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Our understanding of the effects of heat stress on plant photosynthesis has progressed rapidly in recent years through the use of chlorophyll a fluorescence techniques. These methods frequently involve the treatment of leaves for several hours in dark conditions to estimate declines in maximum quantum yield of photsystem II (F V/F M), rarely accounting for the recovery of effective quantum yield (ΔF/F M′) after thermally induced damage occurs. Exposure to high temperature extremes, however, can occur over minutes, rather than hours, and recent studies suggest that light influences damage recovery. Also, the current focus on agriculturally important crops may lead to assumptions about average stress responses and a poor understanding about the variation among species’ thermal tolerance. We present a chlorophyll a fluorescence protocol incorporating subsaturating light to address whether species’ thermal tolerance thresholds (T 50) are related to the ability to recover from short-term heat stress in 41 Australian desert species. We found that damage incurred by 15-min thermal stress events was most strongly negatively correlated with the capacity of species to recover after a stress event of 50 °C in summer. Phylogenetically independent contrast analyses revealed that basal divergences partially explain this relationship. Although T 50 and recovery capacity were positively correlated, the relationship was weaker for species with high T 50 values (>51 °C). Results highlight that, even within a single desert biome, species vary widely in their physiological response to high temperature stress and recovery metrics provide more comprehensive information than damage metrics alone.

The aim of this study is to investigate the significance of nonpolar functional groups in the surface orientation-dependent adsorption of natural and synthetic antifreeze proteins (AFPs) on ice. We investigate using nanoliter osmometry, ice etching, and circular dichroism spectroscopy a series of nine designed α-helical peptides to probe the nature of their selectivity between the bipyramidal {201} and the secondary prismatic {210} faces of ice, identified earlier as the preferred faces for adsorption of winter flounder (WF) and shorthorn sculpin type I AFPs, respectively. Complementarities between the AFP’s surface features, comprised chiefly of nonpolar groups, and the well-defined sites on ice surface, allow close contact. Because our experimental studies demonstrate that the function of AFPs relies on participation of both polar and nonpolar residues in the ice surface adsorption, we carry out computational modeling to explore both kinds of contacts at the ice surface. On the basis of results of semi...

A tillage and straw management study was started near Delta Junction Alaska (64°49′N, 147°52′W) USA in 1983 to determine the impact of tillage, straw management, and nitrogen fertilizer application...

†Background and Aims It has been proposed that having too much DNA may carry physiological consequences for plants. The strong correlation between DNA content, cell size and cell division rate could lead to predictable morphological variation in plants, including a negative relationship with leaf mass per unit area (LMA). In addition, the possible increased demand for resources in species with high DNA content may have downstream effects on maximal metabolic efficiency, including decreased metabolic rates. †Methods Tests were made for genome size-dependent variation in LMA and metabolic rates (mass-based photosynthetic rate and dark respiration rate) using our own measurements and data from a plant functional trait database (Glopnet). These associations were tested using two metrics of genome size: bulk DNA amount (2C DNA) and monoploid genome size (1Cx DNA). The data were analysed using an evolutionary framework that included a regression analysis and independent contrasts using a phylogenetic tree with estimates of molecular diversification times. A contribution index for the LMA data set was also calculated to determine which divergences have the greatest influence on the relationship between genome size and LMA. †Key Results and Conclusions A significant negative association was found between bulk DNA amount and LMA in angiosperms. This was primarily a result of influential divergences that may represent early shifts in growth form. However, divergences in bulk DNA amount were positively associated with divergences in LMA, suggesting that the relationship may be indirect and mediated through other traits directly related to genome size. There was a significant negative association between genome size and metabolic rates that was driven by a basal divergence between angiosperms and gymnosperms; no significant independent contrast results were found. Therefore, it is concluded that genome size-dependent constraints acting on metabolic efficiency may not exist within seed plants.

Little is known about the long-term effects of tillage and crop residue management on soil quality and organic matter conservation in subarctic regions. Therefore, we quantified wet aggregate stability, bulk density, pH, total organic C and N, inorganic N, microbial biomass C and N, microbial biomass C:N ratio, microbial quotient, and potential C and N mineralization for a tillage/crop residue management study in central Alaska. Soil from no-till (NT), disked once each spring (DO), and disked twice (DT, spring and fall) treatments was sampled to 20 cm depth in spring and fall of the 16th and 17th years of the study. Crop residues were either retained or removed after harvest each year. Reducing tillage intensity had greater impact on most soil properties than removing crop residues with the most notable effects in the top 10 cm. Bulk density was the only indicator that showed significant differences for the 10–20 cm depth, with values of 0.74 Mg m −3 in the surface 10 cm in NT compared to 0.86 in DT and 1.22 Mg m −3 in NT compared to 1.31 in DT for the 10–20 cm depth. Wet aggregate stability ranged from 10% in DT to 20% in NT. Use of NT or DO conserved soil organic matter more than DT. Compared to measurements made in the 3rd and 4th years of the study, the DT treatment lost almost 20% of the soil organic matter. Retaining crop residues on the soil conserved about 650 g m −2 greater C than removing all residues each year. Soil microbial biomass C and mineralizable C were highest in NT, but the microbial C quotient, which averaged only 0.9%, was not affected by tillage or crop residue treatment. Microbial biomass C:N ratio was 11.3 in DT and 14.4 in the NT, indicating an increasing predominance of fungi with decreasing tillage intensity. Barley grain yield, which averaged 1980 kg ha −1 over the entire 17 years of the study, was highest in DO and not significantly different between NT and DT, but weeds were a serious problem in NT. Reduced tillage can improve important soil quality indicators and conserve organic matter, but long-term NT may not be feasible in the subarctic because of weed problems and build up of surface organic matter.

Growth and inhibition of single crystals of ethylene oxide clathrate hydrate provide experimental accessibility to similar phenomena in methane clathrate hydrates. Ethylene oxide hydrate single crystals were grown in a simple experimental setup. The crystals grew from the subcooled melt as rhombic dodecahedra, macroscopically exhibiting {110} as the slowest growing faces. The addition of minute amounts of poly(N-vinylcaprolactam) (PVCap) or a random terpolymer of PVCap, poly(N-vinylpyrrolidone), and dimethylaminoethylmethacrylate (VC-713) caused small-scale branching of crystals, but with a seemingly uniform crystal orientation. A few tenths of a weight percent of these additives caused complete crystal growth inhibition at several degrees of subcooling.

Thin plates, slender needle-like crystals, skeletal plates and skeletal linear forms can be produced in the free growth of cubic tetrahydrofuran hydrate from the melt, with growth rates differing by orders of magnitude on adjacent, crystallographically equivalent {111} faces. These anisotropic growth modes are distinctly different from each other and from the normal octahedral form. The growth of the solid plates and needles is unsteady, in that the fastest growth rates decrease with time, becoming nearly equal to those on the slower-growing faces. The skeletal plates and columns have steadier growth rates and are more common at higher values of supercooling. The most extreme solid needle and plate shapes occur at very low values of supercooling. While some or all growth forms that lack the cubic symmetry of the crystal structure may arise because of crystal imperfections that stimulate growth on some faces but not others, aspects of their growth are not straightforward to explain in this way. Po...

Different fish, insects, and plants have evolved a range of peptides and glycopeptides that adsorb to ice from water solution and dramatically influence ice growth in ways that benefit the organism...

Different fish, insects, and plants have evolved a range of peptides and glycopeptides that adsorb to ice from water solution and dramatically influence ice growth in ways that benefit the organisms. These “antifreeze” biomolecules are fairly large, the smallest so far discovered having a MW of 1600, and they prevent ice crystal growth from water at values of supercooling up to several degrees Celsius. Dealing with their interaction with the ice/water interface, one is faced with the choice of treating it as an adsorption-equilibrium phenomenon, in which the surface concentration adjusts easily to the solution concentration, or as irreversible adsorption, as if the molecules are very small particles that can achieve essentially permanent, equilibrium configurations at the ice/water interface. The two viewpoints each have areas of validity and usefulness, but the particle viewpoint is argued here to be the more insightful for the problem of understanding how the antifreezes produce their effects upon ice g...

Recently antifreeze proteins (AFP) have been the subject of many structure-function relationship studies regarding their antifreeze activity. Attempts have been made to elucidate the structure-function relationship by various amino acid substitutions, but to our knowledge there has been no successful from first principles design of a polypeptide that would bind to designated ice planes along a specific direction. In this paper we show the results of our first attempt on an entirely de novo design of an alanine-lysine-rich antifreeze polypeptide. This 43 residue alanine-lysine peptide exhibits characteristic nonequilibrium freezing point depression and binds to the designated (210) planes of ice along the [122] vector. The structural and thermodynamic properties of this polypeptide were determined using circular dichroism spectroscopy and its nonequilibrium antifreeze properties were investigated using an ice-etching method and nanoliter osmometry.

A recent report claims that the absence of prism facets on ice growing from slightly supercooled water at atmospheric pressure is due to the presence of air. We have reproduced the experiment and found the result to be incorrect: no prism facets are seen in an air-free environment.

Growth and inhibition of single crystals of ethylene oxide clathrate hydrate provide experimental accessibility to similar phenomena in methane clathrate hydrates. Ethylene oxide hydrate single crystals were grown from the supercooled melt as rhombic dodecahedra, exhibiting {1 1 0} as the slowest growing face. The addition of poly(N-vinylcaprolactam) (PVCap) or a random terpolymer of PVCap, poly(N-vinylpyrrolidone), and dimethylaminoethylmethacrylate causes small scale branching of crystals, but with a uniform crystal orientation. A few tenths of a weight percent of these additives cause complete crystal growth inhibition up to several degrees of supercooling.

Single crystals of structure II (sII) and structure I (sI) clathrate hydrates were grown in aqueous tetrahydrofuran (THF) and ethylene oxide (EO) solutions. Normal growth habits from the melt are predominantly {111} crystallographic planes for sII, and {110} for sI. Addition of polymeric so-called kinetic inhibitors in very small amounts changed the growth habit of sII to thin, 2-dimensional hexagonal {111} plates. Growing crystals in THF-rich or THF-poor solutions produced similar-looking flat plates. Adding the same inhibitors to the sI system caused rapid small-scale branching of the crystals. The highly branched sI specimens were found still to be single crystals. Higher concentrations of inhibitor were found to stop the growth of the crystals completely, for both sI and sII. These concentrations were as low as 0.1 wt.% at low supercooling. Experiments showed the polymers to be practically irreversibly adsorbed. A physical hypothesis was developed to explain the observed growth inhibition. This hypothesis appeals to a structural fit of the inhibitor polymers on the hydrate surface and strong bonding in specific configurations.

Three mutant polypeptides of the type I 37-residue winter flounder `antifreeze' protein have been synthesized. All four threonine residues in the native peptide were been mutated to serine, valine and glycine respectively and two additional salt bridges were incorporated into the sequences in order to improve aqueous solubility. The peptides were analyzed by nanoliter osmometry, the `ice hemisphere' test, the `crystal habit' test, measurement of ice growth hysteresis and CD spectroscopy. While the valine and serine mutants retain the α-helical structure, only the valine mutant retains `antifreeze' activity similar to that of the native protein. These data show that the threonine hydroxyl groups do not play a crucial role in the accumulation of the native `antifreeze' protein at the ice/water interface and the inhibition of ice growth below the equilibrium melting temperature.

Methane and nitrous oxide are important radiatively active gases that are influenced by agricultural practices. This study assesses long-term tillage, crop residue management, and N fertilization rates on the flux of these two gases at a high latitude site representing the northern fringe of large-scale agriculture. Cumulative methane uptake for the summer was higher from no-tillage plots than tilled plots. This was associated with lower soil water contents with tillage. Thus, the reduction in CH4 uptake was attributed to water stress on methane oxidizers. At planting, soil water contents were near field capacity, and the no-till plots had the lowest uptake which was attributed to restricted diffusion of methane to active sites. A similar pattern of methane uptake to soil water content was found with the residue management treatments. Removing the straw lowered the soil water content and for most of the season methane uptake was also lower than where the straw had been left on the plots. Nitrogen fertilizer rate had little effect on methane uptake over the summer, but high N rates lowered consumption during the time of active nitrification early in the season. This corresponded to the time of maximum efflux of nitrous oxide. Nitrous oxide efflux was greatest at the high N rate where straw was retained on the plots. Key words: Methane, nitrous oxide, nitrification, denitrification, barley

Tetrahydrofuran clathrate hydrate single crystals grow from the supercooled melt as octahedra, showing that {1 1 1} is the slowest-growing face. The addition of poly(vinylpyrrolidone), poly(vinylcaprolactam) or a random terpolymer of the previous two with dimethylaminoethylmethacrylate causes the crystals to grow as hexagonal plates also bounded by {1 1 1} faces. Plate thickness decreases with increasing concentration of the impurity, until growth is altogether inhibited at a concentration of polymer that depends on supercooling.

The root causes of atherosclerosis lie in cellular events that precede the clinical presentation of the disease by many years. The initiating events centre around the response of endothelial cells to chronic injury, such as that sustained in hypercholesterolemia. These responses involve the activation, attachment and migration of leucocytes and platelets.

DiDomenico and Eyrich question the definition of radiocontrast-induced nephropathy (RCIN) and whether contrast nephropathy occurred in the RAPPID study. The definition of RCIN employed (a rise in serum creatinine ≥25%) is a widely accepted one and has been used extensively [(1–4)][1].

Antifreeze glycopeptides (AFGPs) that adsorb to ice from liquid water solution and prevent ice crystal growth over a range of supercooling are found in the blood of some Antarctic fish. They are polymers with from four to about 52 monomer units. The shortest, with four and five of the repeating units, adsorb at prism-face orientations, (1010), aligned normal to the c-axis. The adsorption plane of the longer ones is (4150) when the concentration in solution is low. This may be the result of the 3% misfit with the ice structure, producing a bond strain that increases with increasing length of adsorbed AFGP. Jogs to an adjacent plane between every five adsorbed units can explain the new orientation. However, the adsorption plane reverts gradually back to (1010) with increasing concentration in solution. This and the effects upon ice growth habit are discussed in terms of the standard conceptual model of the adsorption of polymers at solid surfaces: adsorption of segments of the molecules, with loops and tails projecting into the solution from the interface. In contrast with the shorter AFGPs, the longer ones produce a novel interface instability caused by the adsorption-inhibition of growth, that produces a submicroscopically fibrous growth texture at higher solution concentrations.

Prudent use of agricultural fertilizers and herbicides is paramount for sustaining or improving surface and ground water quality in Subarctic regions, but little information is available that documents the loss of chemicals from agricultural lands in the Subarctic. This study aimed to ascertain more clearly how time of application and land management practices affect the loss of bromide and metribuzin in a Subarctic soil. Potassium bromide (KBr), a surrogate for nitrate, and metribuzin, commonly used to control broadleaf weeds, were applied in the autumn of 1996 and the spring of 1997 to a silt loam that had been subjected to conventional tillage (CT), minimum tillage (disk once [DO]), and no tillage (NT) since 1983. Superimposed on the tillage treatments were the removal or retention of barley ( Hordeum vulgare L.) stubble and loose straw. Loss of these chemicals was ascertained by sampling the soil profile at the time of heading of barley, before freeze-up of the soil in autumn, and after spring thaw until September 1998. Tillage and residue treatments did not influence the recovery of autumn-applied or spring-applied Br. However, recovery of Br diminished with time: about 30% of the Br applied in autumn and 45% of that applied in spring remained in the soil profile by September 1998. Tillage, but not residue, treatments influenced the recovery of metribuzin. Recovery of metribuzin at the termination of this study was 6% or more in NT soil and 2% or less in CT and DO soil; greater recovery in NT soil was presumably a result of slower degradation in NT than in CT and DO. This study suggests that bromide (and thus nitrate) and metribuzin are more prone to leaching when applied in autumn and that tillage practices affect retention of metribuzin, but not nitrate, in the soil of Subarctic Alaska.

It is widely accepted, and we agree, that the lowering of the temperature at which ice can grow in a water solution of one of the biological antifreezes is a result of adsorption of the antifreeze molecules at the ice surface. However, how this can produce a well-defined "freezing point" that varies with the solution concentration has remained problematical. The results of a series of measurements of ice growing in supercooled solutions of an effective antifreeze are reported and interpreted in terms of this fundamental problem. It seemed that the solution of the problem would have to rely upon adsorption rate, because that appeared to be the only way for the concentration in solution to be so important. The crystal growth results are most unusual, and appear to confirm this. The growth rates over a wide range of antifreeze concentration in solution (about 0.05 to 9 mg ml(-1)) are zero from the thermodynamic freezing point down to the "non-equilibrium" freezing point, where there is a very sudden increase to a plateau value that then remains about constant as the supercooling is increased by about 2 degrees C. The plateau values of growth rate are faster than those from pure water at the lower-supercooling ends of the plateaus, but slower at higher supercooling, until the growth rate starts rising toward that from pure water. These plateau values of growth rate increase markedly with increasing concentration of the antifreeze in solution. Along with these changes there are complex changes in the growth orientations, from c-axis spicules in the plateaus to those more characteristic of growth from pure water at greater supercooling. We conclude that the non-equilibrium freezing point is determined by the adsorption rate. It is the warmest temperature at which the ice growth rate on the basal plane (where the antifreeze does not adsorb) is fast enough to prevent the area of basal face on a growing ice crystal from becoming too small to grow, which is determined in turn by the adsorption rate on non-basal surfaces, which is proportional to the solution concentration. This mechanism answers the question of how the antifreeze stops growth rather than how it prevents growth, a subtle but important difference.

The noncolligative peptide and glycopeptide antifreezes found in some cold-water fish act by binding to the ice surface and preventing crystal growth, not by altering the equilibrium freezing point of the water. A simple crystal growth and etching technique allows determination of the crystallographic planes where the binding occurs. In the case of elongated molecules, such as the alpha-helical peptides in this report, it also allows a deduction of the molecular alignment on the ice surface. The structurally similar antifreeze peptides from winter flounder (Pseudopleuronectes americanus) and Alaskan plaice (Pleuronectes quadritaberulatus) adsorb onto the (2021) pyramidal planes of ice, whereas the sculpin (Myoxocephalus scorpius) peptide adsorbs on (2110), the secondary prism planes. All three are probably aligned along (0112). These antifreeze peptides have 11-amino acid sequence repeats ending with a polar residue, and each repeat constitutes a distance of 16.5 A along the helix, which nearly matches the 16.7 A repeat spacing along (0112) in ice. This structural match is undoubtedly important, but the mechanism of binding is not yet clear. The suggested mechanism of growth inhibition operates through the influence of local surface curvature upon melting point and results in complete inhibition of the crystal growth even though individual antifreeze molecules bind at only one interface orientation.

The use of pulsed ozone as a disinfecting agent in chilling water systems will be feasible only if components of the systems are not adversely affected. Pulsing ozone into water at room temperature for 20 minutes per day for 7 days caused greater weight loss of aluminium, carbon steel, copper, 304 stainless steel and 316 stainless steel samples than control samples; however, only weight loss for carbon steel was significantly greater (a = .05). Severe pitting was noted on ozone treated copper samples when observed by scanning electron microscopy. Black striations were observed on ozone treated carbon steel surfaces.

Special blood proteins present in fish that live in freezing sea water prevent ice growth in the blood to temperatures down to 1.5°C below its equilibrium freezing point (melting point) [1]. These compounds are peptides (AFPs) in some fishes, glycopeptides (AFGPs) in others, and range in MW from 3,300 to 33,000 daltons, and are collectively known as antifreezes (AFs). Similar proteins are found in the hemolymph of certain co]d-tolerant insects [2]. The antifreeze action appears to be the only reported case of crystal growth inhibition from the melt by a molecular solute as opposed to a gel-forming polymer. It is in effect an inhibition, not just a retardation of growth velocity. The temperature range over which an ice crystal neither melts nor grows is a sort of freezing hysteresis gap (Fig. 1). Beside the hysteresis, the AFs have a profound effect upon the habit of ice grown from water, reversing the anisotropy of growth rate from fastest along the a-axes to predominantly along the c__-axis.

This is a preliminary exploration of using hailstones as natural probes of cloud droplet chemistry Big hailstones grow primarily in the strongest updraft regions of the severest convective storms, so that if their chemical contents are representative of the cloud droplets from which they grow, they could be useful probes of chemical transport from the lower troposphere, where the anvils form and then evaporate. Results from chromatographic analyses of chloride, nitrate, nitrite, sulfate, and oxalate are presented from individual growth layers of hailstones collected from several different storms. In spite of considerable variability and possibilities of contamination from the ground, the results appear consistent enough to warrant further investigation of this possible source of data on cloud chemistry.

A new method for growing single crystals with sensitive control of supersaturation and minimal influence from foreign surfaces is described.

Evidence is presented that the nonequilibrium antifreeze peptide (AFP) from winter flounder has a special ability to inhibit recrystallization in ice only when an appreciable amount of liquid is present, as is the case when the system contains salts and the temperature is not too low. In this circumstance the AFP binds to the ice surface at the ice-solution interfaces in grain boundaries, preventing migration of the solution and effectively immobilizing the boundaries. In the absence of liquid, recrystallization inhibition appears to be a common property of many peptides. This is consistent with the view that the special effects of AFPs require a structural fit onto ice, and therefore require the AFP molecules to have the mobility to achieve that fit. Since the concentration of salt required to induce the special recrystallization inhibition effects of AFPs is lower (< 10 mM) than that found normally in physiological fluids, AFPs could play a role in the survival of organisms by preventing damage due to recrystallization. The proposition that mobility is needed for AFP molecules to produce their special influence upon ice growth argues against any special effects of AFPs in devitrification.

Reliable assessment of the effect of a solute upon ice recrystallization is accomplished with "splat cooling," the impaction of a small solution droplet onto a very cold metal plate. The ice disc has extremely small crystals, and recrystallization can be followed without confusing effects caused by grain nucleation. This method confirms the exceptionally strong recrystallization inhibition effect of antifreeze protein from Antarctic fish and shows that grain growth rate is a sensitive function of both grain size and solute concentration.

The results of a three-year randomized seeding experiment carried out as part of the National Hail Research Experiment are described in a nine-part series. In this first part the design of the statistical experiment is presented, including the physical hypothesis for hail suppression by seeding, the seeding procedures, the randomization scheme and the method of evaluation. The experiment was of the singlearea type and the randomization was by day. The criterion for selecting sample days involved the magnitude of radar returns from cumulonimbus clouds over and near the target area. Storms on approximately half the days were seeded according to a random selection procedure. The seeding method involved dispersing silver iodide in the storm updraft from aircraft maneuvering just below cloud base. An air-borne rocket system designed to deliver the nucleant at about the −5°C level in the storm was also employed in one season. The evaluation was based on the measurement of hailfall over a network of ins...

Three tillage practices were compared on a subarctic silt-loam soil to evaluate whether conservation tillage could be used effectively to reduce soil losses from wind erosion without delaying crop maturity or reducing yield. Urea and ammonium nitrate were also compared as sources of fertilizer nitrogen. Plots were cropped to rapeseed ( Brassica campestris L.) and barley ( Hordeum vulgare L.) in a rapeseed-barley-fallow rotation and in continuous barley. Zero-tillage did not delay maturity nor did it result in reduced yields except where there was excessive competition from perennial grassy weeds. Neither placement appeared to be less than optimum in zero-tilled plots. With proper fertilizer placement and grassy-weed control, conservation tillage appears to be a viable method of reducing the potential for wind erosion in the subarctic.

The process of the formation of new crystals at the interface between a crystal and its supercooled melt, by classical, heterogeneous nucleation, is examined theoretically and is suggested as a possible explanation for a number of crystal growth phenomena. Nucleation of new crystals at large angle lattice mismatches with the old, but at orientations such that the lattices “fit” across the interface is illustrated. Nucleation of new crystals appears to be responsible for the development of preferred orientations in deposits built up by the accretion of supercooled droplets, is advanced as an explanation for curved crystal growth, and is a possible explanation for some features of spherulites.

The major purpose of determining the water and ice nucleating effectiveness of atmospheric aerosols is to evaluate their effects upon cloud and precipitation formation. A review of classical heterogeneous nucleation theory shows the nucleating effectiveness to depend in an important way upon so many complex factors that the only possible approach is direct measurement. The same complexities affect both the measuring technique and the action of the aerosol within clouds. Consequently the techniques must be adapted to the kind of natural environment that the aerosol will encounter, in each specific case, before any important conclusions can be drawn from nucleus measurements.

When a rapidly freezing, water-ice interface approaches a water-air interface at a low angle, the water shirnks away from the advancing intersection line. This effect seems to indicate that γ IA γ IW + γ WA . The apparent intersection angle decreases with decreasing freezing rate, -a fact which is explained qualitatively by an increase of the slope of the water-ice interface adjacent to the contact line with decreasing freezing rate, caused by experimental conditions. A minimum value for the receding contact angle of water on ice is 12 ± 1° at slightly below 0°C., at a receding rate of about 1 cm./sec. on a somewhat rough surface. The possible error from the fact that the water-ice interface can not be observed directly is less than three degrees.

Nucleation rates on cylindrical nuclei are calculated using the classical theory. For very good but very small nuclei, the minimum cylinder radius that causes nucleation is about half that for spherical nuclei, other things being equal. The ice-supercooled water system is used for illustration.

The spectrum of a petroleum fluid inclusion, obtained from a producing oil well in the Gulf of Mexico, was compared with spectra obtained on three bulk oil samples produced from the same well. Comparison of the spectra of bulk and included petroleum samples shows several major differences. These differences are consistent with the loss of the more volatile components from the bulk oil samples.

The melting of pure ice single crystals can be inhibited by the presence of an antifreeze glycopeptide isolated from an Antarctic fish. This inhibition effect exhibits crystallographic dependence and can result in superheating of the crystal by heat conduction across the ice-solution interface. The antifreeze molecules inhibit melting in a manner more or less symmetrical to their well-known effect of inhibiting freezing. The melting effect is best expressed at concave ice interfaces, whereas the freezing effect is best expressed at convex ones. Both are restricted to orientations near (1010) with the particular antifreeze that was used.

Antifreeze glycopeptide and peptides from the blood of polar fishes prevent the growth of ice crystals in water at temperatures down to approximately 1 degree C below freezing point, but do not appreciably influence the equilibrium freezing point. This freezing point hysteresis must be a disequilibrium effect, or it would violate Gibbs' phase rule, but the separate freezing and melting points are experimentally very definite: ice neither melts nor freezes perceptibly within the 'hysteresis gap', for periods of hours or days. We report here unusual crystal faces on ice crystals grown from solutions of very low concentrations of the anti-freeze glycopeptides and peptides. This is a clue to the mechanism of freezing inhibition, and it may be the basis of a simple, very sensitive test for antifreeze material. Very low concentrations of the antifreeze protein are also remarkably effective in preventing the recrystallization of ice.

Holes bounded by crystal-lographic faces, or "negative" crystals, may be made in ice by inserting a hypodermic needle and connecting it to a vacuum. The evaporation habit changes as a function of temperature and growth rate. This procedure is a simple way of producing mirror-smooth, uncontaminated, crystallographic surfaces in compounds which have high vapor pressure.

But few diseases appeal more keenly to our sympathy than laryngeal phthisis. Extreme pain in swallowing, racking cough and stridulous breathing combine with other symptoms so well known to form a most distressing spectacle. A glance at the long list of medicines and measures which have been, at various times, advocated in its treatment proves the earnestness of the search for a remedy. Experiments with new drugs and new methods have been eagerly undertaken and hopelessly abandoned, until at last the majority of practitioners have settled down to the conclusion that palliative agents are the only resource. Of recent contributions lactic acid and menthol have, perhaps, attracted the most attention, in part because of the extraordinary claims made in their behalf. If the statements of Rosenberg, the most ardent champion of menthol, are to be accepted, we have in that drug almost a specific in laryngeal phthisis. His views have

Takahashi's calculation [J. Crystal Growth 59 (1982) 441] that hexagonal ice may nucleate as cubic ice applies for homogeneous nucleation. The special bicrystal orientations that he discusses have only been observed from heterogeneous nucleation, and may be explainable in another way.

Ice particles are collected from aircraft in sub-freezing silicone oil, with the aid of a simple decelerator, and brought back to the laboratory for study.

Internal melt figures can be nucleated in ice without the presence of a vapor bubble. Their form and growth are fracture-like, different from the normal Tyndall stars, which do contain vapor bubbles. Normal Tyndall figures that grow rapidly are not oriented in the basal plane, and very rapid internal melting gives a peculiar, systematic growth of clouds of Tyndall figures.

I REPORT here a method of studying the free growth from the melt of ice or any other material, at very small and very accurately controllable supercoolings. Helmholtz's experiment1 was brought to my attention by Dr E. LaChapelle, who discovered large, single ice crystals growing into water-filled cavities within a temperate glacier, and explained them by a natural variation of the present technique2.