bluuebunny/crossref_metadata_2025 huggingface dataset:
Plant determined ineffective nodules in alfalfa (Medicago sativa): structural and biochemical comparisons
Authors: Vance C. P. , Johnson L. E. B.
Published: April 2008

Nodule structure, nodule enzymes of ammonia assimilation, nodule phosphoenolpyruvate carboxylase, nitrogenase-dependent acetylene reduction, and soluble protein were studied in four plant-determined ineffective genotypes and in one effective genotype of alfalfa (Medicago sativa L.) grown in a glasshouse. Ineffective nodules that formed on genotypes MnAg(In) and MnSa(In) were similar to effective nodules in early development. However, these nodules had smaller bacteroids and senesced much more rapidly than effective nodules. In contrast, nodules that formed on ineffective genotypes MnNC-3226(In) and MnNC-3811(In) were tumorlike and had few infection threads and bacteroids, and host cells were filled with starch. Nodules from plant-determined ineffective genotypes had reduced glutamine synthetase, glutamate synthase, phosphoenolpyruvate carboxylase, and nodule soluble protein when compared with effective nodules. There were differences between genotypes for all biochemical parameters assayed.
Sea ice diatoms from Manitounuk Sound, southeastern Hudson Bay (Quebec, Canada). III. Cymbellaceae, Entomoneidaceae, Gomphonemataceae, and Nitzschiaceae
Authors: Poulin Michel , Cardinal André
Published: April 2008

Four families of diatoms, well represented in the ice microflora of Manitounuk Sound, Hudson Bay, are treated. The Entomoneidaceae (Entomoneis, 6 taxa; Plagiotropis, 2 taxa) and the Nitzschiaceae (Nitzschia, 12 taxa) have more representatives than the Cymbellaceae (Amphora, 1 taxon) and the Gomphonemataceae (Gomphonema, 2 taxa). Taxonomic information is given for these 23 taxa by means of complete illustrated descriptions. One species and one variety are described as new in the genus Nitzschia, and new nomenclatural combinations are proposed for the six taxa of Entomoneis and the two of Plagiotropis.
Pericolporate pollen in Gentianaceae
Authors: Rao K. Sankara , Chinnappa C. C.
Published: April 2008

Pollen of six species of Centaurium Hill. (Gentianaceae) was examined by photon and scanning electron microscope. Significant variation in pollen morphology occurs in all the taxa. Pericolporate pollen encountered in C. pulchellum, C. littorale ssp. littorale, and C. exaltatum is reported. The derivation of the pericolporate type of pollen from the tricolporate type in the genus is demonstrated.
Studies on the mycoflora and its control on the seeds of some forest trees. I. Cedrus deodara
Authors: Mittal R. K.
Published: April 2008

By tests using standard moist blotters, potato–dextrose–agar plates, and moist sterilized sand, 26 fungal species belonging to 13 genera were isolated from seeds of Cedrus deodara Loud. Most of these fungi were present on seed surfaces and only nine caused deep-seated internal infections. Some of the more common species in different tests were Aspergillus flavus, A. luchuensis, Epicoccum purpurascens, Fusarium moniliforme, Pénicillium canadense, and Rhizopus oryzae. Aspergillus flavus, Penicillium canadense, and Rhizopus oryzae showed differences in pathogenicity to seed germination and seedling development in sterilized and unsterilized soils. Of the nine fungicides tested for the control of the seed-borne fungi, RH-2161, a liquid fungicide, was found to be the most effective. Dithane M-45 was also effective, whereas the remaining seven fungicides were less effective.
Experimental studies on some observed variations in Luffa aegyptiaca
Authors: Okusanya Olubukanla T.
Published: April 2008

The causes of some observed variations in plant size and leaf morphology of populations of Luffa aegyptiaca were investigated experimentally. The effects of soil type, soil salinity, soil moisture content, and mineral nutrients on the germination and growth of this species were examined. The results indicate that variations in size and leaf morphology between the population groups earlier described probably were caused by variations in soil type and soil nutrients. Nitrate was responsible for variation in leaf colour, potassium for leaf invagination, and phosphorus and nitrate together for leaf texture. Nitrate also played a major role in the variation in leaf size while calcium played a subsidiary role. Within a single population, variations would possibly also be caused by differences in soil conditions, principally humus content, soil moisture content, and salinity. The wide adaptability exhibited by this species also helps to explain its distribution on a wide range of soils.
Variable photosynthesis/photorespiration ratios in Hydrilla and other submersed aquatic macrophyte species
Authors: Holaday A. Scott , Salvucci Michael E. , Bowes George
Published: April 2008

Hydrilla verticillata plants collected from Orange Lake in Florida during the summer exhibited higher net photosynthetic rates and lower photorespiratory and dark respiratory rates than plants collected during the winter when measured at a standard temperature of 25 °C. Similar seasonal shifts in the CO2 compensation point, ranging from 17 μL CO2/L in summer to 90 in winter, occurred in Hydrilla from three geographically distinct lakes in Florida. Incubation of Hydrilla and five other submersed angiosperms under a high temperature (27 °C day) and long photoperiod (14 h) reduced the CO2 compensation point to less than 20. A continuously high CO2 concentration of 5000 μL/L (gas phase) prevented the decline in the CO2 compensation point, whereas 300 μL/L induced it. Lake-grown and chamber-grown Hydrilla with low photorespiratory capacity, as determined by low CO2 compensation points, showed elevated phosphoenolpyruvate carboxylase activity (239 versus 33 μmol/mg Chl per hour). Diurnal gas-exchange measurements at 300 and 3000 μL CO2/L (gas phase) demonstrated that low photorespiration Hydrilla exhibited net CO2 fixation in the dark at the higher CO2 level, probably via the elevated phosphoenolpyruvate carboxylase activity. Only Hydrilla with low CO2 compensation points exhibited net dark fixation and then only during the night period. The excretion of 14C-organic compounds was only 3% of the 14CO2 light fixation rate and thus too low to account for the reduced photorespiration. The potential to alter the photosynthesis/photorespiration ratio appears ubiquitous among submersed freshwater macrophytes. This ratio change to a low photorespiratory capacity, and the induction of a dark fixation capacity, would aid the carbon economy under summer daytime conditions of low inorganic carbon and high O2, where photorespiratory CO2 loss would otherwise be substantial.
Allelopathic effects of Engelmann spruce bark stilbenes and tannin–stilbene combinations on seed germination and seedling growth of selected conifers
Authors: Taylor Ronald J. , Shaw David C.
Published: April 2008

The allelopathic effects of Engelmann spruce bark and bark extacts on seed germination and seedling growth of several conifer species were examined. Extracts were hydroxystilbenes (isorhapontin and astringin) and condensed tannins. Experiments included the following: (i) seed germination in petri dishes with various concentrations of stilbenes and tannin–stilbenes; (ii) seed germination in petri dishes containing Engelmann spruce bark fragments; (iii) seedling growth in varying mixtures of peat/Engelmann spruce bark, the latter added either before or after seedling establishment; (iv) seedling growth in samples of Engelmann spruce forest soil horizons. In all experiments and in all species there was an allelopathic response to bark extracts. This response was expressed through inhibition of seed germination (seed-coat rupture and radicle emergence), necrotic discoloration and protoplasmic disruption of root-tip cells, suppression of root hairs, and repressed growth in general. Among the conifers tested Pinus ponderosa and Tsuga mertensiana appeared to be the most tolerant to bark extracts, Pinus contorta the most sensitive. Picea engelmannii was moderately sensitive.
Demographic study of the macrothallus of Leathesia difformis (Phaeophyta) in Nova Scotia
Authors: Chapman A. R. O. , Goudey C. L.
Published: April 2008

A population of Leathesia difformis macrothalli was examined by actuarial analysis. Plants were present for only 12 weeks between mid-June and early September. During that time, increasing mortality rate was correlated with increased crowding. Experimental reduction of crowding markedly reduced mortality rates. Mortality rate was also correlated with wave motion. Leathesia difformis grew epiphytically on Chondrus crispus and Corallina officinalis. Mortality rates were not significantly affected by host species type. Harvesting of biomass increments and knowledge of mortality rates allowed estimation of net production by the L. difformis population as 17 mg C∙m−2∙day−1.
Notes on the taxonomy and nomenclature of Festuca occidentalis and F. idahoensis
Authors: Pavlick Leon E.
Published: April 2008

Festuca occidentalis occurs in open forests and glades, always in at least partial shade. In British Columbia it occurs from the U.S.A. border to about latitude 57° N. It has leaf structure, panicle structure, spikelet length, glume length, lemma length, lemma scabrosity, awn length, anther length, and ovary vestiture which are different from F. idahoensis. Festuca idahoensis is found in grasslands (including subalpine meadows) and in openings in dry forests bordering grasslands, always in open, nonshaded situations. In British Columbia it occurs from the U.S.A. border northward to about 51° N. Despite the recent lumping of these two taxa, morphological and ecological evidence strongly suggests that they should be treated as separate species.
Influence de la variété de Vigna unguiculata dans l'expression de trois associations endomycorhiziennes à vésicules et arbuscules
Authors: Ollivier B. , Bertheau Y. , Diem H. G. , Gianinazzi-Pearson V.
Published: April 2008

Vesicular–arbuscular (VA) mycorrhizas formed by Glomus E3, G. mosseae, and G. epigaeus have been studied in two cultivars of Vigna unguiculata L. Walp. (58-185 and Bambey 30). Glomus mosseae and Glomus E3 stimulated the growth of both cultivars while G. epigaeus only gave a positive growth effect with the cultivar 58-185. With G. epigaeus, infection levels were lower and growth effects smaller than with the other VA fungi. Growth stimulations were accompanied by the appearance of additional soluble alkaline phosphatases in extracts of mycorrhizal roots. The number and the electrophoretic mobility of these enzymes varied depending on the VA fungus involved, suggesting that they were of fungal origin.
Flora of Alberta: Sparganium angustifolium and Erigeron trifidus
Authors: Packer John G.
Published: April 2008

Evidence is presented to justify two taxonomic treatments that appear in the revised Flora of Alberta. They are the inclusion of Sparganium emersum Rehm. (S. multipedunculatum (Morong) Rydb.) and Sparganium chlorocarpum Rydb. in Sparganium angustifolium Michx. and the recognition of Erigeron trifidus Hook. as a distinct species.
Occurrence of patatin during growth and storage of potato tubers
Authors: Racusen David
Published: April 2008

The glycoprotein patatin comprises more than 20% of the soluble protein in mature potato tubers. To determine patatin content during development, tubers of cv. Kennebec were field-planted and analyzed during the growing season. No change in patatin content (based on dry weight) was seen in tubers weighing 2 g after 43 days compared with tubers weighing 200 g at harvest (125 days). Patatin content relative to other soluble protein constituents did not change during storage at 4 °C for 127 days. Patatin (and general protein) content was lowest when tubers sprouted after 219 days of storage. Patatin was detected in the leaves and stems of potato plants.
An assessment of spruce growth response specificity after inoculation with coexistent rhizosphere bacteria
Authors: O'Neill G. A. , Chanway C. P. , Axelrood P. E. , Radley R. A. , Holl F. B.
Published: April 2008

The influence of inoculation with rhizosphere bacteria on hybrid spruce (Picea glauca × engelmannii) seedling growth was investigated by isolating bacteria from the rhizosphere of naturally regenerating spruce seedlings collected from two ecologically distinct zones of British Columbia. Forty bacterial strains from spruce were screened in a seedling growth experiment, and several strains were shown to stimulate spruce seedling growth. The three most effective spruce growth promoting strains from each ecological zone were then tested in a seedling growth response specificity experiment in which seed, soil, and bacteria from both spruce ecosystems were examined in all possible treatment combinations, including pasteurized soil. Spruce seedling growth was primarily affected by seed and soil source (Salmon Arm > Mackenzie for both factors), and by soil pasteurization (pasteurized > unpasteurized). Significant growth effects due to bacterial treatment in the specificity experiment occurred only in pasteurized soil, but seedling biomass accumulation was stimulated by up to 59% in response to inoculation. There was no evidence of growth response specificity that was related to plant – bacteria adaptation within spruce ecotypes; two of the Mackenzie bacterial strains significantly inhibited growth of Mackenzie seedlings in Mackenzie soil, but two strains stimulated the growth of Salmon Arm seedlings, one in each soil type. Two Salmon Arm strains significantly stimulated growth of Mackenzie seedlings on Salmon Arm soil, and two strains stimulated the growth of Salmon Arm seedlings, one in each soil type. Seedling biomass was greater when treatments of spruce seed, soil, and rhizosphere bacteria that originated from the same geographic site were pooled and compared with treatments in which at least one factor originated from the other site. However, this effect was explained by the significant seed × soil interaction in the absence of bacteria; mean seedling biomass was greatest when spruce seed and soil treatments with the same geographic origin were pooled and compared with unrelated seed – soil combinations. Seedlings from pooled treatments were also significantly larger when bacteria and soil had a common geographic origin, but only when tested in pasteurized soil. Our results indicate that spruce growth promoting rhizosphere bacteria can be isolated from naturally regenerating spruce seedlings, but growth response variability was observed between trials. Seedling growth promotion by bacterial strains was not related to the use of spruce ecotypes, soil, and (or) rhizosphere bacteria with a common geographic origin. Key words: spruce seedlings, growth, inoculation, rhizosphere bacteria.
Germination response patterns to temperature during afterripening of achenes of four Texas winter annual Asteraceae
Authors: Baskin Carol C. , Baskin Jerry M. , Auken O. W. Van
Published: April 2008

Patterns of change in temperature requirements for germination of achenes of four Texas winter annual Asteraceae were investigated as they afterripened at simulated summer habitat temperatures. In addition, temperature requirements for after-ripening were determined. In Gaillardia pulchella, Krigia gracilis, and Pyrrhopappus multicaulis, the maximum temperature for germination increased during afterripening (type 1 response pattern). This is the first report of a type 1 pattern in the Asteraceae. In Hymenoxys linearifolia, the maximum and minimum temperatures for germination increased and decreased, respectively, increasing to two the number of winter annuals with a type 3 response pattern. As in winter annuals in other plant families, achenes of the four species required exposure to moderately high temperatures (25:15, 30:15 °C) to gain the ability to germinate to high percentages at autumn temperatures in autumn. Of the 32 species of Asteraceae whose afterripening pattern has been investigated, 3 have type 1, 22 have type 2, and 7 have type 3. Evidence suggests that types 1 and 3 and types 2 and 3 are more closely related physiologically than are types 1 and 2. Key words: winter annuals, Asteraceae, achenes, seed germination, afterripening.
Cellulose mass loss in ombrotrophic bogs of northeastern North America
Authors: Santelmann Mary V.
Published: April 2008

Profiles of cellulose mass loss were measured for six Sphagnum bogs in eastern North America as an index of decomposition rates. After 2 years, mass loss rates in the upper 5 cm of the profiles averaged 49% in hummocks, 52% in hollows where the water table was more than 5 cm below the surface, and 21% in hollows where the water table was within 5 cm of the surface. Hummock profiles were of three types: (i) mass loss highest at the surface, gradually decreasing to very low rates below the water table; (ii) mass loss highest at the surface, decreasing for 10 – 20 cm, with a second peak in the region of the water table; and (iii) mass loss low at the surface with a subsurface peak. Mass loss rates for all profiles reached minimum values below the water table, averaging 3% in hummocks and 5% in hollows after 2 years. Cellulose mass loss was quite variable in upper portions of the profiles; within-site variance was almost as great as between-site variance, reflecting similarity among these bogs and heterogeneity within each site. Analysis of variance of mass loss at the hummock surface showed no significant effect of site; however, contrasts among means showed that mass loss rates at the surface of hummocks of the northern (Newfoundland) bogs were significantly lower (p < 0.05) than those from the sites farthest south (in Nova Scotia and Maine). Key words: cellulose mass loss, Sphagnum bog, decomposition.
Ovary structure and anatomy in the Heliconiaceae and Musaceae (Zingiberales)
Authors: Kirchoff Bruce K.
Published: April 2008

Ovary anatomy and organography was investigated in five species of Heliconia (Heliconiaceae) and three species of Musa (Musaceae). The ovaries of both genera may be longitudinally divided into three regions: sublocular, locular, and prolongation. The prolongation is the elongated closure of the top of the locules. The proportions of these regions differ between genera and to a lesser extent among species within a genus. In general, Heliconia has a larger sublocular region while the prolongation is larger in Musa. These differences are correlated with the occurrence of gynopleural nectaries in the sublocular region of the Heliconiaceae and in the prolongation of the Musaceae. Anatomical and organographic details are related to our knowledge of the development of the ovary and fruit. Many anatomical differences between the genera are correlated with the functions of these regions in the fruit. The structure and homology of the placental trichomes of the Musaceae are discussed, and I conclude that they are not homologous to the arils of the other Zingiberales. Key words: plant morphology, plant anatomy, nectaries, monocotyledons.
Biosystématique du complexe de l’Aster novi-belgii (Asteraceae: Astereae) au Québec
Authors: Labrecque Jacques , Brouillet Luc
Published: April 2008

The Aster novi-belgii L. complex is one of the least understood groups of this genus in Quebec. The goal of this study is to better circumscribe the taxa often confused with it (A. puniceus and A. anticostensis), to determine whether species described within the complex are valid (A. "foliaceus", A. johannensis, etc.), and to establish their habitat and distribution. Samples were collected throughout the range of the species in Quebec. Aster novi-belgii var. novi-belgii and A. novi-belgii var. crenifolius individuals are 2n = 6x = 48; a count of 2n = 80 is reported for A. "longifolius''. A morphometric analysis using principal components and discriminant analyses shows that A. novi-belgii is easily distinguished from A. puniceus and A. anticostensis. No segregate species can be recognized within the A. novi-belgii complex. However, at the infraspecific level, two varieties seem recognizable: a coastal, robust morphotype in the Gaspé Peninsula (A. novi-belgii var. crenifolius), and a strongly pubescent form (A. novi-belgii var. villicaulis) on the Saint-Jean and Restigouche rivers. The new combination A. novi-belgii L. var. crenifolius (Fern.) Labrecque & Brouillet is proposed. Keywords: Asteraceae, Aster, biosystematics, Quebec, morphometry.
The separation of Eleocharis obtusa and Eleocharis ovata (Cyperaceae) in eastern Canada
Authors: Larson B. M. H. , Catling P. M.
Published: April 2008

Eleocharis obtusa and Eleocharis ovata are recognized as distinct species or combined in recent taxonomic literature. To assess their morphological relationship and to evaluate all morphological characters potentially useful for their separation, 11 floral and achene characters were measured on 130 eastern Canadian herbarium specimens. Tubercle width was bimodally distributed and completely separated groups established on the basis of stamen number: plants referable to E. ovata had tubercles less than 0.5 mm wide and two stamens, whereas plants referable to E. obtusa had tubercles greater than 0.5 mm wide and three stamens. Since determination of stamen number requires dissection under a microscope and tubercle width requires accurate measurement, the most readily utilized character was found to be the ratio of tubercle width to achene width, which can be measured or estimated. The tubercle was less than 2/3 the width of the achene in E. ovata and more than 2/3 in E. obtusa. Differences in these characters were associated with significant but less dramatic differences in other characters, suggesting that the two taxa should be treated as distinct species. Keywords: Eleocharis obtusa, Eleocharis ovata, Cyperaceae, taxonomy, classification, Canada.
Aquatic heterophylly as a survival strategy in Melaleuca quinquenervia (Myrtaceae)
Authors: Lockhart Christine S.
Published: April 2008

The broad-leaf paper bark or melaleuca tree (Melaleuca quinquenervia (Cav.) Blake) is an emergent, semiaquatic tree whose morphological plasticity allows it to invade wetland and terrestrial habitats. While studying the effect of hydroperiod on melaleuca seedlings, two types of aquatic leaf forms were observed under submersed conditions. Linear leaves developed at least 9.5 cm below the water surface and were associated with short internodes. Short, broad, incurved transitional leaves formed as the seedlings approached the water surface. Aerial leaves were flat and spatulate to oblanceolate. Leaf length to width ratios, stomatal density, and shoot internode lengths were significantly different between the three leaf forms. Characteristics of submersed melaleuca seedlings are similar to those of other aquatic heterophyllic plants that grow in areas where water levels fluctuate. An increased understanding of morphological variations of this invasive tree may lead to additional control methods and mechanisms. Keywords: Melaleuca, aquatic, heterophylly.
Relationship of mycorrhizal activity to time following reclamation of surface mine land in western Kentucky. I. Propagule and spore population densities
Authors: Gould Ann B. , Hendrix James W. , Ferriss Richard S.
Published: April 2008

The relationships between estimates of mycorrhizal activity, time following reclamation, and soil edaphic factors were investigated over a period of 2.5 years during reclamation of five abandoned surface mine sites in western Kentucky. These sites were reclaimed at different times and were in varying stages of revegetation. At the seeding stage of reclamation and soon thereafter, propagule and spore population densities were low but invariably present. Roots recovered from minespoil during this period were not colonized, and colonization was not observed until a full year following reclamation. During the first 2 years following reclamation, colonization of roots, population densities of propagules and spores, and total spore volume increased rapidly. Thereafter, vegetative and mycorrhizal parameters appeared to stabilize. Each estimate of mycorrhizal activity in minespoil was highly correlated with time following reclamation and all other mycorrhizal parameters. Edaphic factors with positive relationships to mycorrhizal propagule and spore population densities included soil organic matter and calcium. Keywords: Glomales mycorrhizal fungi, reclamation, abandoned minespoil, most probable number, propagule population density.
Pollination biology of yellow starthistle (Centaurea solstitialis) in California
Authors: Maddox D. M. , Mayfield A. , Joley D. B. , Supkoff D. M.
Published: April 2008

Various facets of the pollination biology affecting achene production of Centaurea solstitialis L. were examined. Production of viable achenes commenced in capitula bagged or excised in the late flowering stage (F-2 midstage). In all studies in which capitula were prevented from crossing, only one plant had a high level of achene production, all others producing either a few achenes or none at all. Achene production in plants allowed to cross was high and significantly greater than in plants prevented from crossing. Persistent low levels of self-fertilization in most plants indicated that there was selection against inbreeding. The pollen presentation mechanism for C. solstitialis was similar to that of other Centaurea spp. described previously. The most commonly observed insect visitors of yellow starthistle capitula were Hymenoptera spp., especially the European honeybee. Keywords: Centaurea, pollination, yellow starthistle.
Cytological and molecular analysis of annual species of the genusMedicago
Authors: Mariani A. , Pupilli F. , Calderini O.
Published: April 2008

Medicago rugosa and M. scutellata, two annual species of the genus Medicago, have aroused considerable interest because they carry useful traits that could be introduced into alfalfa and have a chromosome number (2n = 30) that is quite unusual in Medicago. A cytogenetic and molecular study was undertaken to investigate the annual diploid species with 2n = 16 and 2n = 14 that seem to be the most closely related to M. rugosa and M. scutellata, with the aim of characterizing these diploid species and determining their genetic relationship with the species with 2n = 30. Karyological analysis established that some of the diploid species investigated were more similar than the others to both M. rugosa and M. scutellata (as in the case of M. intertexta, M. rotata, and M. polymorpha) or at least to one of those two species (as was the case with M. doliata, M. muricoleptis, and M. murex). RFLP analysis identified four species, namely M. intertexta and M. muricoleptis with 2n = 16, and M. polymorpha and M. murex with 2n = 14, as having the highest degree of genetic affinity with the two species with 30 chromosomes. These findings suggest the possibility of identifying the ancestors of M. rugosa and M. scutellata among those four species and therefore of verifying the probable allopolyploid origin of the two species in question. Keywords: Medicago, annual species, karyotypes, RFLPs.
No difference in leaf respiration rates among temperate, subarctic, and arctic species grown under controlled conditions
Authors: Collier Donald E.
Published: April 2008

To test the theory that leaf respiration rates are inherently higher in arctic species compared with temperate species, a total of 35 species from temperate, subarctic, and arctic locations were grown under controlled conditions and leaf respiration rates were measured. Regardless of growth temperature (either 10 or 20 °C), leaf respiration rates measured at the growth temperature were independent of a species' geographic origin. In addition, salicylhydroxamic acid inhibited the alternative oxidase equally in all groups of species. Acclimation of leaf respiration to temperature was observed in all three geographic plant groups, i.e., leaf respiration rates of 20 °C-grown plants were not significantly different than rates of 10 °C-grown plants when respiration was measured at the growth temperature. These results suggest that arctic species do not have inherently high leaf respiration rates, higher alternative pathway respiration, or greater temperature acclimation ability compared with temperate species. Keywords: alternative pathway respiration, arctic, leaf respiration, subarctic, temperate, temperature.
A persistent seed bank of the bull thistle Cirsium vulgare
Authors: Doucet Colleen , Cavers Paul B.
Published: April 2008

Seeds of Cirsium vulgare were collected from two populations in southwestern Ontario and stored at the site of collection at three depths in the soil. After intervals of 6 to 30 months, seed samples were extracted, the seeds classed as germinated, dead, or firm, and then the firm seeds were set to germinate in a growth cabinet. Both populations established a persistent seed bank when left at the 15 cm depth; however, most seeds do not get buried at great depths. After storage at the surface or 3 cm deep, seeds in an arable sandy soil did not persist beyond 6 months. In contrast, some seeds stored in shaded conditions in a clay loam soil maintained viability for 30 months at die surface and at 3 cm. In some cases, the germination rate of seeds was retarded after storage, especially for seeds that were extracted from soils subjected to wetting and drying before seed retrieval. A separate experiment confirmed that wetting and drying can delay the germination of some seeds of C. vulgare. Key words: seed bank, germination, seed wetting and drying, Cirsium vulgare, bull thistle.
Determination of allelopathic potential of a weed Pluchea lanceolata through a multifaceted approach
Authors: Inderjit Inderjit , Kaur Surinder , Dakshini K. M. M.
Published: April 2008

The allelopathic potential of soils from four sites infested with the weed Pluchea lanceolate (DC.) C.B. Clarke (Asteraceae) was investigated. All sites had similar precipitation, similar crops, and weeds in addition to P. lanceolata. The objectives of this study were threefold: first, variations in the allelopathic effects of P. lanceolata infested soils on growth of three crops; second, soil phenolic content as a result of P. lanceolata infestation; and third, if the chemical characteristics and mycoflora of soils and biotic characteristics of P. lanceolata are responsible for the differences in allelopathic potential. Allelopathic effects of P. lanceolata infested soils were assessed on seedling growth of onion, cucumber, and turnip. Qualitative variation in the soil phenolic content from the four P. lanceolata infested sites was observed. No significant differences in soil mycoflora, soil nutrients, and P. lanceolata biotic characteristics were observed. Growth experiments showed mat crops demonstrated variation in allelopathic response to the soils from the four P. lanceolata infested sites. The present study indicates mat in natural field conditions, allelopathic potential of P. lanceolata varies because of agricultural practices specific to each site. Keywords: allelopathy, Asteraceae, interference, phenolics, soil nutrients, weed.
Allocation of reproductive resources within inflorescences of Petrocoptis grandiflora (Caryophyllaceae)
Authors: Guitián Javier , Navarro Luis
Published: April 2008

Patterns of fruit set were studied in Petrocoptis grandiflora, a species endemic to the northwestern Iberian Peninsula. This plant has a dichasial inflorescence in which the central flower opens first, followed by first-order lateral flowers and then second-order lateral flowers. We investigated whether flowers at different positions in the inflorescence differ in duration, ovule number, nectar production, or probability of fruit set. Our results indicate that mean duration, ovule number, nectar volume, and probability of fruit set are higher for central than for lateral flowers. Fruit set was higher for central than for first-order lateral flowers, and higher for first- than for second-order lateral flowers. To investigate the effects of loss of the central flower, selected inflorescences were manually "decentred." For lateral flowers, analysis of variance indicated that fruit set was affected both by flower position in the inflorescence and by decentring. However, neither total inflorescence fruit set nor mean duration of flowers in the inflorescence differed significantly between decentred and untreated inflorescences. These results suggest that the observed pattern of fruit set in this species is a result of within-inflorescence competition for the limited amount of resources available for fruit production, and that these resources may be redistributed in response to damage to flowers within the inflorescence. Inflorescences of P. grandiflora can thus be considered to act as semi-autonomous units with regard to resource allocation. Keywords: inflorescences, fruit set, resource allocation, Petrocoptis grandiflora.
Mycorrhizal chronosequence near Exit Glacier, Alaska
Authors: Helm D.J. , Allen E.B. , Trappe J.M.
Published: April 2008

Mycorrhizal fungi associated with plant species may change as vegetation develops following disturbance. The objectives of this study were to compare ectomycorrhizae through a chronosequence on deglaciated land from bare mineral soil to mature forest and to determine time required for mycorrhizal formation on natural seedlings. A chronosequence that formed as Exit Glacier retreated enabled us to document changes in mycorrhizae on existing woody plants, including Populus balsamifera ssp. trichocarpa (Torr. & Gray) Hult, (black cottonwood) that dominates the early stages, Alnus sinuata (Regel) Rydb. (Sitka alder) that has few ectomycorrhizal fungal associates, and Picea sitchensis (Bong.) Carr. (Sitka spruce) that typifies late successional stages. Some seedlings of Populus balsamifera became ectomycorrhizal within 3 weeks of germination but most took longer. Although a dark type without clamp connections dominated willows in the second and third stage, it was not a dominant in the first stage and was rare on 1st year seedlings. Ectomycorrhizal types differed among successional stages for Populus balsamifera. Diversity increased from early successional stages to later stages, mostly from an increase in evenness rather than richness. Arbuscular mycorrhizae were not found on any woody plants, although a few herbaceous plants had low infection percentages. Keywords: ectomycorrhizae, chronosequence, Populus, Alnus, Picea, Salix.
Le Clauzadella gordensis gen. et sp. nov., ascomycète lichénicole non lichénisé (Verrucariales, Verrucariaceae)
Authors: Navarro-Rosinés Perre , Roux Claude
Published: April 2008

Clauzadella gordensis Nav.-Ros. et Roux gen. et sp. nov., a parasymbiont ascomycete on Verrucaria viridula, differs from species in the genus Stigmidium by its obviously bigger ascomata, periphyses, and asci, thicker, violet tinged ascoma wall, distinct ostiolar channel, and triseptate mature ascospores. Clauzadella differs from typical members of the Verrucariaceae only by its scarce, inamyloid hymenial gelatine. The genus, as well as Stigmidium, is considered to belong to the family Verrucariaceae (Verrucariales). Keywords: lichenicolous ascomycete, Verrucariaceae, Clauzadella, morphology, structure, systematics.
Intercellular pectic protuberances in leaves of some Xyris species (Xyridaceae)
Authors: Machado S.R. , Sajo M. G.
Published: April 2008

Mature leaves of eight species of Xyris were prepared by standard methods for electron transmission microscopy. Wartlike intercellular pectic protuberances were observed on the surface of inner periclinal walls of epidermal cells in Xyris obcordata, Xyris hymenachne, and Xyris pterygoblephara. In the latter, the protuberances also occur on the surface of parenchymatic mesophyll cells; they frequently project into intercellular spaces and may connect opposing cells. For the genus Xyris, the intercellular pectic protuberances may be considered taxonomically significant at the species level. Keywords: Xyris, Xyridaceae, pectin, cell wall.
Inelastic performance of screw-connected cold-formed steel strap-braced walls
Authors: Al-Kharat M. , Rogers C. A.
Published: April 2008

Cold-formed steel, screw-connected strap-braced walls (15 specimens, 2.44 m × 2.44 m each), designed following a capacity-based approach, were tested to evaluate their performance in the inelastic range of behaviour. Gross cross-section yielding of the tension braces was the specified failure mode in the design procedure. Extended tracks and additional shear anchors were installed, such that inelastic deformations would be limited to tension yielding of the braces. Walls without extended tracks were able to reach their yield level; however, damage to other frame elements occurred, thus reducing the ductility level that was attained. Cyclically loaded walls (0.5 Hz) with track extensions showed that wall performance is also dependent on the strain rate experienced by the braces. An Fu / Fy ratio greater than 1.2 is necessary to limit the possibility of brace fracture under seismic loading. Preliminary force modification factors, Rd = 2.0 and Ro = 1.3, are recommended for walls designed and detailed to achieve ductile performance.
Neural-network-based damage classification of bridge infrastructure using texture analysis
Authors: Kabir Shahid , Rivard Patrice , Ballivy Gérard
Published: April 2008

Damage in concrete structures can be assessed by analyzing the texture of surface deterioration using optical concrete imagery. This research proposes the application of an enhanced method of texture analysis, based on the signal processing technique of Haar’s wavelet transform in combination with the grey level co-occurrence matrix statistical approach, to characterize and quantify damage. Three different types of imagery, colour, greyscale, and thermography are evaluated for their effectiveness in representing surface deterioration. The multilayer perceptron artificial neural network classifier is applied on three different datasets: spatial, spectral, and a combination spatial–spectral dataset. Results show that the combination of textural and spectral data produced the highest overall accuracies; the thermography provided better classifications than the other types of imagery. Classifications based on the combination datasets were used to determine the different levels of damage in the concrete.
Thermal effect on fiber reinforced polymer reinforced concrete slabs
Authors: Zaidi A. , Masmoudi R.
Published: April 2008

The difference between the transverse coefficients of thermal expansion of fiber reinforced polymer (FRP) bars and concrete generates radial pressure at the FRP bar – concrete interface, which induces tensile stresses within the concrete under temperature increase and, eventually, failure of the concrete cover if the confining action of concrete is insufficient. This paper presents the results of an experimental study to investigate the thermal effect on the behaviour of FRP bars and concrete cover, using concrete slab specimens reinforced with glass FRP bars and subjected to thermal loading from –30 to +80 °C. The experimental results show that failure of concrete cover was produced at temperatures varying between +50 and +60 °C for slabs having a ratio of concrete cover thickness to FRP bar diameter (c/db) less than or equal to 1.4. A ratio of c/db greater than or equal to 1.6 seems to be sufficient to avoid splitting failure of concrete cover for concrete slabs subjected to high temperatures up to +80 °C. Also, the first cracks appear in concrete at the FRP bar – concrete interface at temperatures around +40 °C. Comparison between experimental and analytical results in terms of thermal loads and thermal strains is presented.
Lane-changing gap acceptance model for freeway merging in simulation
Authors: Kim Jin-Tae , Kim Joonhyon , Chang Myungsoon
Published: April 2008

Existing techniques for microscopic simulation of lane changes utilize a single critical gap for a single vehicle. Freeway merging areas have been among the most difficult aspects of simulations due to the wide variety of merging behaviors in these areas. This paper proposes a gap acceptance model developed to update the size of the critical trailing gap for a merging vehicle during simulation based on the location of the vehicle in an acceleration lane. It also considers the relative speed and critical leading gap. Sets of critical trailing gap values for various situations are computed. The outputs from the microscopic simulations utilizing the proposed model were compared with field data, producing strong statistical evidence that the simulation results and field data were significantly comparable.
Angular variations of K and L X-ray fluorescence cross sections for some lanthanides
Authors: Han I , Şahin M , Demir L
Published: April 2008

Kα, Kβ, Lα, and Lβ X-ray fluorescence cross sections for lanthanides in the atomic range 62 ≤ Z ≤ 68 (Sm, Eu, Gd Tb, Dy, Ho, and Er) were simultaneously measured by 59.54 keV incident photon energy at five angles ranging from 120° to 160°. The measurements were performed using an Am-241 radioisotope as the photon source and a Si(Li) detector. The Lα X-ray fluorescence cross section (σLα) was found to decrease with increasing emission angle and showed an anisotropic distribution of Lα X-rays. Kα, Kβ, and Lβ X-ray fluorescence cross sections (σKα, σKβ, and σLβ) were observed to be angle-independent and showed an isotropic distribution of Kα, Kβ, and Lβ X-rays. The Kα and Kβ X-rays originate from filling of the K shell (J = 1/2) vacancies, Lβ X-rays from filling of the L1 and L2 (J = 1/2) subshell vacancies, and Lα X-rays from filling of the L3 subshell (J = 3/2) vacancy. The fluorescent X-rays originating from the vacancy states with J = 1/2 are isotropic and unpolarized, but fluorescent X-rays originating from the vacancy states with J > 1/2 are anisotropic and polarized. Thus, the atomic inner shells vacancy states with J > 1/2 are aligned whereas vacancy states with J = 1/2 are not aligned. Lα fluorescence X-rays have an anisotropic distribution, while Kα, Kβ, and Lβ fluorescence X-rays have isotropic distribution. Furthermore, the IKβ/IKα, ILα/IKα}, ILβ/IKα, and ILβ/ILα intensity ratios for the elements under investigation were determined. The experimental cross sections and intensity ratios for Kα, Kβ, Lα, and Lβ fluorescence X-rays were also determined, and these experimental values were compared with our calculated theoretical values.PACS Nos.: 32.30.Rj, 32.80.Cy
Effect of film thickness on the physical properties of ZnO:Al thin films deposited using a spray pyrolysis technique
Authors: Rozati S M
Published: April 2008

ZnO:Al(ZAO) films with various amount of solution, in the range 10–120 mL, were prepared on a glass substrate. Deposition was carried out using a spray method, and the substrate temperature was held at 500 °C. It was found that increasing the amount of solution causes the ZnO:Al thin films to exhibit a strong orientation along (002). The variation in the structural properties due to variation in the volume of solution was investigated by means of X-ray diffraction. The lowest sheet resistance obtained was 40 Ω/cm2 for a 120 mL solution. PACS Nos.: 73.61.–r, 78.20.–e
Polarizability and hyperpolarizability of Li+ calculated from the DC-Stark shift
Authors: Themelis S I
Published: April 2008

We show how energy shifts induced by DC fields can be used to obtain the polarizability α and the hyperpolarizability γ of the Lithium cation efficiently. We employ a nonperturbative method to solve a complex eigenvalue matrix equation constructed in terms of two separately optimized function spaces, Q and P. The values obtained for α and γ are in excellent agreement with other elaborate theoretical calculations. PACS Nos.: 02.70.–c, 32.10.Dk, 32.60.+i, 42.65.An
Study of the frequency fluctuations of a semiconductor diode laser
Authors: Ray A
Published: April 2008

Frequency fluctuations of an inexpensive single-mode semiconductor diode laser, which operates in the 822 nm region, are investigated by direct measurement of the error signal. The linear slope of first derivative signal of a transition in the (2,1,1) vibration-rotation band of water vapour is used as a frequency discriminator. A balanced photodetector is used to reduce the intensity noise and to improve the S/N ratio. Frequency stability of the diode laser is investigated when the laser is under a free-running condition and is locked to the line center of the reference transition. An integrator is used to provide feedback voltage to the laser current driver. After frequency stabilization, a more than 60-fold improvement in long-term laser-frequency stability is attained over the performance provided by the free-running semiconductor diode laser. The frequency-noise power spectrum of the diode laser is extracted from the error signal for the Fourier-frequency range ~100 Hz. The Allan variance curve for the laser system is obtained from the frequency-noise power spectrum of the error signal by using a suitable mathematical relation under certain approximations. The extracted values of the Allan variance are compared with the theoretical τ–1 model. The experimental setup is easy to implement in graduate laboratory classes. PACS Nos.: 42.55.Px, 42.62.Fi, 33.70.Jg
Wave equations for antisymmetric multispinors
Authors: Maloomeh F Q , McKeon D.G.C.
Published: April 2008

The Bargmann–Wigner equations for a spin s field are of the form (iγ · ∂ + m)α1α′1 · ψα′1α2...α2s = ··· = (iγ · ∂ + m)α2sα′2s ψα1···α′2s = 0 where ψα1···α2s is totally symmetric in all spinor indices. We consider these wave equations for the case in which ψα1···α2s is totally antisymmetric in all indices, examining in particular the situations in which there are two or three indices.PACS No.: 03.65Pm
Hamiltonian, path integral, and BRST formulations of the Chern–Simons theory under appropriate gauge-fixing
Authors: Kulshreshtha U , Kulshreshtha D S
Published: April 2008

The Hamiltonian, path integral, and BRST formulations of the Chern–Simons theory in two-space one-time dimensions are investigated under appropriate gauge-fixing conditions.PACS Nos.: 11.10.Ef, 11.10.Kk, 12.20.Ds
A crash course on the simple Bethe Ansatz
Authors: Schmidt Jeffrey R
Published: April 2008

The simple Bethe Ansatz is illustrated step by step in great detail for a variety of many-body quantum problems and lattice models. The focus is on a constructive presentation in which the problems of determining the spectral conditions and full wave functions are completely and transparently solved for the cases of the isotropic Heisenberg chain, N bosons or spin ħ/2 fermions with δ-function interactions, the XX-Heisenberg chain, and the six-vertex model. PACS Nos.: 05.50.+q, 05.30.Fk, 03.65.Fd, 75.10.Hk, 71.10.Fd
Variation in amount of surrounding forest habitat influences the initial orientation of juvenile amphibians emigrating from breeding ponds
Authors: Walston Leroy J. , Mullin Stephen J.
Published: April 2008

Juvenile dispersal is important for the persistence of ​amphibian populations. Previous studies have observed nonrandom orientation in juvenile amphibians emigrating from breeding ponds; however, the environmental cues associated with these movements are not well understood. We examined the emigration behavior of recently metamorphosed juveniles of three pond-breeding amphibian species from three woodland ponds. We found that juvenile small-mouthed salamanders ( Ambystoma texanum (Matthes, 1855)), American toads ( Bufo americanus Holbrook, 1836), and wood frogs ( Rana sylvatica LeConte, 1825) exhibited nonrandom orientation upon exiting the breeding ponds. Furthermore, we found a positive relationship between captures of juvenile small-mouthed salamanders and wood frogs and width of the surrounding forest habitat, indicating that these species are selecting areas with broader forested habitat upon exiting the breeding ponds. Our results indicate that migrating juvenile amphibians may rely on direct environmental cues because the orientation of small-mouthed salamanders and wood frogs was influenced by width of the surrounding forested habitat. These observations support previous studies suggesting that maintaining forest habitat, along at least a portion of breeding ponds, is important for the persistence of amphibian populations.