bluuebunny/crossref_metadata_2025 huggingface dataset:
Macrophomina phaseolina in the Sonoran Desert
Authors: Mihail J. D. , Orum T. V. , Alcorn S. M. , Stroehlein J. L.
Published: September 2008

The relationship between microsclerotial populations of Macrophomina phaseolina (Tassi) Goid. and selected perennial species was investigated at five native Sonoran Desert sites. The population level of M. phaseolina was found to have an inverse relationship with the presence of several plant species, including Acacia constricta and Larrea tridentata, as measured by canopy cover, plant counts, and proximity of the soil sampling point to the nearest individual. Microsclerotia of M. phaseolina were detected in 45% of the 500 quadrats (3.3 m2) sampled, with a maximum observed population of 233 microsclerotia per 20 g soil. The microsclerotial populations of the five study sites showed significant aggregation as measured by Morisita's index of dispersion. No relationship was found between microsclerotial populations and soil pH, soil nitrate, or total soil nitrogen. The frequency of detection and population level of this agriculturally important pathogen raises questions concerning the role of the fungus in the Sonoran Desert ecosystem.
Influence of Penicillium frequentans and two of its antibiotics on production of stromata by Monilinia laxa in culture
Authors: Melgarejo P. , Cal A. De , M.-Sagasta E.
Published: September 2008

The influence of an isolate of Penicillium frequentans and two of its antibiotics on the mycelium of Monilinia laxa in culture has been studied using light and electron microscopy. Penicillium frequentans and antibiotic B induced the development of continuous stromata in cultures. Stroma production in colonies exposed to antibiotic A is rhythmic, with alternating zones of normal development of the mycelium. Abundant pycnidium-like structures, within which microconidia of M. laxa were formed, were produced on the induced stromata of cultures exposed to Penicillium and antibiotic A. The presence of melanin-like pigments in normal and induced stromata of M. laxa was also demonstrated and quantified.
The concept of soil infectivity and a method for its determination as applied to Endomycorrhizas
Authors: Plenchette C. , Perrin R. , Duvert P.
Published: September 2008

The concept of soil infectivity, widely used for soil-borne plant pathogens, is applied to the fungi forming vesicular–arbuscular endomycorrhizae. The authors propose a method for the determination of the mycorrhizal soil infectivity (MSI) using leek, a highly mycotrophic plant, for the bioassays. Under controlled conditions, populations of leek plants are grown in a range of concentrations of a natural soil mixed with autoclaved volumes of the same soil. The relationship between the percentage of plants forming mycorrhizae and the soil concentration is used as the basis for the determination of the quantity of soil required to obtain mycorrhiza formation on 50% of the host plant population; the results are defined in terms of MSI units and are expressed as MSI50 for 100 g of soil. The features of the method are illustrated in a comparative study of four agricultural soils from France.
Fine structure of the microsymbiont of the actinorhizal root nodules of mountain mahogany (Cercocarpus ledifolius, family Rosaceae)
Authors: Wood Susan M. , Newcomb William , Nelson David
Published: September 2008

Root nodules of Cercocarpus ledifolius Nutt. (mountain mahogany) were studied by light microscopy, scanning electron microscopy, and transmission electron microscopy to confirm the bacterial nature of the microsymbiont and to determine the morphology of the symbiotic vesicles. The microsymbiont is an actinomycete having two morphologies: septate hyphae (ca. 0.5 μm diam.) and ovoid- or elliptical-shaped nonseptate symbiotic vesicles (2.8 × 3.9 μm). Many of the symbiotic vesicles contain a single, electron-dense ovoid- or spherical-shaped structure, measuring 0.26 μm, whose function is unknown. The actinomycete is surrounded by a capsule that has electron-dense droplets in regions near hyphae. No spores or sporangia were observed in these nodules.
Biosystematic studies on the Stellaria calycantha (Caryophyllaceae) complex. I. Cytology and cytogeography
Authors: Morton J. K. , Rabeler R. K.
Published: September 2008

Stellaria calycantha consists of two species, a diploid (2n = 26) S. calycantha (Ledeb.) Bong. and a tetraploid (2n = 52) S. borealis Bigelow. Two subspecies are recognized in S. borealis: the widespread ssp. borealis and the western North American ssp. sitchana (Steudel) Piper. Part of the range of variation in the complex is due to hybridization between S. borealis and S. longifolia (2n = 26). These hybrids are all sterile triploids. Chromosome numbers are also reported for S. longifolia Muhl., which is consistently diploid (2n = 26), S. crispa Cham. & Schldl., which has diploid and tetraploid races (2n = 26 and 52), and S. obtusa Engelm., which is diploid and polyploid with 2n = 26, 52, c65, and c78. A key is provided to distinguish the taxa, together with maps showing the distribution of several of the taxa.
Biosynthèse des pectines et différenciation des fibres cellulosiques au cours de la croissance du lin
Authors: Morvan O. , Jauneau A. , Morvan C. , Voreux H. , Demarty M.
Published: September 2008

During the first stage of flax growth, stem elongation reaches 2.4 cm per day and the percentage of cell wall remains quite constant (4–15%). Cellulosic fibres develop principally during capsule formation and seed maturation. During the latter stage, the proportion of walls increases from 15 to 60% and the elongation is diminished to 0.5 cm per day. The lowering of the cation exchange capacity and of the pectin content of the cell walls during growth results principally from increased cellulose deposition in the fibre cells. The changes in the cation exchange capacity and in the percentage of cell wall show that when cellulose biosynthesis predominates, there is a continuous synthesis of pectins (10–15%) during the development of the plant. Methylated pectins are synthesized during the elongation phase. During maturation, the relative amounts of highly and less methylated pectins remain the same and thus it is not possible to determine what type of pectin is preferentially synthesized.
The morphological basis of variation in net photosynthetic and respiratory responses of the mat-forming lichen species Stereocaulon virgatum and S. tomentosum
Authors: Coxson D. S. , Lancaster J.
Published: September 2008

Response patterns of net photosynthesis and dark respiration are examined in two species of Stereocaulon: S. tomentosum Fr., from early successional pine forest communities of the southern Canadian Rockies, and S. virgatum Ach., an early colonizer in tropical cloud-forest environments. These responses, measured in both intact and dissected mat segments, are described in the context of the influence of morphological variations on patterns of water vapor transport. Saturation response curves are fitted to data, allowing description of maximal rates of both net photosynthesis and dark respiration, water contents at which rates are half maximal, maximal water efficiency, and moisture compensation points. In S. tomentosum the closed-canopy nature of the lichen mat profile results in the development of a distinct shade ecotype in lower thallus segments. This canopy profile also impedes water vapor transport from within the mat profile, creating a more mesic microclimate for photobionts located at depth within the lichen mat. This stands in contrast to the open upper canopy profile of S. virgatum, which allows greater convective exchange at depth and appears to preclude the development of distinct sun–shade photobiont ecotypes. Net photosynthetic activity remains high in fully saturated thalli of S. tomentosum, yet in S. virgatum it is depressed by over 50% at full thallus saturation. This greater depression of photosynthetic uptake at full thallus saturation in the species of the more mesic environment contradicts a priori assumptions based on previous concepts of xeric–mesic response gradients in lichens. These responses are discussed in context of other selective pressures influencing lichen mat morphology.
Studies on sucrose requirements of cultured maize tassels
Authors: Pareddy D. R. , Greyson R. I.
Published: September 2008

The role and metabolism of sucrose in cultured tassels of Zea mays cv. Oh43 were investigated. Although cultured tassels required 0.3 M (10% w/v) sucrose for "normal" development, they consumed less than 50% of it by day 21 of culture. The substitution of sucrose with mannitol inhibited both tassel growth and spikelet development. Sucrose served, therefore, mainly as an energy source and not as an osmoticum for cultured tassels during the first 15 days. However, from 15 days of culture onwards, tassels were shown to be capable of CO2 fixation and consumed negligible amounts of sucrose until day 21 of culture. Nevertheless, the presence of sucrose was shown to be essential for differentiation of "normal" spikelets.
Cytokinin effects on pollen embryogenesis in cultured anthers of Hyoscyamus niger
Authors: Raghavan V. , Nagmani R.
Published: September 2008

Addition of the cytokinins, benzylaminopurine, N6-Δ-(2-isopentenyl)-adenine, kinetin, zeatin, and zeatin riboside to a basal medium containing mineral salts and sucrose induced characteristic changes in pollen embryogenesis in cultured anthers and anther segments of Hyoscyamus niger. In anthers cultured in media containing 0.01–10.0 mg/L of each cytokinin, there was a progressive delay in the appearance of plantlets outside the anther locule and in the morphology of plantlets formed. Among the cytokinins tested, only zeatin riboside promoted anther efficiency; however, all compounds reduced pollen efficiency by as much as 40–60% of the control even in the lowest concentration tested. The effects of cytokinins were particularly noticeable in the failure of pollen grains to form embryoids by the division of the generative cell and in the decrease in the number of embryoids formed by the division of both generative and vegetative cells. At the morphogenetic level, embryoids formed in media containing cytokinins displayed various abnormalities such as precocious elongation of the root apex, cotyledon expansion, and callus formation on the cotyledons, hypocotyl, and root. During their subsequent growth, calluses induced on embryoids by benzylaminopurine, N6-Δ-(2-isopentenyl)-adenine, zeatin, and zeatin riboside formed somatic embryos that recapitulated stages of zygotic embryogenesis. Globular and heart-shaped embryoids, which did not develop further, were frequently observed on kinetin-induced pollen callus; the callus also regenerated leafy shoots by organogenesis. Addition of adenine to the medium did not have any effect on pollen embryogenesis in cultured anthers of H. niger.
Species richness – standing crop relationships along four lakeshore gradients: constraints on the general model
Authors: Wisheu Irene C. , Keddy Paul A.
Published: September 2008

The applicability of a model describing the relationship between species richness and standing crop and litter was tested in each of four lakeshore habitats within Wilsons Lake, Nova Scotia. The shapes of the curves describing the species richness – standing crop relationships in the four habitats were significantly different. Standing crop and litter values were positively correlated with measured indices of soil fertility (loss on ignition and silt and clay content) and negatively correlated with disturbance as determined by the location of the shrub zone and overwinter damage to wooden pegs. Sites with high standing crop had a lower proportion of biomass composed of evergreen and isoetid species than the proportion in sites where standing crop was low. The among habitat variation observed in this study, and the variation in published values of standing crop values yielding maximum species richness, limit the accuracy of predictions from this model. Steps for refinement are suggested.
Water relations, gas exchange, and early growth rates of outcrossed and selfed Pinus banksiana families
Authors: Blake T. J. , Yeatman C. W.
Published: September 2008

Seedlings of six outcrossed jack pine (Pinus banksiana Lamb.) families from a diallel cross of jack pine were mainly larger than those of three selfed families at the time they were transplanted to the field in Ontario. Outcrossed families also exhibited a greater absolute and relative (percent) growth in total dry matter at the end of the first growing season. Outcrossed families exhibited a higher net photosynthesis, a lower transpiration rate, and a higher water use efficiency on hot, but not mild, days in mid-August. Stomatal conductance, transpiration rate, and net photosynthesis were greater in outcrossed families in September. There were significant, positive correlations between stomatal conductance, transpiration rate, and shoot and root growth in August and September. The results suggest that maintenance of a higher stomatal conductance and net photosynthesis until late in the growing season may contribute to the faster growth rates observed in outcrossed families.
Chrysophycean stomatocysts from the postglacial sediments of Tasikutaaq Lake, Baffin Island, N.W.T.
Authors: Duff Katharine E. , Smol John P.
Published: September 2008

Twenty chrysophycean stomatocysts were described from the postglacial sediments of a Mid Arctic lake (Tasikutaaq Lake, Baffin Island, N.W.T.). The description guidelines of the International Statospore Working Group were followed. Elements of both High Arctic and temperate cyst floras were present, and approximately one-third of the cysts were described as new. Stomatocyst degradation was common and may be related to the degree of ice cover on the lake.
Effects of soil temperature and depth on colonization and root and shoot growth of barley inoculated with vesicular–arbuscular mycorrhizae indigenous to Canadian prairie soil
Authors: Volkmar K. M. , Woodbury W.
Published: September 2008

The ability of vesicular–arbuscular mycorrhizae indigenous to the Canadian prairie to colonize roots and promote growth of barley in 38 × 11 cm plastic tubes at soil temperatures of 12, 16, or 20 °C was examined. Mycorrhizal inoculum was placed 5 cm below the soil surface (PI) or dispersed throughout the soil (DI) prior to planting. Plants were harvested at stage 10.1 (Feeke's scale). Infection levels on PI and DI treatments were about 2 and 7%, respectively, with more infection occurring on DI roots. Soil temperature did not influence infection of DI plants but infection development beyond the inoculum source was greatest at 12 °C in PI plants. The dry shoot mass of DI plants was larger, but root mass was smaller than the PI and control plants irrespective of soil temperature. Root lengths of PI and DI plants were about 80 and 40% of control plants, irrespective of soil temperature with root length declining with soil depth on PI and control plants but not on DI treatments. Low infection level despite high inoculum potential indicated either a low rate of overwinter inoculum survival or an incompatibility between the host and endophyte. Significant growth promotion in spite of low levels of infection suggests that the mycorrhizal species that do colonize the root could be of economic value.
A Petri dish technique for the aseptic synthesis of ectomycorrhizae
Authors: Wong Ken K. Y. , Fortin J. André
Published: September 2008

An improved technique was developed for the aseptic synthesis of ectomycorrhizae in Petri dishes. Within 2 weeks after inoculation of a first-order lateral, ectomycorrhizae were formed on Larix laricina and Pinus banksiana with Hebeloma cylindrosporum, Laccaria bicolor, and Pisolithus tinctorius. The technique should be useful for addressing physiological and biochemical questions concerning microbial interactions with roots of whole plants.
Abrupt downstream forest decline following river damming in southern Alberta
Authors: Rood Stewart B. , Heinze-Milne Sig
Published: September 2008

The influence of river damming on the abundance of riparian poplar forests was investigated by comparing forest abundances on the dammed St. Mary and Waterton rivers of southern Alberta with the neighbouring undammed Belly River. Forest distributions were determined by estimating the linear river distance of forests from airphotos taken in 1961 and 1981, both upstream and downstream from the dams. During the 20-year interval, a 48% reduction occurred downstream from the St. Mary Dam, which was completed in 1951. Downstream from the Waterton Dam, completed in 1964, riparian forests declined 23 %. Poplar abundance along the downstream region of the undammed Belly River was relatively unchanged over the study period, showing less than a 1 % reduction. The upstream (undammed) portions of all three rivers underwent a slight forest decline during the 20-year interval; declines of 4.7, 4.6, and 6.1 % occurred along the St. Mary, Belly, and Waterton rivers, respectively. Thus, the damming of two rivers in southern Alberta has been followed by a rapid and dramatic downstream decline in riparian forests. Further, the close association between the location and extent of the forest decline supports a causal relationship between the river damming and the forest decline. Possible causes of the decline are discussed, including drought-induced mortality, particularly of seedlings.
Growth characteristics of Laccaria laccata and Paxillus involutus in liquid culture media with inorganic and organic phosphorus sources
Authors: Hilger Arlene B. , Krause Helmut H.
Published: September 2008

Two ectomycorrhizal species, Laccaria laccata (Scop, ex Fr.) Berk & Br. and Paxillus involutus (Batch, ex Fr.) Fr., were grown aseptically in liquid media to determine their ability to use soluble phytate as a sole source of phosphorus. Efficiency of glucose utilization and rates of acid production were also determined. Both species grew well with phytate as the sole source of phosphorus and released large amounts of inorganic phosphorus to the medium. However, L. laccata hydrolysed the phytate during exponential growth, whereas P. involutus cultures showed accumulation of inorganic phosphate during the senescence stage, suggesting that hydrolysis was occurring after release of intracellular phosphatases from lysing cells in the latter case and by surface-active enzymes in the former. Paxillus involutus had a lower glucose utilization efficiency per unit biomass than L. laccata. Paxillus involutus also acidified the growing medium more strongly than L. laccata and it released large amounts of pigmented substances into the medium.
Initiation of embryogenic callus and suspension cultures, and improved embryo regeneration from protoplasts, of white spruce (Picea glauca)
Authors: Attree S. M. , Dunstan D. I. , Fowke L. C.
Published: September 2008

Rapid and high frequency somatic embryo regeneration from protoplasts isolated from 10 embryogenic cell lines of white spruce (Picea glauca) is reported. Embryogenic callus was initiated from immature zygotic embryos as source material for protoplast isolation. Individual cell lines exhibited different capabilities for sustained growth. Protoplast plating efficiencies depended on the concentrations of macroelements included in the medium. Using a medium with reduced salts, individual protoplasts developed directly into embryos with no disorganized growth period. Protoplasts from newly established suspension cultures regenerated to recognizable somatic embryos within 8 days of culture. This embryo development was faster than that from protoplasts isolated from longer term suspension cultures. However, the latter suspensions yielded more protoplasts, displayed higher plating efficiencies, and differed in their response to media.
Effects of simulated acid precipitation on the metabolic activity of Cladina stellaris
Authors: Roy-Arcand Line , Delisle Claude E. , Brière François G.
Published: September 2008

Cladina stellaris (Opiz) Brodo specimens, collected from Kuujjuarapik, Quebec (55°29′N, 77°07′W), were kept for 8 weeks in growth chambers and sprayed every day with simulated acid-rain solutions to study the effects of rain pH and sulfate to nitrate ratios on the lichen. The acidity of the solution was adjusted to obtain pHs of 2.0, 3.0, 4.0, and 5.0, and the sulfate to nitrate ratios studied were 2:1 and 6:1 μequiv.∙L−1. Metabolic responses of the lichens to the acidification treatments were assessed by measurements of the number of algal cells, the amount of chlorophyll a, and the basal and resaturation respiration rates. At pHs of 2 and 3, the metabolic activity of young podetial tips of C. stellaris was significantly reduced, whereas the treatments at pH 4 and 5 enhanced growth. Alteration of the sulfate to nitrate ratios in the precipitation did not produce any significant differences in the measured metabolic activity. Cladina stellaris responses to the quantity and quality of acidification are summarized in a set of regression models that emphasize a threshold response to acid precipitation near 3.5; below pH 3.5, metabolism is impaired, whereas above pH 3.5; some metabolic responses are enhanced.
Biogeography of island floras in the Great Lakes. II. Plant dispersal
Authors: Morton J. K. , Hogg E. H.
Published: September 2008

Experimental and observational data were used to determine the adaptations for dispersal in each of the 335 vascular plant species in the flora of Barrier Island, a typical limestone island in the Great Lakes. Most have adaptations for more than one mode of dispersal. Adaptations for dispersal by water were found in 211 species (63% of the flora), and by birds in 205 species (61% of the flora); only 22 species (6.5% of the flora) do not appear to have effective adaptations for dispersal by either of these means. The other three modes of dispersal to these islands are by wind (14% of plant species), dispersal across snow and ice (10%), and by man (6%). Alien species (23% of the flora) show greater dependence on birds (85% of the alien species) and man (12% of the alien species) for dispersal than do native species (54 and 5%, respectively). Sea gulls, particularly the Herring Gull (Larus delawarensis Ord.), are the major factor in the introduction of the alien flora. The heavily disturbed habitats created in the nesting sites of both Herring and Ring-billed (Larus argentatus Pontoppidan) gulls favour the persistence of many alien plant species on these islands.
Comparison of achene characteristics within and among diploid and tetraploid clones of Solidago flexicaulis and their significance in germination and resource allocation studies
Authors: Chmielewski J. G. , Semple J. C. , Burr L. M. , Hawthorn W. R.
Published: September 2008

Achene characteristics were examined within clones, among clones of a cytotype, and between the diploid and tetraploid cytotypes of Solidago flexicaulis. The pattern of intraclonal variation was similar in each of the three diploid and five tetraploid clones. In each of the clones, embryo weight increased with increasing achene weight and the number of days taken to germinate increased with increasing pericarp weight. Other significant correlations were not consistent among all clones. Generally, clones of the same cytotype were more similar to each other than to clones of the other cytotype. Additionally, the characteristics were generally larger among the tetraploid than diploid clones. However, a trend in decreasing size from southwestern to southeastern Ontario was observed. With respect to most measured characteristics, tetraploid clones occurring just west of the Frontenac Axis were intermediate between tetraploid clones occurring farther southwest in Ontario and diploid clones occurring just east of the Frontenac Axis. In this study, knowledge of ploidy level was important not only with respect to the analyses performed but also with respect to the interpretation of results and the correct assessment of causal factors of observed patterns of variation. Thus, knowledge of ploidy level is especially important in comparative ecological studies involving patterns of resource allocation and germination rates.
Isozyme evidence of pycnial fertilization by urediniospores of the bean rust fungus
Authors: McCain John W. , Groth J. V.
Published: September 2008

Some asexual isolates of the bean rust fungus, Uromyces appendiculatus, exhibit unusual isozyme and host-specific virulence traits. As a hybridization method not involving donor spermatia, urediniospores were applied to receptor pycnia. Aecia developed in a minority (< 10%) of the trials. Inoculations with first sibling generation urediniospores of the putative hybrid progeny on five differential bean lines often produced infection types that matched those of the maternal parent; therefore virulence did not clearly indicate successful crossing. However, urediniospore isozyme patterns containing bands from both parents for six enzymes confirmed hybridization in 7 of 14 progeny. Bands for the remaining progeny matched the maternal parent, indicating origin by selling. Thus, the electrophoretic results indicate that, in the bean rust fungus, urediniospores sometimes can act as spermatia (nuclear donors) for fertilization of pycnia. Pycnium × uredinium crossing should prove to be a useful technique for genetic studies of asexual rust populations.
Morphology of Sclerotium coffeicola, a tropical foliar pathogen
Authors: Hanlin Richard T. , Tortolero Omar
Published: September 2008

Sclerotium coffeicola, the cause of target-spot disease of coffee, is reported from Venezuela for the first time. Target spot is a foliar disease characterized by large brown lesions composed of a series of concentric rings. Columnar bundles of hyphae (propagules) form on the undersides of the leaves. Orange sclerotia are produced on infected host tissues and in culture. Hyphal septa are sparse and are of the dolipore type. The sclerotia develop from loose aggregations of interwoven hyphae that become more compact as the sclerotia mature. As the sclerotia develop, most interior hyphae enlarge into inflated, thin-walled cells that are interspersed with scattered, broad, thin-walled hyphae. Circular areas of pseudoparenchymatous cells form in the periphery of the sclerotia where they secrete liquid droplets. The outermost layer or two of cells have slightly thickened walls and are pigmented, but the interior of the sclerotium remains white. The entire sclerotium is covered by two thin layers of an amorphous material.
Climate and annual ring growth of black spruce in some Alberta peatlands
Authors: Dang Q. L. , Lieffers V. J.
Published: September 2008

The long-term relationship between climate and tree-ring growth in black spruce (Picea mariana (Mill.) B.S.P.) was determined in two peatland sites near Slave Lake, Alberta. At each site, 15 dominant – codominant black spruce were sampled for tree-ring growth at 30 cm height. The tree-ring indices for each site were related to precipitation and temperature data from Slave Lake. It was found that (i) tree-ring indices were positively correlated with June – August precipitation of the current year and of the 1st and 2nd years prior to the current year; (ii) June – August maximum temperatures of the current year and of the 1st and 2nd years prior to the current year were negatively correlated with tree-ring indices; (iii) tree-ring indices had a positive linear correlation with the June – August minimum temperature of the current year and polynomial correlations with June – August minimum temperatures of the 1st and 2nd years prior to the current year; and (iv) summer precipitation values greater than 325 mm probably had a negative impact upon the tree-ring growth. Maximum and minimum temperatures, however, were intercorrelated with precipitation. Key words: dendrochronology, climate, tree rings, peatlands, mire.
Vasculature of the abscission zone of tomato fruit: implications for transport
Authors: Lee D. R.
Published: September 2008

The structural anatomy of the abscission zone in the "knuckle" of the pedicel supporting the tomato fruit may provide an explanation as to how and why a fruit such as a tomato (Lycopersicon esculentum) can accumulate both water and dry matter. There is a significant reduction in xylem and a major increase in phloem cross-sectional area through the knuckle relative to the rest of the pedicel that persists from flowering through to fruit maturity. This will produce a site of high resistance to water flow in the xylem and transfer the demand for water by the fruit to the phloem, thus linking water and dry matter influx into the fruit. Transpiration from the fruit will play a role in initiating or maintaining the flow of phloem sap to the fruit.
The morphology and relationships of Thuja polaris sp.nov. (Cupressaceae) from the early Tertiary, Ellesmere Island, Arctic Canada
Authors: McIver E. E. , Basinger J. F.
Published: September 2008

Fossil foliage and seed cones of Thuja (Cupressaceae) have been discovered in early Tertiary (Paleocene) sediments of the Eureka Sound Group on Ellesmere Island, Canadian Arctic Archipelago. Vegetative remains of the fossil species, Thuja polaris sp.nov., bear alternately branched, moderately divided, flattened, and pinnatelike sprays with scale-like, decussate leaves. Seed cones are oblong, bearing 8 – 9 pairs of thin, probably leathery cone scales with distinct, reflexed umbos. Fossil cones and foliage resemble closely those of extant Thuja plicata. However, fossil seed cones have twice as many pairs of scales as do extant species of Thuja. A review of the fossil record indicates that most Thuja-like vegetative remains which have been reported from Cretaceous and Tertiary deposits in the Northern Hemisphere are best assigned to form taxa and not to extant genera. Reproductive material from four Tertiary localities can be assigned to Thuja on the basis of seed cone structure. The evolutionary history of the genus, based on fossil and extant seed cone morphology, appears to include a reduction in the number of cone scales. Extant species form a closely related, natural group and, with the exception of T. sutchuenensis, may have arisen from an ancestor similar to T. polaris. Although Thuja was widespread in the Northern Hemisphere during much of the Tertiary, the genus is now confined to northeastern and northwestern North America, and to Japan, Korea, and central China.
Ethylene production, georesponse, and extension growth in dandelion peduncles
Authors: Clifford P. E. , Oxlade E. L.
Published: September 2008

Using gas chromatography, it was demonstrated that elevated levels of endogenous ethylene were associated with the diageotropic behaviour and reduced extension growth exhibited by Taraxacum peduncles after flowering. The Taraxacum peduncle appears to be an excellent experimental model to elucidate the role of ethylene in regulating both geotropism and cell elongation.
Gene expression during the infection process in nodulating and nonnodulating pea genotypes
Authors: Gal M. F. Le , Hobbs S. L. A. , Delong C. M. O.
Published: September 2008

Pea (Pisum sativum L.) cv. Afghanistan inoculated with Rhizobium leguminosarum biovar. viciae aborts the nodulation process if North American strains are used but will form effective nodules with strain TOM. Early nodulins (nodule specific root proteins) were examined by in vitro translation of total root or root + nodule RNA and two-dimensional gel analysis. Qualitatively different protein patterns were found between effective nodulation in Trapper (a North American variety) and 'Afghanistan' and between effective and abortive nodulation in 'Afghanistan'. Six days after inoculation a 26-kDa protein was evident that was only produced in Trapper roots and several nodulins were visible. Nodulin N-37 was present in effective and abortive combinations. Nodulin N-52 was present in inoculated Trapper but not in inoculated 'Afghanistan', whereas N-23 was present in inoculated 'Afghanistan' but not in inoculated Trapper. Nodulin N-58 occurred only in abortive combinations with 'Afghanistan'. Nonnodulating Trapper (Trapper into which the nonnodulation genes of 'Afghanistan' had been back-crossed) showed the same patterns of gene expression as 'Afghanistan'. The expression of several genes apparently differs between 'Afghanistan' and Trapper for the nodulation process.
Seasonal isolation as a reproductive barrier among sympatric Salix species
Authors: Mosseler A. , Papadopol C. S.
Published: September 2008

Differences in flowering phenology may be an important premating reproductive barrier between willow species. The seven sympatric species studied fall into two flowering groups within which there is substantial seasonal overlap: an early flowering group that includes Salix bebbiana Sarg., Salix discolor Muhl., Salix eriocephala Michx., and Salix petiolaris Smith, and a later flowering group that includes Salix amygdaloides Anderss., Salix exigua Nutt., and Salix lucida Muhl. The species flowering sequence was reasonably consistent over the 3-year period from 1984 to 1986. Thermal control over flowering phenology was related to cumulative growing degree-days. The inheritance of phenological responses in artificially produced F1 interspecific hybrids was intermediate between that of the parental species.
Influences of the new auxins 4-carbomethoxyvinylenephenyl indole-3-butyrate and 2, 4-dichlorophenyl indole-3-butyrate on adventitious root formation
Authors: Haissig Bruce E.
Published: September 2008

Tests were conducted with cuttings of bean (Phaseolus vulgaris L. cv. Top Crop) and jack pine (Pinus banksiana Lamb.) seedlings to determine the influences of the new auxins 4-carbomethoxyvinylenephenyl indole-3-butyrate (CMVP-IBA) and 2,4-dichlorophenyl indole-3-butyrate (DCP-IBA) on adventitious rooting. For comparison, bean cuttings were used to determine the effects on adventitious rooting of the unsubstituted phenyl ester of IBA, phenyl indole-3-butyrate (P-IBA). Results indicated that, compared with IBA, treatment with CMVP-IBA resulted in less adventitious rooting of jack pine and bean cuttings, treatment with DCP-IBA resulted in equal adventitious rooting of jack pine and bean cuttings, and treatment with P-IBA resulted in greater rooting of bean cuttings (jack pine was not tested). Based on results of the present and previous research, the phenyl esters of indole auxins have equal or greater root-inducing activity, compared with the parent auxin, only if their phenolic moieties do not contain a substituent (e.g., P-IBA) or contain only a simple substituent such as -OH (e.g., 3-hydroxyphenyl indole-3-acetate) or -Cl (e.g., DCP-IBA), rather than a more complex substituent like -CH=CH—COOCH3 (e.g., CMVP-IBA). However, further research is needed to test the accuracy of these generalizations.
Ultrastructural studies of primary spores of Conidiobolus, Erynia, and related Entomophthorales
Authors: Latgé J. P. , Perry D. F. , Prévost M. C. , Samson R. A.
Published: September 2008

Wall development during primary spore formation, discharge, and germination of Entomophthorales is emphasized in ultrastructural studies of Conidiobolus, Entomophaga, Neozygites, and Erynia. In the fungi examined, spore and sporophore walls consist of a thick, electron-translucent inner layer and a thin, electron-dense outer layer. During spore formation, cytoplasm of the supporting sporophore cell migrates into the spore initial. As the former cell empties, a septum develops. Discharge is caused by inversion of the papillum, which lacks the electron-dense layer. Only in Erynia did the two spore wall layers separate upon impact. Intracytoplasmic organization of the primary spore is typical of the Zygomycotina; the morphology of organelles was characteristic of species, whereas nuclear ultrastructure was consistent within genera. Conidiobolus nuclei have a prominent nucleolus that lacks heterochromatin, in contrast with the other genera where large patches of heterochromatin were observed. Upon germination, no rupture of the spore outer layer was observed other than at points of germ tube emergence. The germ tube wall was continuous with the inner spore wall layer. The results are discussed in reference to Entomophthorales taxonomy and definition of the terms conidium and monosporous sporangiolum.
Does growth rate determine leaf form in Pisum sativum?
Authors: Gould Kevin S. , Cutter Elizabeth G. , Young J. Peter W.
Published: September 2008

We have examined the long-standing hypothesis that leaves are morphologically more complex following prolonged proximity to the shoot apical meristem. Growth rates of the petiole and rachis of conventional and mutant pea leaves were compared for successive nodes of insertion in seedling plants. Leaves were longer at higher nodes, though the relative growth rate did not vary. Mature afila leaves were longer than those of conventional and tendril-less genotypes. The afila leaf alone exhibited a transient, highly significant rise in relative growth rate during the plastochron interval P4.5–P5.5. This rise occurred after the stage at which leaves of the different genotypes were anatomically distinguishable (stage P2–P3). Rates of vertical displacement of the leaf primordium from the shoot apical meristem did not differ significantly among genotypes. Our data suggest that the rate of leaf extension is one of the consequences, rather than a cause, of leaf morphology.
Relationship between mycorrhizal dependence and competitive ability of two tallgrass prairie grasses
Authors: Hetrick B. A. D. , Wilson G. W. T. , Hartnett D. C.
Published: September 2008

The impact of mycorrhizal symbiosis on growth of Andropogon gerardii (big bluestem) and Koeleria pyranidata (junegrass) was compared. Andropogon gerardii was 98% dependent on the symbiosis, whereas K. pyranidata displayed less than 0.02% dependence. Mycorrhizal fungus inoculation resulted in 50 times larger A. gerardii plants but did not alter growth of K. pyranidata. When competing in pairs, A. gerardii dominated when the mycorrhizal symbiosis was present and K. pyranidata dominated when it was not present. Dry weight of mycorrhizal A. gerardii was altered, whether grown alone or with K. pyranidata, but mycorrhizal K. pyranidata grew well only in the absence of competition and failed to grow appreciably if A. gerardii was present. Without mycorrhizal fungus inoculation, A. gerardii did not grow and had no deleterious effects on K. pyranidata. When P fertilization was substituted for mycorrhizal fungus inoculation, A. gerardii grew better alone than in competition with K. pyranidata at low P levels but was not affected by competition at high P levels. Koeleria pyranidata was not affected by competition at low P levels, but high P fertilization resulted in reduced dry weight of K. pyranidata plants when in competition with A. gerardii. Phenologic separation of growing seasons avoids interspecific competition between these two grasses and may be one mechanism contributing toward their coexistence. Since low temperatures limit mycorrhizal nutrient uptake, phenologic separation of growing seasons could also avoid the competitive advantage of warm-season grasses conferred by their mycorrhizal dependence.
Local competition in a naturally established jack pine stand
Authors: Kenkel N. C. , Hoskins J. A. , Hoskins W. D.
Published: September 2008

The spatial pattern of 1375 jack pine individuals (459 live, 257 standing dead, and 659 stumps) in a pure, even-aged, naturally established stand was mapped. Three maps corresponding to different stages of stand development were recognized: live + dead (initial pattern, n = 1375), live (following self-thinning, n = 459), and live + standing dead (survivors plus most recent mortality, n = 716). The Dirichlet-Thiessen tessellations of these maps indicated that the distribution of tile areas (area potentially available) becomes increasingly equitable over time. A significant positive correlation between diameter at breast height of surviving trees and their area potentially available was found for each map; this correlation was highest for the live tessellation. In the live + dead and live + standing dead tessellations, the mean tile area of dead trees was significandy smaller than that of survivors. The spatial pattern of diameter at breast height values of survivors revealed a positive autocorrelation: larger trees tend to have large neighbours and smaller trees have small ones. These results suggest a model of differential mortality in which the smaller individuals in a stand, particularly those surrounded by larger individuals, are most likely to die over a given time interval.
Architecture et stratégies adaptatives des rejets de recépage du Buddleia variabilis
Authors: Phelouzat R. , Levacher P. , Chabot-Jacquety Y.
Published: September 2008

Cutting down close the stalks of Buddleia in February has resulted in an immediate development of populations of offshoots. Most of them would flower before the year was out. All of them, even those that remained vegetative, branched out and the branching showed mesotonous dominance. This was expressed, in the median zone, as a more pronounced increase in length of only one of the two branches at each node (stronger branch) rather than as an increase in leaf production. Reproductive branches are strong energy consumers; actually, they combine r strategy (seed production) with K strategy (pronounced cauline growth for space occupancy). Vegetative branches, weak energy consumers on which, however, leaves are particularly abundant, might serve as suppliers of metabolites. A nutritional equilibrium is perhaps achieved in a similar manner at the level of the stumps by the division of physiological roles between vegetative and reproductive offshoots. [Journal translation]
Coniferin, a biochemical indicator of commitment to tracheid differentiation in conifers
Authors: Savidge Rodney Arthur
Published: September 2008

Endogenous E-coniferin was characterized chemically and found to accumulate in cambia of Picea glauca, Pinus banksiana, Pinus strobus, and Larix laricina at the time of resumption of springtime cell-division activity and well before the initiation of lignification in differentiating tracheids. Coniferin content, quantified by high performance liquid chromatography, was highest on the centripetal side of the cambium, in developing xylem, at time of radial expansion of cambial derivatives. Stem ringing resulted in coniferin accumulation above the ring and disappearance below the ring. Coniferin was absent from leaves and dormant cambia. Exogenous coniferin was metabolized rapidly by in vitro cultures of P. strobus cambium grown on a defined medium containing the auxins 1-naphthalene acetic acid and indol-3-yl acetic acid and the cytokinin benzylaminopurine. The evidence suggests coniferin content of the cambium will be of practical value for determining commitment to and competence for wood formation in conifers.
Ultrastructure of organic acid secreting trichomes of chickpea (Cicer arietinum)
Authors: Lazzaro Mark D. , Thomson William W.
Published: September 2008

The acid-secreting trichomes of chickpea (Cicer arietinum L.) were composed of 18 cells, including 1 basal cell, 3 elongate stalk cells, and 14 head cells. A subcuticular secretion chamber with cuticular pores was present above the head cells at the trichome tip. The basal and stalk cells had large central vacuoles, endoplasmic reticulum, mitochondria, and small vacuoles. In the stalk cells, these small vacuoles were aligned along microtubles extending from the bottom to the top of the cells. Head cells had more dense cytoplasm than stalk cells and also had numerous mitochondria and small vacuoles. A labyrinth of tubules and vesicles at the edges of the head cells contained granular material similar to that observed in the extraplasmic space of the head cell and in the secretion chamber. In older head cells, the tubules were thinner and lacked granular material, the cells contained sequestering membranes and vacuoles, and calcium oxalate crystals were observed in the extraplasmic space. Plasmodesmata were not observed between the basal cell and the surrounding mesophyll cells, although numerous plasmodesmata with associated desmotubules and endoplasmic reticulum connected the trichome cells. Chloroplasts were not observed in the head or stalk cells, whereas the basal cell had small chloroplasts with reduced thylakoid networks and the mesophyll cells had large chloroplasts with well-developed thylakoids that may provide the fixed carbon for organic-acid secretion.
Effects of long-term elevated atmospheric CO2 concentration on Lolium perenne and Trifolium repens canopies in the course of a terminal drought stress period
Authors: Nijs I. , Impens I. , Behaeghe T.
Published: September 2008

A terminal drought stress regime was imposed on vegetatively fully developed Lolium perenne L. cv. Vigor and Trifolium repens L. cv. Blanca canopies in semicontrolled growth chambers that provided a high (626 ± 50 μL∙L−1) and an ambient (358 ± 35 μL∙L−1) CO2 growth environment. The chambers served as measurement units in an open system for continuous CO2 and water vapour exchange assessment. When stress was building up, high CO2 increased the ratio of real to potential canopy evapotranspiration in both species, thus reducing the higher potential rates that are generally observed in high CO2 under unstressed conditions towards the level of the ambient CO2 stands, without immediately affecting the net higher CO2 exchange rates that characterize the high CO2 treatment. Lolium perenne is more sensitive to drought stress in its initial response and divides the available amount of water more proportionally over the stress period than Trifolium repens. Water-use efficiency is roughly doubled and is affected later by drought stress in high CO2 for both species. It is concluded that long-term high CO2 treatment favours the survival of the species examined when exposed to severe, rapidly developing drought stress.
Organization of the Niagara Escarpment cliff community
Authors: Larson D. W. , Spring S. H. , Matthes-Sears U. , Bartlett R. M.
Published: September 2008

A sparse coniferous forest occurs on exposed cliff faces of the Niagara Escarpment in Southern Ontario. This paper presents the first quantitative study of the organization of the vegetation in these areas. The large-scale features of the Niagara Escarpment cliff community have been quantitatively analyzed, and a formal description is given of the changes in the physical and biological environments across the gradient from the plateau at the top of the cliff to the talus at its base. There were marked changes in soil depth, available photosynthetically active radiation, species richness, local diversity, and life-form characteristics across the gradient. Similar discontinuites in abundance were found for the most abundant species. Scatterplots and correlation analyses showed strong relationships between abundance and the two environmental factors, soil depth and available photosynthetically active radiation; however, these relationships were found mainly for those species present on the plateau at the top of the cliff. These results suggest that while resource pool size might influence species distribution on the plateau, other factors such as competitive displacement and disturbance seem to regulate the abundance of species in the talus and on the cliff face.