteristics and where limitations may occur.
Abstract: Partial Fourier reconstruction algorithms exploit the redundancy in magnetic resonance data sets so that half of the data is calculated during image reconstruction rather than acquired. The conjugate synthesis, Margosian, homodyne detection, Cuppen and POCS algorithms are evaluated using spatial frequency domain analysis to show their characteristics and where limitations may occur. The phase correction used in partial Fourier reconstruction is equivalent to a convolution in the frequency domain and the importance of accurately implementing this convolution is demonstrated. New reconstruction approaches, based on passing the partial data through a phase correcting, finite impulse response (FIR), digital filter are suggested. These FIR and MoFIR algorithms have a speed near that of the Margosian and homodyne detection reconstructions, but with a lower error; close to that of the Cuppen/POCS iterative approaches. Quantitative analysis of the partial Fourier algorithms, tested with three phase estimation techniques, are provided by comparing artificial and clinical data reconstructed using full and partial Fourier techniques.
01 May 1993
TL;DR: In conducting this rather complex simulation, the Wizard of Oz was used to flesh out a design and observe users' reactions as they taught several editing tasks, finding that all users invent a similar set of commands to teach the agent.
Abstract: Turvy is a simulated prototype of an instructible agent. The user teaches it by demonstrating actions and pointing at or talking about relevant data. We formalized our assumptions about what could be implemented, then used the Wizard of Oz to flesh out a design and observe users' reactions as they taught several editing tasks. We found: a) all users invent a similar set of commands to teach the agent; b) users learn the agent's language by copying its speech; c) users teach simple tasks with ease and complex ones with reasonable effort; and d) agents cannot expect users to point to or identify critical features without prompting. In conducting this rather complex simulation, we learned some lessons about using the Wizard of Oz to prototype intelligent agents: a) design of the simulation benefits greatly from prior implementation experience; b) the agent's behavior and dialog capabilities must be based on formal models; c) studies of verbal discourse lead directly to an implementable system; d) the designer benefits greatly by becoming the Wizard; and e) qualitative data is more valuable for answering global concerns, while quantitative data validates accounts and answers fine-grained questions.
TL;DR: Analysis of tau protein isolated from Alzheimer's paired helical filaments and phosphopeptides isolated from the tryptic digest of the phosphorylated bovine tau suggests that BPDK may be one of the kinases responsible for the abnormal phosphorylation-associated PHF-tau.
TL;DR: The hypothesis of a multifactorial etiology for PD, probably involving genetic, environmental, trauma, and possibly other factors, is supported.
Abstract: We studied the relative etiologic importance upon the development of Parkinson9s disease (PD) of occupational exposure to herbicides and other compounds, ionizing radiation exposure, family history of PD and essential tremor, smoking, and history of various viral and other medical conditions. We identified patients (n = 130) with neurologist-confirmed idiopathic PD through contacts with Calgary general hospitals, long-term care facilities, neurologists, the Movement Disorder Clinic, and the Parkinson9s Society of Southern Alberta, and selected two matched (by sex and age ± 2.5 years) community controls for each case by random digit dialing. We obtained lifetime work, chemical, radiation, medical, and smoking exposure histories and family histories of PD and essential tremor by personal interviews, and analyzed the data using conditional logistic regression for matched sets. After controlling for potential confounding and interaction between the exposure variables, using multivariate statistical methods, having a family history of PD was the strongest predictor of PD risk, followed by head trauma and then occupational herbicide use. Cases and controls did not differ in their previous exposures to smoking or ionizing radiation; family history of essential tremor; work-related contact with aluminum, carbon monoxide, cyanide, manganese, mercury, or mineral oils; or history of arteriosclerosis, chicken pox, encephalitis, hypertension, hypotension, measles, mumps, rubella, or Spanish flu. These results support the hypothesis of a multifactorial etiology for PD, probably involving genetic, environmental, trauma, and possibly other factors.
TL;DR: It is concluded that perfused rat mesenteric arterial bed releases both EDHF and EDNO in response to ACh and histamine, and EDHF plays a dominant role in maintenance of the basal perfusion pressure in this vascular bed, and both ED HF andEDNO relaxations are mediated by activation of M3 muscarinic cholinoceptors.
Abstract: We describe a simple, functional approach to defining the relative contribution of endothelium-dependent hyperpolarization (presumably mediated by a factor, EDHF) and endothelium-derived nitric oxide (EDNO) to acetylcholine (ACh) and histamine relaxations of isolated perfused rat mesenteric resistance arterial bed. In physiologic salt solution (PSS), ACh- and histamine-induced vasodilations of cirazoline-preconstricted mesenteric arterial bed were only partially attenuated by 50 microM Nw-nitro-L-arginine methyl ester (L-NAME). The L-NAME-resistant component was abolished by 0.5 microM apamin but not by 250 nM dendrotoxin or 10 microM glyburide, thus indicating a role for apamin-sensitive K+ channels in mediating the effects of the putative EDHF. Changing membrane potential by varying [K+] decreased L-NAME-resistant vasodilation, and showed a modest L-NAME-induced increase in the basal perfusion pressure that was not observable in normal PSS. Vasodilator responses during cirazoline-induced tonus in 20 mM K+ and normal PSS were superimposable, but responses to ACh and histamine in 20 mM K+ were profoundly more sensitive to L-NAME than were those in normal PSS media. ACh responses during 20-mM K+ PSS perfusion and presumably mediated by EDNO and those resistant to L-NAME and putatively mediated by EDHF were antagonized by graded concentrations of p-fluorohexahydro-siladifenidol (p-F-HHSiD), but not pirenzepine.(ABSTRACT TRUNCATED AT 250 WORDS)
TL;DR: Two different TIMPS have been well characterized, each capable of inhibiting all tested eukaryotic metalloproteinases but showing specific binding to a particular gelatinase at a site distinct from the active site.
TL;DR: Although the suspensor appears to play a critical role in zygotic embryogenesis, it usually fails to develop when somatic embryos are produced in culture and should be viewed as a specialized structure that functions primarily to facilitate continued development of the embryo proper within the seed.
Abstract: The zygote in flowering plants usually divides transversely to form a terminal cell, which gives rise to the embryo proper, and a vacuolated basal cell, which often divides rapidly to form a structure known as the suspensor. Angiosperm suspensors vary widely in size and morphology from a single cell to a massive column of several hundred cells (Maheshwari, 1950; Wardlaw, 1955; Lersten, 1983). In most cases, the suspensor functions early in embryogenesis and then degenerates during later stages of development and is not present in the mature seed. Classically, the suspensor was thought to play a passive role in embryo development by holding the embryo proper in a fixed position within the seed (Maheshwari, 1950). It now appears from extensive structural, biochemical, and physiological studies with a variety of angiosperms that the suspensor plays an active role early in development by promoting continued growth of the embryo proper. In addition, growth of the suspensor during early stages of development may be inhibited by the embryo proper (Marsden and Meinke, 1985). Analysis of reproductive development in angiosperms must therefore include a consideration of developmental interactions that occur between the embryo proper and suspensor. Although the suspensor appears to play a critical role in zygotic embryogenesis, it usually fails to develop when somatic embryos are produced in culture. The suspensor should therefore be viewed as a specialized structure that functions primarily to facilitate continued development of the embryo proper within the seed. In this review, we present an overview of the structure and function of the angiosperm suspensor and discuss recent attempts to analyze the development of the suspensor through a combination of descriptive, experimental, and genetic approaches. The recent identification of a large collection of Arabidopsis mutants with abnormal suspensors provides a unique opportunity to examine the underlying genetic factors that influence suspensor development.