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Theb ehavioro fpollen grainsw ithint he airspacea roundE phedrat rifurcais described.V ectoral analyses of pollen grains moving around stems and ovules indicate a complex pattern of directional and magnitudinal changes in trajectories that can be related to the geometries of surfaces that obstruct airflow. Pollen grains, passing around cylindrical stems oriented normal to the directiono f ambient airflow,a re deflectedi n circumrotatingn on-laminarf low-patterns. Stems tilted downwind deflect pollen grains into trajectories along leeward surfaces of stems. These trajectories travel acropetally in a spiraling pattern and may intersect airflow patterns created around and by ovules. Computer analyses of pollen motion...
The anomalous secondary wood of Atriplex confertifolia stems consists of vascular strands of xylem, phloem, and parenchyma embedded in fiberous conjunctive tissue. The included parenchyma contains chloroplasts and is capable of photosynthesis, as measured by 14CO2 uptake by wood in the light. Published in American Journal of Botany, volume 61, issue 5, on pages 444 - 448, in 1974.
The effects of inoculation with vesicular-arbuscular mycorrhizal fungi on nonmycotrophic (plants which do not form a mycorrhizal association) colonizing annuals and on mycotrophic perennials were investigated in southwestern Wyoming. A subsoil containing no initial mycorrhizal inoculum was used, and seeds of the later successional perennials were planted. The annuals were removed from one-half of the sampling quadrats to test for the interaction of competition and mycorrhizae on the perennials. During the third and fourth years of succession, the density and percent cover of Salsola kali, the most abundant nonmycotrophic annual, decreased by one-half to one-third with inoculation. Mycorrhizal hyphae and spores were...
Since the initial discovery of double fertilization in angiosperms in 1898, a number of reports of double fertilization-like events in the genus Ephedra have appeared. Until recently, convincing documentation of double fertilization in Ephedra had not been presented. In Ephedra nevadensis, following entry of a single binucleate sperm cell into the egg cell, one sperm nucleus migrates in a chalazal direction to fuse with the egg nucleus. Contemporaneous with this first fertilization event, the ventral canal nucleus regularly migrates from its initially apical position within the egg cell to a more central position within the egg cytoplasm, where it fuses with a second sperm nucleus. Based on quantitative microspectrofluorometric...
A new specimen from the Middle Eocene Evacuation Creek Member of the Green River Formation in northeastern Utah shows a twig with several leaves of Populus wilmattae Cockrell and a fruiting raceme attached. This specimen establishes for the first time the type of fruits borne by P. wilmattae and provides additional characters with which to assess its taxonomic and evolutionary status. An associated seed shows attached placental hairs like those of extant species of Populus The Green River fossil differs from extant Populus species in having basically palmate leaf venation and in bearing its fruiting axis on a young twig. In other aspects, the fossil species is remarkably similar to the extant species Populus mexicana....
Allelic variation in seedlings from 60 North American populations of the alien annual grass Bromus tectorum was determined at 25 loci using starch gel electrophoresis. Populations were collected from four regions; east of the Rocky Mountains, Nevada and California, the Intermountain West, and British Columbia. Compared to other diploid seed plants, genetic variation within these populations of B. tectorum is low: 4.60% of loci are polymorphic per population, with an average of 1.05 alleles per locus and a mean expected heterozygosity of 0.012. Although 2,141 individuals were analyzed, no heterozygous individuals were detected, and consequently, mean observed heterozygosity is 0.000. Extensive deviations from Hardy-Weinberg...
The effects of soil texture and grazing by cattle on the production of seeds of Bouteloua gracilis were evaluated for a semiarid grassland in northeastern Colorado. Ten locations were chosen to represent the range in soil textures and grazing intensities found at the Central Plains Experimental Range research site. Number of flowering culms, inflorescences and seeds, length of each flowering culm, total biomass of reproductive structures (culms, inflorescences, and seeds), and basal area were assessed for 96 B. gracilis plants at each location. Community-level estimates of density of flowering culms and density of viable seeds were made for each location. Both soil texture and grazing by cattle were important to...
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Single sequence repeat (SSR) and amplified fragment length polymorphic (AFLP) molecular marker genotypes in cheatgrass (Bromus tectorum) were compared to published data on phenotypic variation in seed dormancy, vernalization requirement, and resistance to the pathogen Ustilago bullata. Several features of cheatgrass facilitated this study: it is a recent invader in the western United States, has considerable phenotypic polymorphism, and is an obligate self-pollinator. Forty self-pollinating lines from four populations common to the three phenotypic data sets were analyzed for molecular genetic variation using seven SSR loci and 31 AFLP loci. We examined correlations between distance matrices using the Mantel test...
Biological invasions can be substantially influenced by the genetic sampling associated with a species? introduction. As a result, we assessed the genetic and evolutionary consequences of the entry and spread of the invasive grass Bromus tectorum (cheatgrass) across the United States midcontinent through an analysis of 54 populations, using enzyme electrophoresis. On average, these populations display 1.04 alleles per locus (A), 4.1% percent polymorphic loci per population (%P) and an expected mean heterozygosity (Hexp) value of 0.009. Heterozygotes, which have been rarely reported for B. tectorum in North America, occur in three populations in the midcontinent and are likely novel multilocus genotypes that arose...
Atriplex confertifolia (Chenopodiaceae) consists of ploidy races extending from diploid through decaploid and is dissected into many racial groups by cytological and flavonoid relationships. On the basis of morphology, the species can be divided into two major subdivisions, one centered in western Nevada and inhabiting chiefly the Great Basin, and one centered in the Colorado Plateau. Western Nevada plants are distinguished by smaller and narrower leaves, as well as by darker spines and other charactristics. Because western Nevada is situated in the lee of the Sierra Nevada Range, it received reduced amounts of rainfall during Pleistocene and Holocene times. These reduced leaf dimensions of A. confertifolia of the...
Gas exchange studies were carried out on Artemisia tridentata during the course of a growing season using microclimatically controlled cuvettes and infrared gas analysis. A definite seasonal pattern of net photosynthesis emerged. This pattern was influenced by the interaction of four major factors: plant water potential, leaf temperature, irradiation, and stage of phenological development. In spring and early summer, when plant water stress was minimal, photosynthesis rate was mainly correlated with leaf temperature and irradiation. During mid and late summer, increased plant water stress and phenological changes assumed at least equal importance with temperature and irradiation in limiting net photosynthesis. Indeed,...
A newly recovered twig with attached leaves and flowers from the Eocene Green River Formation of Utah provides the basis for recognizing a new, extinct genus of Salicaceae sensu lato (s.l.). Pseudosalix handleyi gen. et sp. nov. has alternate lanceolate leaves with pinnate, semicraspedodromous venation and a serrate margin with glandular teeth. The inflorescence is terminal on the twig and is unisexual, composed of flowers organized in a paniculoid cyme, with lateral paraclades of pedicellate flowers. The attached pistillate flowers have four prominent sepals that are valvate in bud, spreading but basally fused at anthesis; the single pistil of each flower is ovoid with three or four longitudinal sutures, indicating...
At Mono Lake, California, we investigated field water relations, leaf and xylem chemistry, and gas exchange for two shrub species that commonly co-occur on marginally saline soils, and have similar life histories and rooting patterns. Both species had highest root length densities close to the surface and have large tap roots that probably reach ground water at 3.4-5.0 m on the study site. The species differed greatly in leaf water relations and leaf chemistry. Sarcobatus vermiculatus had a seasonal minimum predawn xylem pressure potential (?pd) of -2.7 MPa and a midday potential (?md) of -4.1 MPa. These were significantly lower than for Chrysothamnus nauseosus, which had a minimum ?pd of -1.0 MPa and ?md of -2.2...
    map background search result map search result map Seasonal pattern of net photosynthesis of Artemisia tridentata Correlation between molecular markers and adaptively significant genetic variation in Bromus tectorum (Poaceae), an inbreedingannual grass Correlation between molecular markers and adaptively significant genetic variation in Bromus tectorum (Poaceae), an inbreedingannual grass