bluuebunny/crossref_metadata_2025 huggingface dataset:
ADVENTIVE EMBRYOGENESIS IN CITRUS I. THE OCCURRENCE OF ADVENTIVE EMBRYOS WITHOUT POLLINATION OR FERTILIZATION
Authors: Wakana Akira , Uemoto Shunpei
Published: January 2018

Anatomical studies of unfertilized undeveloped seeds from open‐ and control‐pollinated fruits of ten facultative apomictic Citrus cultivars were carried out with the aid of light and epifluorescence microscopes. With or without pollination, adventive embryos autonomously developed at all positions in the nucellus in all cultivars. The adventive embryos initiated at the chalazal end of the nucellus were more vigorous than those initiated at the micropylar end. Because of the lack of endosperm and poor seed development, however, all adventive embryos within the unfertilized seeds terminated their development at the globular or early cotyledonary stages and were unable to germinate under natural conditions. The capability of unfertilized seeds to develop varied from species to species. Growth of the adventive embryos was dependent on nucellus size, but the growth rate of adventive embryos relative to nucellus size was different in different species. Neither pollination, fertilization nor subsequent zygote and endosperm development further stimulated adventive embryo initiation. Conversely, pollination and subsequent fertilization of other seeds in the same fruit slightly, but significantly, suppressed adventive embryo growth in the unfertilized seeds. These facts concerning adventive embryogenesis in unfertilized seeds indicate that neither pollination nor fertilization is essential for in vivo adventive embryogenesis and that normal endosperm is necessary for perfect development of adventive embryos initiated only in the micropylar half of the nucellus.
ASPECTS OF THE MYCORRHIZAL ECOLOGY OF PRAIRIE DROPSEED, SPOROBOLUS HETEROLEPIS (POACEAE)
Authors: Ebbers Bert C. , Anderson Roger C. , Liberta Anthony E.
Published: January 2018

Vesicular‐arbuscular mycorrhizal (VAM) fungal colonization of prairie dropseed and rhizosphere spore abundance were sampled seasonally at two sites in Illinois. At Goose Lake Prairie (GLP), Gaussian ordination of 49 vegetation stands, using plant cover data for 40 species, assigned stands x‐vector values and ordered them along a soil moisture‐nutrient gradient. Prairie dropseed cover data plotted over ordered stands yielded a significant Gaussian curve across a relatively narrow gradient segment. In contrast, colonization and spore abundance had significant negative linear correlations with stand x‐vector values that decreased from the drier, low‐nutrient portion of the gradient to the wetter, high‐nutrient sector. Variation in spore abundance suggested that no VAM fungal species responded to environmental gradient conditions in a manner similar to that of prairie dropseed. The differential responses of host and VAM mycobionts across the gradient suggest that their respective success may be partially independently determined or limited by different parameters. Also, the generally ubiquitous VAM fungal distributions suggest that the host may be more sensitive to gradient conditions than its mycobiont associates.

Colonization and spore abundance at GLP were significantly negatively correlated with available Ca and Mg, and pH. Spore abundance was significantly positively correlated with available K. Neither colonization nor spore abundance were significantly correlated with available P, total N, or organic matter. Seasonally, patterns of VAM colonization and rhizosphere spore abundance varied, having significant positive correlations at GLP and Weston Cemetery Prairie (WCP) in some seasons but not others.

In general, colonization levels were highest in fall 1983 for GLP and fall 1984 for WCP. For 1984, increasing colonization was observed from spring (WCP) or summer (GLP) to fall.
CLONAL ANALYSIS OF CELL LINEAGE PATTERNS IN PLANT DEVELOPMENT
Authors: Poethig R. Scott
Published: January 2018

Somatic sectors induced by ionizing radiation provide a great deal of information about cell lineage patterns in both plants and animals. Somatic sectors arise when the dominant allele of a mutation with a visible, cell‐autonomous phenotype is lost as a result of a deletion or somatic recombination. In addition to marking the fate of cells in a primordium at different stages of development and in different tissues, this technique also provides information about the distribution, orientation, rate, and duration of cell division. The technology and underlying assumptions of this method, termed clonal analysis, are described in this paper.
PALEOBIOLOGY OF DISTINCTIVE BENTHIC MICROFOSSILS FROM THE UPPER PROTEROZOIC LIMESTONE‐DOLOMITE “SERIES,” CENTRAL EAST GREENLAND
Authors: Green J. W. , Knoll A. H. , Golubic S. , Swett K.
Published: January 2018

Populations of Polybessurus bipartitus Fairchild ex Green et al., a large and morphologically distinctive microfossil, occur in silicified carbonates of the Upper Proterozoic (700–800 Ma) Limestone‐Dolomite “Series,” central East Greenland. Large populations of well‐preserved individuals permit reconstruction of P. bipartitus as a coccoidal unicell that “jetted” upward from the sediment surface by the highly unidirectional secretion of extracellular mucopolysaccharide envelopes. Reproduction by baeocyte formation is inferred on the basis of clustered envelope stalks produced by small cells. Sedimentological evidence indicates that P. bipartitus formed surficial crusts locally within a shallow peritidal carbonate platform. Among living microorganisms a close morphological, reproductive, and behavioral counterpart to Polybessurus is provided by populations of an as yet undescribed cyanobacterium found in coastal Bahamian environments similar to those in which the Proterozoic fossils occur. In general morphology and “jetting” behavior, this population resembles species of the genus Cyanostyton Geitler (1925), but reproduces via baeocyte formation. Polybessurus is but one of the more than two dozen taxa in the richly fossiliferous biota of the Limestone‐Dolomite “Series.” This distinctive population, along with co‐occurring filamentous cyanobacteria and other microfossils, contributes to an increasingly refined picture of ecological heterogeneity in late Proterozoic oceans.
REPRODUCTIVE BIOLOGY OF ASTER CURTUS (ASTERACEAE), A PACIFIC NORTHWEST ENDEMIC
Authors: Clampitt Christopher A.
Published: January 2018

Aspects of the reproductive biology of Aster curtus were investigated to shed light on the current rarity of the species, which is endemic to grasslands of western Washington and Oregon. A bagging experiment showed that excluding insect pollinators significantly decreased the production of viable seeds. Where insects were allowed access, seed production by this perennial forb was not unusually low. Seeds of A. curtus exposed to light germinated over a wide range of temperatures, but few seeds germinated in the dark. Stratification improved germination. Aster curtus was shown to be a stress‐tolerant species that grows very slowly under all conditions. Although seed production and germination do not appear to limit A. curtus, competition from other species probably restricts seedling recruitment in undisturbed communities. Habitat loss due to agriculture, urban expansion, and the natural conversion of grasslands to Douglas fir forests appears to be a more important reason for the historic loss of A. curtus populations.
INFLUENCE OF MICROGRAVITY ON CELLULAR DIFFERENTIATION IN ROOT CAPS OF ZEA MAYS
Authors: Moore Randy , Fondren W. Mark , McClelen C. Edward , Wang Chia‐Lien
Published: January 2018

We launched imbibed seeds of Zea mays into outer space aboard the space shuttle Columbia to determine the influence of microgravity on cellular differentiation in root caps. The influence of microgravity varied with different stages of cellular differentiation. Overall, microgravity tended to 1) increase the relative volumes of hyaloplasm and lipid bodies, 2) decrease the relative volumes of plastids, mitochondria, dictyosomes, and the vacuome, and 3) exert no influence on the relative volume of nuclei in cells comprising the root cap. The reduced allocation of dictyosomal volume in peripheral cells of flight‐grown seedlings correlated positively with their secretion of significantly less mucilage than peripheral cells of Earth‐grown seedlings. These results indicate that 1) microgravity alters the patterns of cellular differentiation and structures of all cell types comprising the root cap, and 2) the influence of microgravity on cellular differentiation in root caps of Zea mays is organelle specific.
ORIGINS OF SOLANUM LASIOCARPUM AND S. REPANDUM
Authors: Heiser Charles B.
Published: January 2018

Solanum candidum of tropical America is very similar to S. lasiocarpum of southeastern Asia and S. sessiliflorum, a wild and domesticated plant of the Amazon basin, is very similar to S. repandum, a weed and domesticated plant of Oceania. Artificial hybrids between S. candidum and S. lasiocarpum are fertile, and it is postulated that S. lasiocarpum resulted from a Spanish introduction of S. candidum to Asia. Hybrids between S. repandum and S. sessiliflorum show considerable reduction in fertility and abnormalities at meiosis, whereas hybrids of both S. candidum and S. lasiocarpum with S. repandum are fertile. It is concluded that it is likely that S. repandum did not arise from S. sessiliflorum but from S. lasiocarpum or S. candidum. This would mean that the similarity of S. repandum to S. sessiliflorum results from convergence.
MYCORRHIZAL AND CLIPPING EFFECTS ON ANDROPOGON GERARDII PHOTOSYNTHESIS
Authors: Wallace L. L. , Svejcar T.
Published: January 2018

Mature Andropogon gerardii (Vitman) plants were placed in a 2 × 2 factorial treatment regime with clipping soil fumigation as main treatment effects. Plants were grown in a greenhouse using a Latin square design; pots were watered daily, and fertilized weekly with a low phosphorus nutrient solution. Photosynthesis and conductance were measured prior to and after a clipping which removed about 23% of the total leaf length of clipped plants. Fumigation reduced mycorrhizal colonization levels from 34.3 to 7.4%. Conductance was not affected by either treatment. Fumigated, clipped plants had significantly lower photosynthetic rates than their nonfumigated counterparts. However, there were no significant differences between fumigated and nonfumigated unclipped plants. The initial slope of the photosynthetic light response curve was significantly greater for the nonfumigated plants. Greater mycorrhizal development in nonfumigated plants appeared to be beneficial only when the host plants were under defoliation stress.
OVULE INVERSION IN THE EARLIEST CONIFERS
Authors: Mapes Gene
Published: January 2018

Recent investigations of ovulate conifer cones from southern Europe and midcontinent North America have independently documented that certain Paleozoic walchians have inverted ovules, rather than the erect ovules previously thought to characterize the most primitive conifers. Reinvestigation and consideration of other walchian conifers, including Moyliostrobus and Lebachia piniformis (sensu Florin), reveals that they also had inverted ovules. These different patterns of ovule orientation demonstrate that the nature and the polarity of the character states are dramatically different than popularly believed, and the shift from megasporophyll to ovuliferous cone‐scale occurred within the Paleozoic walchians.
COMPARATIVE ANATOMY OF SOME PARENTS AND HYBRIDS OF THE HAWAIIAN MADIINAE (ASTERACEAE)
Authors: Kim InSun
Published: January 2018

Comparative leaf morphology and anatomy was examined in five species and four hybrids involving three genera of Hawaiian Madiinae (Asteraceae). The comparisons included Argyroxiphium grayanum, Dubautia ciliolata subsp. ciliolata, D. knudsenii subsp. knudsenii, D. scabra subsp. leiophylla, D. scabra subsp. scabra, and Wilkesia gymnoxiphium, and the hybrids A. grayanum × D. scabra subsp. leiophylla, D. ciliolata subsp. ciliolata × D. scabra subsp. scabra, D. knudsenii subsp. knudsenii × D. scabra subsp. leiophylla, and W. gymnoxiphium × D. scabra subsp. leiophylla. Foliar morphology, leaf tissue organization, and various characters of stomata and trichomes were compared, using epidermal peels, cross and paradermal sections, and clearings of leaves. Pronounced anatomical differences among these closely related taxa were characterized, and effects of hybridization on the expression of anatomical features were documented. Most comparisons of parents and hybrids revealed statistically significant differences in leaf size, distribution of adaxial and abaxial stomata, and marginal and surface trichomes. In most instances hybrids demonstrated intermediate status in their foliar characters, indicating that these features are inherited from both parents. However, differences in foliar characters were usually of sufficient magnitude to allow recognition of hybrids as well as parents.
CERATOPTERIS RICHARDII: APPLICATIONS FOR EXPERIMENTAL PLANT BIOLOGY
Authors: Hickok Leslie G. , Warne Thomas R. , Slocum Mary K.
Published: January 2018

The homosporous fern life cycle provides numerous advantages for experimental studies. In particular,Ceratopteris richardii, because of its rapid life cycle and ease of culture, is a useful model system for a variety of basic and applied studies of plant development, genetics and molecular biology. Use of the gametophytic generation in screens for specific types of mutations has resulted in the successful isolation and characterization of mutations conferring tolerance or insensitivity to a variety of herbicides, NaCl, plant growth regulators and other agents. Recent progress in the development of a system for introducing exogenous DNA inCeratopteriscells provides a foundation for future studies of the molecular basis of selected traits.
STRUCTURAL SPECIALIZATION OF THE SITE OF RESPONSE TO VECTORIAL PHOTO‐EXCITATION IN THE SOLAR‐TRACKING LEAF OF LAVATERA CRETICA
Authors: Werker Ella , Koller Dov
Published: January 2018

Structural features of the pulvinus of the solar‐tracking leaf of Lavatera cretica L. that are involved in its capacity for omnidirectional and fully reversible bending in response to vectorial excitation of the lamina were studied by light‐ and scanning electron microscopy. Pulvini that had bent in the plane at right angles to the midvein were bisected along that plane and the symmetrical tissues of the expanded and contracted flanks were compared. The pulvinus contains a central vascular core and exhibits a transversely furrowed exterior. These specialized features enable the fully mature tissue of this region of the petiole to bend reversibly. The epidermis, chlorenchyma, peripheral collenchyma, and cortical parenchyma in the pulvinus form concentric, radially symmetric sheaths around the vascular core and exhibit structural features in their cell walls that would allow considerable changes in cell volume and consequently enable the omnidirectional bending of this pulvinus. Thickened wall portions of the pulvinar epidermis and peripheral collenchyma exhibit a highly specialized architecture, consisting of alternating thick and thin strips, that enhances their flexibility, while maintaining mechanical support. Cell walls of the chlorenchyma and the cortical parenchyma are thin and capable of reversible infolding. Those of the cortical parenchyma also exhibit numerous prominent transverse pit fields, indicative of anisotropic orientation of their microfibrillar lattice transverse to the pulvinar axis. This orientation is compatible with elastic deformation of the cortical parenchyma cells along the pulvinar axis. Filament‐like cytoplasmic strands were observed along the walls of pulvinar motor cells, predominantly transverse to the pulvinar axis, but their function (if any) in volume changes of these cells is unknown.
HOW CEREAL GRASS SHOOTS PERCEIVE AND RESPOND TO GRAVITY
Authors: Kaufman Peter B. , Brock Thomas G. , Song Il , Rho Young Bok , Ghosheh Najati S.
Published: January 2018

The leaf‐sheath pulvinus of grasses presents a unique system for studying gravitropism, primarily because of its differences from other organs. The mature pulvinus is a discrete organ specialized for gravitropism: it is nongrowing in the absence of gravistimulation and capable of displaying a graviresponse independent of the rest of the plant. In this paper we present a model for gravitropism in pulvini based on recent findings from studies on the mechanisms of graviperception and graviresponse. According to this model, amyloplasts play an essential role in perceiving a change in the orientation of the pulvinus. The perception of this reorientation leads to the enhanced synthesis and release from conjugate of the auxin IAA, and the increased conjugation of gibberellin, on a localized basis. Because there is a graded growth promotion across the gravistimulated pulvinus, it is suggested that the observed hormonal asymmetry is actually an indication of a linear gradient of hormone concentration, as well as hormone response, across the pulvinus. It is further suggested that the linear gradient of hormone concentration may be predominantly the result of local changes in hormone level, rather than a product of hormonal movement into or across the pulvinus.
CHANGES IN SOIL AGGREGATION ASSOCIATED WITH TALLGRASS PRAIRIE RESTORATION
Authors: Jastrow J. D.
Published: January 2018

To investigate the dynamics of soil aggregation associated with the restoration of cultivated soil to tallgrass prairie, changes in soil aggregation and aboveground production were compared in a corn field, restored prairie plantings of various ages (second, fifth, eighth, and eleventh growing season), and an uncultivated prairie remnant. The restored prairie was also compared with a long‐term (fourteenth growing season) ungrazed pasture dominated by Eurasian grasses. All plots were located on similar soils. The regression model, Y = 95.8 ‐ 56.2/X (R2 = 0.93), best described the relatively rapid recovery of water‐stable soil aggregates >0.2 mm diameter with time (in years) since cultivation. Similar models were also found to describe changes in the percentages of aggregates > 1 and > 2 mm diameter. Aggregates > 0.2 and > 2 mm diameter were more closely associated with prairie graminoids than with other vegetation categories. However, time without disturbance may be a more important factor in soil aggregate formation than vegetation type, but it was difficult to separate the effects of these two factors in this study. The percentage of aggregates > 0.2 mm diameter was found to be significantly higher (P = 0.0553) in the oldest restored prairie than in ungrazed pasture although the former had been cultivated more recently. This suggests that C4 prairie graminoids may confer some advantage over introduced C3 Eurasian grasses for the development of water‐stable aggregates in soils of the Prairie Peninsula.
SPATIAL AND TEMPORAL VARIATION IN CHASMOGAMY AND CLEISTOGAMY IN OXALIS MONTANA (OXALIDACEAE)
Authors: Jasieniuk Marie , Lechowicz Martin J.
Published: January 2018

Chasmogamous (CH) and cleistogamous (CL) flower production was investigated in natural populations of the perennial herb Oxalis montana in southern Quebec, Canada. Every 10–12 days during two flowering seasons, we recorded the reproductive output of approximately 2,000 plants distributed among five forest sites. The percentage of plants flowering, proportion of flowering plants producing CH and CL flowers, CH and CL flower number per flowering plant, and the proportion of flowers that are CL differed significantly among sites and corresponded to site differences in forest type and habitat quality. Unlike patterns in most CL species, however, reproduction by cleistogamy increased in sites with habitat conditions favorable to plant growth and sexual reproduction, and decreased in less productive sites. Chasmogamous and CL flower production increased with increasing plant size but plant size explained a significantly greater proportion of the variation in CL flower numbers. The percentage of flowering plants producing CH flowers decreased between years while the proportion of CL flowers increased at all sites during the second flowering season. The somewhat unusual aspects of reproduction in Oxalis may stem from its perennial habit which allows use of stored resources in adjusting the balance of cleistogamy versus chasmogamy in different environmental regimes.
DREWRIA POTOMACENSIS GEN. ET SP. NOV., AN EARLY CRETACEOUS MEMBER OF GNETALES FROM THE POTOMAC GROUP OF VIRGINIA
Authors: Crane Peter R. , Upchurch Garland R.
Published: January 2018

Drewria potomacensis gen. et sp. nov. from the Lower Cretaceous Potomac Group of Virginia (Zone I, probably Aptian) provides the first definite Mesozoic megafossil record of Gnetales. The stems are slender, display no evidence of secondary growth, and show axillary monopodial branching. Attached leaves are opposite and decussate, borne at swollen nodes, and have clasping sheathing bases. Each leaf is oblong, up to 20 mm long, and has a dense network of longitudinally aligned subepidermal fibers. Leaf venation consists of two, or possibly three pairs of longitudinal parallel veins that form a reticulum at the apex and higher‐order crossveins that form apically oriented chevrons. Reproductive structures consist of short, loose spikes that are borne in dichasially arranged groups of three. The dichasia are either terminal or lateral in the axil of a leaf. Reproductive units of the lateral spikes in a dichasium contain seeds, each surrounded by at least one pair of opposite, broadly elliptical or ovate bracts. Characters of D. potomacensis that suggest a gnetalean relationship include the opposite bracts surrounding the seeds, the network of subepidermal foliar fibers, and the distinctive leaf venation, which is very similar to that seen in the cotyledons of extant Welwitschia. Other features consistent with a gnetalean relationship include opposite and decussate leaves, swollen nodes, and the dichasial arrangement of the reproductive spikes. Masses of polyplicate gnetalean pollen comparable to that of extant Welwitschia occur in the same bed as the megafossils. The morphology of D. potomacensis indicates that it was an herb or possibly a shrub. The growth habit of D. potomacensis and associated plants, combined with the sedimentary occurrence of the fossils, indicate that this species and perhaps related taxa were important components of early successional vegetation during the mid‐Cretaceous.
PHYLOGENETIC COMPARISON OF LARGE NUCLEAR DNA CONTENTS OF DIFFERENTIATED CELLS IN THE ROOTS OF EQUISETUM, TRADESCANTIA, AND HORDEUM
Authors: Murry Lynn E. , Christianson M. L.
Published: January 2018

Nuclear DNA of meristematic, epidermal and root cap cells from the roots of three vascular plants—the cryptogam, Equisetum hyemale L, and the phanerogams, Tradescantia Clone 02 and Hordeum vulgare L.—was measured with quantitative Feulgen microspectrophotometry. Epidermal cells of all three species and root cap cells in both phanerogams contained up to 8fold the amount of nuclear DNA found in their respective meristematic telophase nuclei. In general, the large amounts of nuclear DNA parallel development and differentiation in the epidermis regardless of phylogeny, habitat, or degree of domestication. However, comparisons of the increase in nuclear DNA contents in the various epidermal cell types among these three species suggest that the mechanisms giving rise to these increases may differ phylogenetically and may represent another character in which cryptogams and phanerogams diverged in their evolution.
CHARACTERIZATION OF THE NUCLEAR DNA OF HORDEUM VULGARE ROOT HAIRS: AMPLIFICATION DISAPPEARS UNDER SALT STRESS
Authors: Murry L. E. , Christianson M. L. , Alfinito S. H. , Garger S. J.
Published: January 2018

InHordeum vulgareL., the nucleus of differentiating root hairs contains amplified, extrachromosomal DNA sequences. Cytophotometry shows that the nuclei of trichoblasts and root hairs grown under normal conditions contain up to 50% more DNA than those grown in 200 mM salt. Although the root hairs develop and differentiate under salt stress, amplification of their nuclear DNA is suppressed. From this, we conclude that amplification is not necessary for differentiation at the cellular level. Characterization of the amplified nuclear DNA of the root hair is based on the physical/chemical nature of the DNA. The amplified sequences separate as a satellite band when total nucleic acids are centrifuged on CsCl gradients. Enzyme restriction of the satellite and main bands with Msp I and Hpa II followed by agarose gel electrophoresis shows that the satellite band is not more highly methylated than the main band. Restriction of the root hair DNA with EcoRI reveals repetitive DNA sequences not seen in similarly restricted whole root, leaf or salt‐stressed root hair preparations. While these unique, repetitive sequences in the 2–6 kb region of the gel do not hybridize with ribosomal, chloroplast, or mitochondrial DNAs, RNA hybridization shows that some of them are transcribed. We believe that the amplified sequences are extrachromosomal based on their selective degradation during root hair senescence, their separation as a satellite band and their restriction patterns.
COMPARATIVE PATTERNS OF NET PHOTOSYNTHESIS IN AN ASSEMBLAGE OF MOSSES WITH CONTRASTING MICRODISTRIBUTIONS
Authors: Alpert Peter , Oechel Walter C.
Published: January 2018

Effects of plant water content, previous desiccation, photon flux density, and temperature on rate of net photosynthesis were measured in the common species in the assemblage of desiccationtolerant mosses that dominates the flora on granitic boulders at a semiarid site in the inland chaparral of San Diego County, California. Species differed significantly in their responses to water content, desiccation, and light. Species previously found to occur in microsites of lower water availability attained maximum net photosynthesis at lower water contents and showed greater ability to recover from prolonged desiccation. Species found in microsites of lower light availability had higher rates of net photosynthesis at low photon flux density. Results suggest that differences in potential rates of net photosynthesis partly determine relative ability of these species to colonize xeric or dark microsites, but that other factors also determine microdistribution.
MORPHOGENESIS AND EXPERIMENTAL ASPECTS OF GROWTH AND DEVELOPMENT OF THE MALE GAMETOPHYTE OF GINKGO BILOBA IN VITRO
Authors: Friedman William E.
Published: January 2018

Morphogenesis in the morphologically complex male gametophyte of the seed plant Ginkgo biloba was investigated in vitro. These studies reveal that although development in vitro is far more variable than in vivo, it is still characterized by the sequential expression of three distinct patterns of growth: initial diffuse growth of the tube cell, initiation and establishment of tip growth (which may be accompanied by branching), and radial swelling of the gametophyte. Time lapse photography shows that branching of the male gametophyte results from two distinct types of initiation events: one apical (“primary branching”), and the other subapical (“secondary branching”). Experimental manipulation of the growth medium indicates that exogenous sucrose levels strongly influence the likelihood of expression of normal morphogenetic processes. High levels of sucrose tend to inhibit both the initiation of tip growth following initial diffuse growth, as well as branching of the gametophyte. Low sucrose levels appear to promote a normal pattern of early establishment of tip growth and subsequent branching of the gametophyte, similar to development of the gametophyte in vivo.
DEVELOPMENT OF TRISTYLY IN PONTEDERIA CORDATA (PONTEDERIACEAE). I. MATURE FLORAL STRUCTURE AND PATTERNS OF RELATIVE GROWTH OF REPRODUCTIVE ORGANS
Authors: Richards Jennifer H. , Barrett Spencer C. H.
Published: January 2018

Pontederia cordata is a tristylous, self‐incompatible emergent aquatic. Measurements of reproductive organs in mature flowers and developing buds and analysis of relative growth rates of the styles, filaments, and floral tube were used to analyze the developmental processes that result in reciprocal positioning of reproductive parts among the style morphs. Flowers are trimerous with two series of three tepals, two series of three stamens, and a tricarpellate ovary with a single ovule. Each flower has stamens of two lengths, but the two lengths correspond to upper vs. lower position in the zygomorphic flowers, not to the two series initiated in the primordium. Morph‐dependent variation in stigma height depends on differences in style length, not ovary length. Differences among morphs in anther height result from differences in the position of filament insertion on the floral tube and differences in filament length. Styles of the three morphs develop to different lengths as a result of two distinct processes. Styles of L and M morphs develop at different rates with the L style growing more rapidly than the M style, whereas styles of the S morph have a brief period of rapid growth followed by early inhibition. Stamen growth in the S morph also differs qualitatively from that in the L and M morphs, which are distinguished from each other by quantitative differences in growth rates. Results indicate that the developmental processes that result in the complementary arrangements of organs in different morphs are morph‐specific. An attempt is made to integrate the findings of this study with the model for genetic control of tristyly.
GENETIC ANALYSIS OF ANTHERIDIOGEN SENSITIVITY IN CERATOPTERIS RICHARDII
Authors: Scott Rodney J. , Hickok Leslie G.
Published: January 2018

The pheromone antheridiogen promoted the production of males in gametophyte populations of the fern Ceratopteris richardii. Two homozygous strains of this species exhibited markedly different sensitivities to the pheromone, resulting in populations with either high or low frequencies of males. The two strains were characterized by dose responses to antheridiogen and by gametophyte population density studies to investigate the effect of antheridiogen produced within cultures. Analyses of Fl hybrids and an F2 generation indicated that differences in the antheridiogen responses of the two parental strains are associated with either one or two nuclear genes.
REGULATION OF THE TIMING OF POLLEN GERMINATION BY THE PISTIL IN TALINUM MENGESII (PORTULACACEAE)
Authors: Murdy William H. , Carter M. Eloise Brown
Published: January 2018

In angiosperms selection among male gametophytes may take place between the time a flower is pollinated and the time its ovules are fertilized. With insect pollination, a surplus of male gametophytes in the form of pollen grains may be deposited on the stigma of a pistil and this provides the potential for gametophytic competition and selection. In all plants examined from two Talinum mengesii populations, pollen germination was delayed for up to two hours after pollination. In plants of two other populations pollen germination was not delayed or the time of germination varied. Reciprocal pollinations between plants with and without the delay trait and pollinations at different times during anthesis revealed that the timing of pollen germination was regulated by the maternal parent. Theoretically, the effect of the delay trait would be to promote the accumulation of pollen on the stigma and induce simultaneous germination. This would intensify intermale competition and provide a mechanism for the maternal parent to influence the paternal parentage of its offspring.
A TEST OF SEVERAL HYPOTHESES FOR THE DETERMINATION OF SEED NUMBER IN AMELANCHIER ARBOREA, USING SIMULATED PROBABILITY DISTRIBUTIONS TO EVALUATE DATA
Authors: Gorchov David L. , Estabrook George F.
Published: January 2018

The number of seeds per fruit is variable within Amelanchier arborea trees. Because A. arborea flowers are five‐carpellate and each carpel contains two ovules, we were able to use the pattern of seed maturation within fruits to test whether the failure of some ovules to develop into seeds is determined by mechanisms operating at the level of carpels, such as stigma‐clogging, or by mechanisms operating at the level of ovules, such as ovule infertility. The presence of one‐, two‐, and zero‐seeded carpels demonstrated that the number of ovules developing into seeds was not due entirely to carpel‐level phenomena. In order to test the hypothesis of carpel independent seed development, without the assumption that all ovules have the same probability of developing into seeds, it was necessary to use simulation, since no conventional statistical models were appropriate. Analysis of this simulation allowed us to reject carpel independent processes as the only determinant of seed number. A mixed model of seed development, in which some carpels fail entirely and ovules in the remaining carpels develop equiprobably, was shown to be consistent with the data.
EFFECT OF ENVIRONMENTAL PRETREATMENT ON TOLERANCE TO COPPER AND ZINC IN THE MOSS FUNARIA HYGROMETRICA
Authors: Shaw Jonathan
Published: January 2018

The effect of pretreatment on zinc‐ and copper‐enriched media on subsequent tolerance of F. hygrometrica to these metals was tested in three individuals each from a tolerant and a nontolerant population. Some individuals showed a significant response to pretreatment and some did not, and those that did varied in both intensity and direction. In general, pretreatment affected protonemal growth more than stem production. Although pretreatment effects were demonstrated, genetic differences between individuals and populations were more important determinants of the level of tolerance.
GENETIC AND MATERNAL EFFECTS ON SEEDLING CHARACTERS OF SOLIDAGO ALTISSIMA (COMPOSITAE)
Authors: Weis Arthur E. , Hollenbach Heidi G. , Abrahamson Warren G.
Published: January 2018

The relative contributions of genetic and maternal factors to phenotypic variation were studied in seedlings of the clonal herb Solidago altissima L. Pairwise crosses were made to establish 19 full‐sibships. Because crosses were reciprocal, each parent served as seed parent to half its offspring and as pollen parent to the other half. For 18 characters, genetic variation was estimated from the between sibship variance and maternal variation from the variance between maternal groups within sibships. Early in the growing season, maternal effects exerted strong influence over variation in leaf and stem dimensions, while genetic influences were weak or absent. At the end of the season genetic influences on leaf and stem dimensions, relative biomass allocation between stem and leaves, and the propensity to flower were significant but maternal effects were not. However, both genetic and maternal influences were found on the number and lengths of new rhizomes.

Phenotypic, genetic, and maternal correlation matrices were examined through principal component analysis for trade‐offs among vegetative growth, clonal expansion and floral reproduction which could constrain the evolution of life history patterns. At the phenotypic level, seedlings with strong vegetative growth produced more and longer rhizomes, and were more likely to flower. Genetically, correlations among these functions were weak or absent. Strong maternal contributions to seedling vegetative growth correlated positively with the number and length of rhizomes. Thus, no trade‐offs acting during the seedling stage were found. However, there were indications of a genetically influenced trade‐off between the number of rhizomes produced in the seedling year with the size of the ramets produced in the second year.
DIFFERENCES IN LEAF STRUCTURE, CHLOROPHYLL, AND NUTRIENTS FOR THE UNDERSTORY TREE ASIMINA TRILOBA
Authors: Young Donald R. , Yavitt Joseph B.
Published: January 2018

To investigate differences in leaf structure, chlorophyll and nutrients on terminal branches of the understory tree Asimina triloba, the first (proximal) and the last (distal) leaves to develop in the spring were compared. Proximal leaf expansion was completed before the overstory canopy was fully closed but distal leaf expansion occurred during and after the development of the overstory canopy. Fully expanded proximal leaves were 76% smaller in area, were 18% thicker and had 36% more stomates per m of leaf area when compared to distal leaves. In addition, maximum stomatal conductance to water vapor was greater (150 vs. 120 mmol m−‐2s−‐1) and the minimum PPFD required for maximum conductance was higher (200 vs. 150 μmol m−‐2s−‐1) for the proximal leaves. Chlorophyll content was also greater for proximal leaves, but nitrogen and phosphorus contents were lower throughout the entire summer. Seasonal measurements indicated an increase in chlorophyll a content and reductions in nitrogen content throughout the summer growth period for leaves from both positions. The results suggest that distal and proximal leaves differed physiologically and that the measured differences were related to the changing irradiance environment during leaf development. The time of leaf expansion, as indicated by leaf position on the branch, may be an important consideration when examining the water and photosynthetic relations of understory trees.
A NUMERICAL ANALYSIS OF FLAVONOID VARIATION IN ARNICA SUBGENUS AUSTROMONTANA (ASTERACEAE)
Authors: Wolf Steven J. , Whitkus Richard
Published: January 2018

Species of Arnica subgenus Austromontana produce a total of 23 leaf flavonoids, including simple and methylated flavone and flavonol glycosides as well as highly methylated flavone aglycones and a 6‐hydroxylated flavone. Most of the taxa exhibit considerable interpopulational variability, with the number of compounds per population ranging from 2 to 14. Analysis of flavonoid variation in 113 populations representing all 9 species of the subgenus was carried out using cluster analysis, principal components analysis, and binary discriminant analysis. Results indicate the flavonoid profile of the very rare A. viscosa is the most distinctive in the subgenus. Although exhibiting considerable interpopulational variability, all populations of A. gracilis, a hybrid taxon, form a very distinct and cohesive group, supporting its recognition at the specific level. Additionally, chemical diversification from A. cordifolia has taken place largely in the Klamath region of Oregon and California. The range of variability exhibited by A. cordifolia is reflected in these Klamath region derivatives.
CO‐REQUIREMENT FOR CALCIUM AND POTASSIUM IN THE GERMINATION OF SPORES OF THE FERN ONOCLEA SENSIBILIS
Authors: Miller John H. , Wagner Patricia M.
Published: January 2018

Spores of Onoclea sensibilis L. do not germinate on distilled H2O if they are pretreated for sufficient time with dilute NaClO solution. However, spores will germinate, after NaClO pretreatment, on a simple mineral medium containing the major and trace elements. Complete germination after pretreatment also is obtained on a solution containing only Ca2+ and K+ as the cations, but neither ion by itself is sufficient. Rb+, but not Li+ or Na+, can replace K+. Hypochlorite‐treated spores do not require the continuous presence of Ca2+ and K+ to germinate; exposure during the first 4 hr of culture, with the remainder of the time on distilled H2O, is sufficient. Extraction of spores with ethylene glycol bis(aminoethyl ether) tetraacetic acid [EGTA] makes their germination dependent on Ca2+, as reported by other workers, but it does not produce a co‐requirement for K+. Colorimetric analysis with arsenazo III confirms that Ca2+ is extracted from Onoclea spores by NaClO. Extractable Ca2+ amounts to about 78 nmol/mg spore dry wt. Of this amount, 31% is contained in the perispore. The perispore comprises 13% of the total spore dry wt.
MECHANICAL PROPERTIES WITHIN THE GROWTH ZONE OF CORN ROOTS INVESTIGATED BY BENDING EXPERIMENTS I. PRELIMINARY OBSERVATIONS
Authors: Silk Wendy Kuhn , Beusmans Jack M. H.
Published: January 2018

Bending experiments were performed to analyze mechanical properties within the apical 15 mm of the primary root of corn, Zea mays. Force required to maintain a root in a bent shape declined with the logarithm of time, indicating significant stress relaxation. Spatial distributions of local curvature, strain due to bending, and geometrical moment of inertia were calculated from digitized photographs of mechanically bent roots during and after imposition of a bending moment. When roots were bent to nonuniform curvature (maximum K = 3 cm–1 at the location 8 mm from the root tip), “irreversible” curvature (residual curvature 4 hr after release of the bending moment) was approximately 44% of initial curvature. This percentage of irreversible curvature (and associated bending strain) was uniform throughout the growth zone. When roots were bent to uniform curvature of either 1 cm–1 or 1.67 cm–1, “springback” curvature (residual curvature after two minutes of bending) varied from 60% of initial curvature in the apical regions (at 4 mm) to 85% of initial curvature at the base of the growth zone. The results are consistent with a model in which total strain is proportional to stress, and irreversible strain at a particular location is proportional to total strain at the same location.
PATTERNS OF PRE‐ AND POSTFERTILIZATION RESOURCE ALLOCATION WITHIN AN INFLORESCENCE: EVIDENCE FOR INTEROVARY COMPETITION
Authors: Solomon Bruce Peary
Published: January 2018

I investigated the distribution of ovules and seeds on the inflorescence of Solanum Carolinense L. (Solanaceae). Ovules did not appear to vary in size, but the number of ovules per ovary and the size of ovaries decreased significantly along the inflorescence (from basal to distal positions). Experimental removal of basal ovaries at an early stage resulted in increased ovary size and number of ovules in distal ovaries, suggesting a dynamic system of control. Mature fruits displayed a similar pattern of decreasing mass and seed number with position along the infructescence. It is not clear whether the patterns of allocation to fruits are related to the patterns of allocation to ovaries in a simple cause‐and‐effect relationship. However, a satisfying hypothesis that explains these and other patterns of allocation is that they are all manifestations of, or adaptations to, interovary competition along the inflorescence.
ISOZYME NUMBER IN SUBTRIBE ONCIDIINAE (ORCHIDACEAE): AN EVALUATION OF POLYPLOIDY
Authors: Chase Mark W. , Olmstead Richard G.
Published: January 2018

The Oncidiinae has attracted attention because of the variation it exhibits in chromosome number, n = 5–30, which is greater than the range in the rest of the Orchidaceae. The genus Psygmorchis, with n = 5 and 7, has been a particular focus of controversy, and many authors have suggested that 5 and 7 are the base numbers for the subtribe. The other taxa in the subtribe presumably evolved through hybridization and polyploidy. Other workers have found that the lowest counts correlate with derived morphological conditions and have hypothesized that these low numbers result from aneuploid reductions, while higher numbers are associated with ancestral morphologies and are not the result of polyploidy. These two hypotheses were evaluated by determining isozyme numbers for 13 enzymes in species that span the chromosomal range known for the Oncidiinae (n = 5–30). Isozyme number has been shown to be a reliable indicator of polyploidy in angiosperms because polyploids display isozyme multiplicity relative to diploids. This analysis revealed no differences among species in isozyme number for the enzymes examined. Therefore, our data reject the hypothesis that species with higher chromosome numbers are polyploid.
JANE COLDEN (1724–1766) AND HER BOTANIC MANUSCRIPT
Authors: Smith Beatrice Scheer
Published: January 2018

Jane Colden's original manuscript, containing descriptions and drawings made about 1753 to 1758 of over 300 New York State plants, is housed in The British Museum (Natural History), London. Colden's detailed and careful descriptions in the new Linnaean system were evidently taken from living specimens growing on the 3,000‐acre Colden estate near Newburgh, New York. Letters reveal that her contributions to botany were recognized by the prominent botanists of her day, including John Bartram, Collinson, Garden, Ellis, and Linnaeus, but over a century and a half passed before a more intimate acquaintance with her manuscript established Jane Colden as America's first woman botanist.
PERMINERALIZED FRUITS AND SEEDS FROM THE PRINCETON CHERT (MIDDLE EOCENE) OF BRITISH COLUMBIA: ARACEAE
Authors: Cevallos‐Ferriz Sergio , Stockey Ruth A.
Published: January 2018

Some of the most conspicuous fruit and seed remains from the Middle Eocene Princeton chert locality (Allenby Formation) are assignable to the Araceae. Several thousand campylotropous, reniform, spiny seeds 2.5–3.2 mm long x 1.8–2.3 mm wide have been found dispersed in the chert. Two fruits, each with a single locule and at least eight ovules, show three distinct wall layers and appear to have been fleshy. The two layers of seed integument have pitted isodiametric sclereids aligned in radial rows, the outermost being thinner walled. Spines are borne in three rows on the dorsal seed surface while the ventral side is flattened. Idioblasts that probably contained raphides are present in the outer integument. Nucellar tissue is attached to the integument for most of its length and is well‐preserved in some seeds near the chalaza and in the large conical shaped area beneath the micropyle. Endosperm cells with dark contents and curved, linear, monocotyledonous embryos are present in some seeds. Sections of seeds of living araceous taxa of the subfamilies Monsteroideae (Epipremnum, Rhodospatha) and Lasioideae (Urospatha, Cyrtosperma) were made for comparison. The fossil seeds represent a new taxon most closely related to Cyrtosperma, Keratosperma allenbyensis Cevallos‐Ferriz et Stockey gen. et sp. nov., Family: Araceae, Subfamily: Lasioideae, Tribe: Lasieae. The Princeton remains are the oldest described seeds of this tribe known to date and add to our knowledge of the subtropical elements of the Princeton flora.
GENETIC STRUCTURE OF POPULATIONS OF GEOGRAPHICALLY RESTRICTED AND WIDESPREAD SPECIES OF ASTRAGALUS (FABACEAE)
Authors: Karron Jeffrey D. , Linhart Yan B. , Chaulk Christine A. , Robertson Cliff A.
Published: January 2018

Evolutionary theory predicts that species with small ranges and few individuals will exhibit low levels of genetic polymorphism. We investigated the population genetic structure of two locally endemic and two geographically widespread species of Astragalus. To facilitate direct comparisons among these congeners, three populations of each species were sampled in a consistent manner and scored for allozyme polymorphisms at 12 loci. Genetic polymorphism was lower in restricted A. linifolius and A. osterhouti than in widespread A. pectinatus. However, the restricted species do exhibit a moderate level of isozyme variation, comparable to that of widespread A. pattersoni and higher than has been detected in several other rare plant taxa. As measured by Wright's F statistics, there were no consistent differences between the restricted and widespread taxa with respect to the organization of genetic variation. FST values were low in all taxa, indicating little heterogeneity among populations.