bluuebunny/crossref_metadata_2025_split huggingface dataset:
STRUCTURAL PATTERN IN ALPINE TUNDRA VEGETATION
Authors: Welden Charles 
Published: January 2018

Several aspects of the spatial pattern of plants were investigated in six very different stands in the alpine tundra of the Colorado Front Range. Pattern was related to the internal structure of the stands, to interactions among the species, and to microhabitats within the stands.Evidence from species‐species associations and species ordinations clearly divided the stands into two groups. The first was characterized by thin, coarse, unstable soils, low plant cover, and nurse‐plant establishment. The second group was characterized by deeper, more mature, and more stable soils, higher plant cover, and more competition between species.Pattern evidence allowed some species to be categorized as competitors, ruderals, or stress‐tolerators in the context of the alpine vegetation. The two groups of stands also differed in the relative importance of species with these “strategies.”
SEX DIFFERENTIAL FLORAL LONGEVITY, NECTAR SECRETION, AND POLLINATOR FORAGING IN A PROTANDROUS SPECIES
Authors: Devlin B. , Stephenson A. G. 
Published: January 2018

Sex differential nectar production, floral longevity and pollinator foraging were examined in Lobelia cardinalis, a self‐compatible, protandrous species that is hummingbird pollinated. The staminate phase of the flowers lasts significantly longer and produces significantly more nectar (total sugar) per day than the pistillate phase of the flowers. Additional pollen is presented throughout the staminate phase.Because inflorescences of L. cardinalis mature acropetally, the nectar reward on any given day is greatest at the top of the inflorescence (where staminate phase flowers are located). Hummingbirds appear to be sensitive to this pattern of nectar presentation as they most commonly began foraging in the middle of an inflorescence and proceeded upward. This foraging pattern tends to promote outcrossing and suggests that staminate phase flowers are visited more often than pistillate phase flowers. We conclude that L. cardinalis emphasizes the male function at anthesis. Others have hypothesized that the features of this species are a logical consequence of intrasexual selection, but further research is needed before we place great confidence in a sexual selection interpretation of our data.
AERODYNAMICS OF WIND POLLINATION IN SIMMONDSIA CHINENSIS (LINK) SCHNEIDER
Authors: Niklas Karl J. , Buchmann Stephen L. 
Published: January 2018

Wind tunnel analyses of Simmondsia chinensis (Link) Schneider or “jojoba” were conducted to quantify the behavior of airborne pollen grains around individual branches and leaves and near individual carpellate flowers. Field data (wind velocity) were used to ensure a correspondence between wind tunnel and natural conditions. Based upon the visualization of individual pollen grain trajectories, it is concluded that pollen deposition on stigmatic surfaces is influenced by large‐scale aerodynamic patterns, generated by foliage leaves, and small‐scale airflow patterns, formed around and by floral parts and stigmas. Leaves are seen to deflect airborne pollen grains into trajectories that can intersect ambient airflow at 90° angles, showering decumbent carpellate flowers with pollen. Similarly, flowers can deflect pollen upward and downwind, toward other flowers. The extent of floral bract and sepal recurvature is shown to influence the extent of pollen deposition by determining the characteristic airflow pattern around stigmas.Available evidence concerning the relatively recent evolutionary transition to anemophily in Simmondsia is interpreted within the context of morphological adaptations and exaptations favoring wind pollination.
GENOMICALLY BASED GENERA IN THE PERENNIAL TRITICEAE OF NORTH AMERICA: IDENTIFICATION AND MEMBERSHIP
Authors: Barkworth Mary E. , Dewey Douglas R. 
Published: January 2018

Dewey and Löve have suggested that generic limits in the Triticeae should be determined by the genomic data, taxa with different genomic constitutions being placed in different genera. According to this interpretation, nine genera of perennial Triticeae occur in North America. Five of these (Critesion, Elymus, Leymus, Pascopyrum, and Pseudoroegneria) include species native to North America; the other four (Agropyron, Elytrigia, Psathyrostachys, and Thinopyrum) are represented only by introduced species. Four hybrid genera of perennial Triticeae also occur in North America, × Elyleymus, × Pseudelymus, × Leytesion, and × Elytesion, the last being a new generic hybrid name necessitated by the treatment presented here. The number of naturally occurring intergeneric hybrids in North America is 18 according to this treatment whereas Bowden, using more traditional generic treatments, recognized 22 such hybrids in North America.For nonhybrid genera, an identification key and a brief description are provided, together with a table showing the taxa included in each genus. For hybrid genera, the species are merely listed. Several new combinations, mostly of hybrid taxa, are presented in order to accommodate the revised generic treatment.
LOSS AND UPTAKE OF15N‐AMMONIUM IN SUBMERGED SOILS OF A CATTAIL MARSH
Authors: Dean John V. , Biesboer David D. 
Published: January 2018

The uptake, distribution, and recovery of nitrogen by field populations of T. latifolia L. (cattails) were determined using (15NH4)2SO4. The results show that 75.3% (53.6% in the plant and 21.7% in the soil) of the isotopically labeled nitrogen added to sampling cylinders containing a single cattail plant could be recovered at the end of one growing season, whereas only 34.6% could be recovered from control cylinders. The increased recovery of 15NH4+‐nitrogen in cylinders containing actively growing T. latifolia compared to cylinders not containing plants suggests that T. latifolia rapidly assimilates labeled nitrogen before it is lost via denitrification or uptake by free‐living soil microorganisms.Measurements of redox potentials in a 60‐cm‐deep field core planted or not planted with T. latifolia showed that only the top 2 and 5 cm of the water column was oxidized (greater than 200 mv at pH 7), respectively. The remaining 58 and 55 cm of the column, including the soil‐water interface, was reduced (less than 200 mv at pH 7). The presence or absence of actively growing T. latifolia plants in the soil cores did not appear to alter significantly the redox profile. The presence of an oxidized zone overlying a reduced zone in cores collected from the field indicates that a portion of the 15NH4+‐nitrogen added to cylinders during the field experiment may have been lost through nitrification‐denitrification reactions.
EVOLUTIONARY TRENDS IN DION (ZAMIACEAE)
Authors: Sabato Sergio , De Luca Paolo 
Published: January 2018

Distribution, ecology, and morphology of the species of Dion are presented. The genus Dion is distributed in Mexico and in Honduras, where it is generally scattered and restricted to rocky, steep habitats.On the basis mainly of the morphology of the seeds, of the seedlings, and of the female cones, three natural groups were recognized. The first group, which is the most distinct morphologically, is made up of D. mejiae endemic to Honduras. The second group is made up of D. spinulosum and D. rzedowskii, whose distribution is restricted to a very small area in Mexico. They appear to be the only Dion spp. to be adapted to moist and shaded habitats. The third group is made up of the remaining spp. of Dion, all Mexican in distribution. They appear to be well adapted to open and dry habitats generally. Stems, female cones, and seeds show the trends to decreasing size from south to north in this group.A key of the genus is given.
VASCULAR CONNECTION BETWEEN LATERAL ROOTS AND STEM IN THE OPHIOGLOSSACEAE
Authors: Chau Robert I. 
Published: January 2018

The vascular connection between lateral roots and stem in the Ophioglossaceae and in two leptosporangiate fern species was examined. Two types of connections were found: “gradual” connections, which resemble leaf traces in ontogeny and morphology, and “abrupt” connections, which resemble the connections between lateral roots and their parent roots.Gradual root‐stem connections occur in the genera Ophioglossum and Helminthostachys and in Woodwardia virginica. They are initiated in shoot apices distal to the level where cauline xylem elements mature. They resemble leaf traces in being provascular (procambial) strands that connect the cauline stele with the future vasculature of lateral appendages. As with leaf traces, gradual connections are part of the provascular and, later, protoxylem continuity between stems and lateral appendages. Gradual connections have many features in common with leaf traces, and the term root trace is applicable to them.The order of radial maturation of the primary xylem in gradual connections varies in different parts of the connections. It is endarch near the intersection with the cauline stele and exarch where the connections intersect root steles. Gradual connections resemble the transition regions of certain seed plants where protoxylem is also continuous from stem to root and the order of maturation is found to change continuously from stem to root.Abrupt connections occur in Botrychium and Osmunda cinnamomea. They develop in shoot apices at levels where cauline xylem is mature or maturing. The mature xylem does not dedifferentiate, so provascular and protoxylem continuity of the kind found in root traces does not occur. Also, reorientation of the order of maturation does not occur in abrupt connections. Xylem connectors are found in the region where radially oriented elements of the connections abut the longitudinally oriented cauline elements. Abrupt connections resemble the connection of secondary roots with their parent root systems since xylem connectors and the lack of continuity are also features found in these vascular systems.The resemblance of the vascular pattern of the fern root trace to the transition region of seed plants suggests that the radicle is more closely comparable to the cladogenous roots of pteridophytes than hitherto supposed.
HEAVY METAL ACCUMULATION AND THE NATURE OF EDAPHIC ENDEMISM IN THE GENUS CALOCHORTUS (LILIACEAE)
Authors: Lee Fiedler Peggy 
Published: January 2018

Bulb and leaf tissues from five species in the genus Calochortus and the soils from collection sites were analyzed for cation and trace element concentrations. All five species, only three of which are considered ultramafic endemics, possessed high concentrations of nickel and copper in both the bulbs and leaves, but not at levels high enough (> 1% dry wt) to be considered hyperaccumulators. Only moderate to trace amounts of cobalt and chromium were detected in both plant tissues. Calcium‐magnesium ratios, typically low in ultramafic soils and plants, were low in bulb tissue, but two to 10 times higher in leaf tissue.The ability to tolerate excessively high levels of nickel and other heavy metals may be a physiological exaptation of the genus Calochortus and not necessarily an evolutionary response by several species to life on an ultramafic substrate. The nature of “serpentine” endemism is discussed in the context of heavy metal accumulation by various plant species.
DEMOGRAPHIC ASPECTS OF COEXISTENCE IN ENGELMANN SPRUCE AND SUBALPINE FIR
Authors: Shea Kathleen L. 
Published: January 2018

The mechanisms for the maintenance of coexistence of Engelmann spruce and subalpine fir in subalpine forests of the Colorado Front Range were examined by comparing age, size, and spatial distributions of spruce and fir in two adjacent, previously logged sites of differing moisture availability. Adult tree ages were calculated from stem cores, while seedling ages were calculated from a multiple regression equation based on diameter, height, and number of branch whorls. Tree size was measured by height and diameter; spatial distributions were described by Morisita's index of dispersion.Cumulative age and size distributions were significantly different in the two species, with greater longevity and a larger overall size in spruce than fir. Both species showed a significant linear relationship between size and age, while fir showed a faster height growth rate than spruce. The linear relationship beween age and size was much closer in seedlings than in adults. Seedling spatial distribution was highly clumped in both species, but mature trees showed little or no clumping. Because both species are mainly wind dispersed, the greater clumping in spruce than in fir seedlings suggests that spruce have more specific establishment requirements than fir. Colonization patterns indicated that spruce seedlings were primarily found in forest gaps or associated with fir canopy trees, while fir seedlings were more commonly found in the forest, associated with either spruce or fir canopy trees. Tree density, growth rates, and mortality rates were higher in the wet site, with spruce showing the largest between site differences. These data suggest a new hypothesis for coexistence stating that Engelmann spruce and subalpine fir are maintained as codominants because the greater longevity and size of spruce is balanced by the faster height growth and more flexible seedling establishment requirements of fir.
RELATIVE POLLINATOR EFFECTIVENESS AND EVOLUTION OF FLORAL TRAITS IN SPATHIPHYLLUM FRIEDRICHSTHALII (ARACEAE)
Authors: Montalvo Arlee M. , Ackerman James D. 
Published: January 2018

We studied the relative effectiveness of different pollinators of Spathiphyllum friedrichsthalii Schott for 15 months on Barro Colorado Island, Panama. Pollen‐foraging stingless bees (Apidae: Trigona) made 87% of floral visits. Experiments showed that these bees pollinate flowers, and correlations of fruit‐ and seed‐set with visitation frequencies and floral contact times suggested that they were responsible for the majority of seeds produced. Fifteen species of fragrance‐foraging, male euglossine bees (Apidae: Euglossini) collectively accounted for a small portion of seed‐set in fewer than 27% of the inflorescences. Neocorynura (Halictidae) were pollen thieves and were unimportant as pollinators.We propose that euglossine and stingless bees differentially influence outcrossing rates and the evolution of floral traits of S. friedrichsthalii. Foraging behavior of male euglossines should allow for more long‐distance pollen flow whereas stingless bees are likely to promote near‐neighbor and geitonogamous pollinations. We discuss why the prolonged male phase of anthesis in this protogynous species may be maintained through pollination by stingless bees rather than male euglossines. Furthermore, although the floral fragrance is attractive to many species of male euglossines, it attracts few individuals. This condition may represent an intermediate step in the evolution of predominant pollination by male euglossines.
EFFECT OF AGING ON FLOWERING OF THE AXILLARY BUDS OF PHARBITIS NIL
Authors: Owens Vivian , Paolillo Dominick J. 
Published: January 2018

In Pharbitis seedlings, aging is associated with definite trends in the pattern of flowering of the axillaries: 1) the locus of maximum flowering is displaced continuously upward, 2) there is a continuous loss of responsiveness to induction from the base of the plant, upward, 3) flowering of the axillaries is suppressed in general when the terminal bud fails to flower, and 4) flowering at the distal nodes regresses when the terminal bud fails to flower. Phenomena 1 and 2 start at the base of the plant and move progressively upward, whereas 3 and 4 are tied to the possibly rhythmic responses of the terminal buds to floral induction, with aging.Buds at axils that form after induction are capable of flowering. Buds at nodes that flower maximally range in development from those not visible with a stereomicroscope to those with enlarging apices ready to form the first leaf primordia at the time of induction. Axillaries that have formed leaf primordia fail to flower in response to one inductive night.
BIOMASS ALLOCATION AND GEOMETRY OF THE CLONAL FOREST HERB LAPORTEA CANADENSIS: ADAPTIVE RESPONSES TO THE ENVIRONMENT OR ALLOMETRIC CONSTRAINTS?
Authors: Menges Eric S. 
Published: January 2018

Using a conceptual model, I predicted the direction of biomass allocation and geometric responses to several environmental variables for Laportea canadensis, a clonal forb dominating the herbaceous stratum of many North American floodplain and mesic forests. Laportea stems and plants, especially dominant ones, generally (60%) respond as predicted to canopy opening, conspecific leaf area and density, and poor drainage, but are merely reduced in growth when growing on sandier soils. However, allometric relationships explain most of the variation in geometry and allocation. Still, variation in geometry and allocation (as great as among 21 species of herbs studied by Givnish [1982]), helps explain the success of Laportea in a range of microenvironments.In upland forests, stems in canopy gaps are tallest but allocate relatively less biomass to leaves than shaded stems, suggesting that interherb competition is the major problem faced under canopy gaps. Leaf morphology also changes with increasing canopy opening—individual leaves are larger, heavier, and thicker and are displayed on more steeply ascending petioles. Floodplain plants respond to light gaps mainly with changes in leaf morphology and display.With increasing conspecific density and leaf production, Laportea stems in both uplands and floodplains grow taller, allocate relatively more biomass to stems, and display leaves higher on the stem. The allocation and geometry of taller stems are more independent of density, and more closely affected by tree‐canopy opening, than are small stems.Intermediate soil textures in floodplains promote maximum Laportea production; variations in other factors are less important. Poorly drained soils in floodplains (heavy‐textured soils at low elevations) cause decreased Laportea height and absolute leaf weight, but increase relative allocation to leaves and roots, as predicted. On the other hand, Laportea appears poorly adapted to sandier soils. Rather than responding to sandier soils as predicted, Laportea's overall growth is reduced.Geometric responses of Laportea to environment are mediated by allometric realities: an increase in height favored in productive environments produces a concomitant decrease in relative leaf allocation. Although predicted (presumably adaptive) shifts are significant when plant size is accounted for, most of the variation in allocation and geometry is due to allometry.
ELECTROPHORESIS IS MODIFYING OUR CONCEPTS OF EVOLUTION IN HOMOSPOROUS PTERIDOPHYTES
Authors: Haufler Christopher H. 
Published: January 2018

Analyses of electrophoretically detectable enzyme variants in homosporous pteridophytes are facilitating the development of new insights into their genetics and evolution. The number of isozymes per enzyme indicates that homosporous pteridophytes are genetic diploids, in spite of the fact that they have high chromosome numbers. High levels of heterozygosity and genetic variability in sporophytic populations indicate that many diploid species are outcrossing with inbreeding representing a derived character state. Because the congeneric homosporous pteridophyte species analyzed to date have low genetic identities, allozymic characters are also proving to be useful as genomic markers for elucidating patterns of reticulate evolution.The accumulated data suggest that the genetic system of homosporous pteridophytes differs fundamentally from that of seed plants. The present genomic constitution of extant taxa may be the result of repeated cycles of allopolyploidy followed by gene silencing and extinction of progenitor taxa. Alternatively, the original homosporous pteridophytes may have had high chromosome numbers. Although current species probably evolved recently, their phylogenetic roots may be difficult to trace because even closely related pteridophytes are genetically distant and extinction has obliterated the ancestral intermediates between lineages. These hypotheses can and should be tested using a combination of molecular, phylogenetic, and population biology methods.
EFFECTS OF FIRE ON CLONAL GROWTH AND DYNAMICS OF PITYOPSIS GRAMINIFOLIA (ASTERACEAE)
Authors: Hartnett David C. 
Published: January 2018

The rhizomatous perennial Pityopsis graminifolia was studied in a Florida sandhill community in an annually burned site, a periodically burned site, and a site that has been protected from fire since 1965. These different fire regimes significantly affected the demography and life histories of both plants and plant parts in this clonal species. Fires resulted in reductions in ramet biomass and height, and an increase in the (root + rhizome)/shoot biomass ratio. Burning also decreased the total number of flower heads and new rhizomes produced per ramet. However, the survivorship of initiated rhizomes was greater in burned sites and resulted in a larger number of established daughter ramets per clone. As a result, in burned sites there was a shift in clone structure toward larger numbers of smaller ramets, but there were no significant reductions in seed or rhizome production on a per genet basis.The results showed that the responses to fire in P. graminifolia are different when measured at the genet vs. ramet level and that the effects of fire on clones can be explained by demographic responses of plant parts. Population regeneration in the study sites was dependent on successful clonal ramet production because no seedling recruitment was observed. This suggests that disturbances other than fire are important for new genet recruitment in these clonal populations.
GROWTH AND DEVELOPMENT OF THE MALE GAMETOPHYTE OF GINKGO BILOBA WITHIN THE OVULE (IN VIVO)
Authors: Friedman William E. 
Published: January 2018

The mature male gametophyte of Ginkgo biloba can be divided into two regions: a large saccate structure that is suspended within the fertilization chamber above the archegonia, and a pervasive, highly branched haustorial system that ramifies through the intercellular air spaces of the apex of the nucellus. This morphology appears to differ in many ways from the simpler more typical male gametophytes of most other groups of seed plants.Growth and development of the male gametophyte of Ginkgo biloba were studied using computer reconstruction techniques to generate images of the gametophyte from data derived from serial sections through the ovule. These investigations reveal that morphological development of the male gametophyte of Ginkgo biloba is divided into three distinct phases: 1) Germination, characterized by an initial brief period of diffuse growth. This phenomenon has not been described for any other seed plant male gametophyte; 2) Initiation of tip growth and the formation of a tubular body, as typifies all seed plant male gametophytes. In Ginkgo, this is accompanied by a high degree of branching, giving rise to an extensively branched haustorial system; 3) Late swelling of the proximal unbranched portion of the gametophyte resulting in formation of the saccate structure that is characteristic of the mature gametophyte. This process appears to be very similar to late development in cycad male gametophytes.Thus, despite the seemingly anomalous morphology of the mature male gametophyte of Ginkgo biloba, specific patterns of growth and development are in many ways similar to growth processes expressed by the male gametophytes of some or all major groups of seed plants.