bluuebunny/crossref_metadata_2025 huggingface dataset:
A QUANTITATIVE STUDY OF TISSUE DYNAMICS DURING CLOSURE IN THE TRAPS OF VENUS'S FLYTRAP DIONAEA MUSCIPULA ELLIS
Authors: Fagerberg Wayne R. , Allain Dawn
Published: January 2018

The mechanisms by which Venus's Flytrap (Dionaea muscipula Ellis) close are not clearly understood, and several conflicting models have been proposed. We have measured the dynamics of five trap tissues from three trap regions during full closure of young, fully developed, previously unclosed traps. Closure was divided into three distinct stages: 1) Capture–occurred immediately after stimulation of the trigger hairs and involved the rapid inward flexure of the trap margin and tynes. This motion interlocked the tynes, effectively capturing the prey. This was the only rapid movement of the trap; 2) Appression–completed by 30 min poststimulation, was characterized by contact of the margins; and 3) Sealing–completed by 1 hr poststimulation, was characterized by a sealed “digestive” sac formed around the potential prey, also by tight appression and recurved bending of the trap–margins. Major tissue dynamics that facilitated changes in trap morphology (hence, closure) occurred in different regions of the trap during different periods of time. The first regions where activity occurred were the A and C regions (Fig. 1), after approximately 15 min poststimulation; tissues in the C regions were most active followed by those in the B region of the trap (30 min to 1 hr poststimulation). Thus, shape changes during each stage of closure were the result of temporally separated changes in trap tissue volume. The complete sequence of events was elicited by a single 5–sec period of trigger hair stimulation. Our study showed that changes in the curvature of the trap during closure involved the expansion of opposing tissue groups (i.e., on opposite sides of trap medullary tissues). The pressure from contact of opposing trap lobes during the Appression stage may play an important role in regulating further trap closure and morphology.
PATTERNS OF GENETIC VARIATION IN SALIX SECTION LONGIFOLIAE (SALICACEAE)
Authors: Brunsfeld Steven J. , Soltis Douglas E. , Soltis Pamela S.
Published: January 2018

Enzyme electrophoresis was used to examine genetic relationships within a taxonomically complex group of diploid willows (Salix section Longifoliae). Forty‐eight populations representing seven morphogeographic taxa were analyzed for 15 putative enzyme loci. Levels of genetic variation (A, P, He, and HT) differed greatly among populations, but were generally lower than those reported for other species with similar life history traits. In populations and species from southern latitudes, where populations tend to be smaller and more isolated, genetic variation decreased and population differentiation increased. Genetic identity values suggest that the section is divisible into four major elements: 1) Salix interior, 2) S. taxifolia, 3) the S. exigua group, and 4) S. melanopsis. The first three occupy eastern, southern, and western portions of the continent, respectively. Salix melanopsis is sympatric with the S. exigua group in western North America, but is ecologically distinct. The S. exigua group is differentiated into four major geographic entities: S. hindsiana from west of the Sierras in California and southwest Oregon, S. sessilifolia from west of the Cascades in central Oregon to British Columbia, and a northern and southern race of S. exigua in the Intermountain West. The relationships suggested by allozyme data do not agree with traditional taxonomic concepts. Evidence of hybridization was obtained at five points where taxa come into contact, and Salix fluviatilis may be of hybrid origin. Taxonomic confusion appears to be largely the result of frequent hybridization events and overemphasis of a few highly variable morphological traits. The section appears to be a syngameon undergoing geographic speciation, with one taxon gaining reproductive isolation by a shift in habitat preference.
ROOT PROFILES AND COMPETITION BETWEEN THE INVASIVE, EXOTIC PERENNIAL, CARPOBROTUS EDULIS, AND TWO NATIVE SHRUB SPECIES IN CALIFORNIA COASTAL SCRUB
Authors: D'Antonio Carla M. , Mahall Bruce E.
Published: January 2018

The mat‐forming succulent, Carpobrotus edulis (Aizoaceae), surrounds and grows over many native plant species in California coastal communities. Two shrub species, Haplopappus ericoides and H. venetus var. sedoides, were found to have shallow root systems that occupied the same soil depths as those of C. edulis. In the presence of C. edulis, the normal rooting profiles of the shrubs were displaced downward, although partial overlap with C. edulis remained. Removal of C. edulis from around individuals of both shrub species resulted in higher predawn xylem pressure potentials in shrubs from the removal treatments as compared to controls, suggesting that the surrounding C. edulis was utilizing water that would otherwise have been available to these shrubs. In H. ericoides, predawn xylem pressure potentials of removal treatment shrubs remained higher than those of the controls throughout the remainder of the dry season even though these shrubs showed a marked increase in canopy area after removal of surrounding C. edulis. Removal of C. edulis from around H. venetus also initially led to higher predawn xylem pressure potentials in the removal shrubs as compared to the controls and increased production of new leaves. After this initial period the predawn xylem pressure potentials of the removal shrubs were not significantly different from those of controls, suggesting that the demand for water by the increased leaf areas eventually matched the enhanced water availability resulting from C. edulis removal. Also, the morphology of H. venetus shrubs changed to that more typical of unaffected individuals. Thus, C. edulis significantly affected not only the water relations of these two shrub species but also their shoot sizes and overall morphologies.
THRIPS‐MEDIATED SELF‐POLLINATION OF TWO FACULTATIVELY XENOGAMOUS WETLAND SPECIES
Authors: Baker James Dillon , Cruden Robert William
Published: January 2018

Thrips and/or aphids played an important role in the self‐pollination of two facultatively xenogamous herbs that inhabit wetlands in northwestern Iowa. In both Ranunculus sceleratus and Potentilla rivalis the fruit set and/or successful pollination of plants that were sprayed with malathion to kill thrips and aphids and caged to exclude typical flower visitors was substantially and significantly lower than that of open‐pollinated and caged plants. We observed pollenbearing thrips and aphids on the flowers. The high fruit sets of emasculated flowers of R. sceleratus showed that insects moved pollen between flowers, and our observations of bees collecting pollen and moving between plants suggest that cross‐pollination can occur in both species.
THE EARLIEST REMAINS OF GRASSES IN THE FOSSIL RECORD
Authors: Crepet William L. , Feldman Gwen D.
Published: January 2018

New fossils provide the earliest unequivocal evidence of grasses. Spikelets and inflorescence fragments with included pollen from the Paleocene/Eocene Wilcox Formation in western Tennessee have a suite of diagnostic characters that limits their affinities to Poaceae. Associated vegetative remains are also suggestive of grasses, but are not well enough preserved for an unequivocal identification. These fossils indicate a minimal time of origin for the family, are consistent with an Upper Cretaceous origin of Poaceae, and suggest that as in wind‐pollinated Hamamelididae, wind pollination evolved in grasses or persisted in the grass lineage (if a wind‐pollinated grass sister group is presumed) in dry tropical environments.
SYSTEMATIC IMPLICATIONS OF CHLOROPLAST DNA VARIATION IN THE SUBTRIBE MICROSERIDINAE (ASTERACEAE: LACTUCEAE)
Authors: Jansen Robert K. , Wallace Robert S. , Kim Ki‐Joong , Chambers Kenton L.
Published: January 2018

Phylogenetic relationships among six of the seven currently recognized genera of the subtribe Microseridinae were examined using comparative restriction site mapping of the chloroplast genome. Complete cleavage maps of 17 enzymes were constructed for 35 of the 46 species in the subtribe and six representative outgroup species from four other subtribes of the Lactuceae. A total of 373 restriction site mutations was detected, 180 of which were phylogenetically informative. The chloroplast DNA mutations were used to generate phylogenetic trees using Dollo, Wagner, and weighted parsimony, and the resulting monophyletic groups were evaluated by the bootstrap method. The results indicate that the Microseridinae is paraphyletic because Stephanomeria is nested within the six core genera of the subtribe. Five of the genera of the Microseridinae are monophyletic, whereas Microseris is paraphyletic because one of its species, M. lindleyi, is more closely related to Agoseris and Nothocalais. The distant relationship of M. lindleyi to the rest of the species of Microseris is enigmatic, especially in view of its known involvement in the origin of two allotetraploid species, M. decipiens and M. heterocarpa. The taxonomic implications of these results lead to a revised classification of Microseris in which the genus Uropappus is revived to accommodate M. lindleyi, and a new genus, Stebbinsoseris, is described to include the allotetraploids. The cpDNA phylogeny is used to evaluate the patterns of character evolution within the Microseridinae, as well as to test previous hypotheses that differences in generation time result in unequal rates of chloroplast DNA evolution.
HELICAL FLORAL ORGANOGENESIS IN GLEDITSIA, A PRIMITIVE CAESALPINIOID LEGUME
Authors: Tucker Shirley C.
Published: January 2018

In order to determine the extent of floral ontogenetic differences among species of a genus, six species of Gleditsia were studied. Gledilsia is one of only two leguminous genera known in which there is completely helical succession of floral organs. Floral ontogeny was compared in three species (Gleditsia amorphoides, G. aquatica, and G. triacanthos), and late stages in six species (including the first three plus G. caspica, G. delavayi, and G. japonica). Other unusual primitive developmental features include the unequal‐sized flower primordia which produce flowers of variable merosity. Order of floral development is also loosely controlled, so that flowers of different growth stages are intermixed in the inflorescence. Variable features include the occurrence of floral bracts, merosity of flowers, number of organs, and position of the first organ (sepal) initiated. The inflorescence type, while usually a raceme, often has lateral branches near the base, or fascicles of flowers at some points. A terminal flower often is present, although not in all species. Sex of flowers and inflorescences also varies, although floral initiation tends to include both stamens and carpel primordia. Suppression of one or the other may occur at different stages of development. Carpel orientation also varies; the cleft may be tilted or inverted occasionally. It is proposed that absence of subtending floral bracts influences development so as to favor radial symmetry and establishment of other “chaotic” characters seen in Gledilsia flowers.
DEVELOPMENT OF STRIATE EXINE IN IPOMOPSIS RUBURA (POLEMONIACEAE)
Authors: Takahashi Masamichi , Skvarla John J.
Published: January 2018

Exine formation in Ipomopsis rubura (L.) Wherry (Polemoniaceae) was traced with transmission and scanning electron microscopy. At the early tetrad stage, plasma membranes of microspores invaginate and form a punctate pattern within the callose wall. Protectum is then deposited, taking a punctate pattern corresponding to the plasma membrane. After dissolution of the callose wall, the punctate pattern develops into a striate sculpture by partial thickening of tectum. The mature tectum is thus composed of two layers, the inner punctate and outer striate layers. With the plasma membrane determining the initial tectum pattern within the tetrad, additional sculptural elements are later formed above this pattern during the free microspore stage.
GENDER VARIATION IN BARTSIA ALPINA (SCROPHULARIACEAE), A SUBARCTIC PERENNIAL HERMAPHRODITE
Authors: Molau Ulf
Published: January 2018

Maternal and paternal effects on seed size and reproductive success (RS) were studied in a subarctic population of Bartsia alpina L. (Scrophulariaceae), a hemiparasitic perennial herb forming dense clones in open habitats. The impact of environmental factors was assessed in fertilization and defoliation experiments, and gender specialization of individual genets was investigated in a series of diallel experiments (reciprocal crossings) in the field. Maternal effects on seed weight were much larger than paternal effects, and seed weight was also strongly influenced by resource availability (especially nitrogen). The highest seed weights were usually found when genets were associated with Astragalus frigidus, which seems to be the optimal host species in the population, but similar results were achieved with NPK (nitrogen‐phosphorus‐potassium) fertilization. Defoliation experiments revealed an innate minimum seed weight, below which seed number was affected by resource deprivation. The reciprocal crossing program indicated a high level of gender specialization in individual genets (clones), ranging continuously from almost pure males to almost pure females. Early‐flowering genets showed the highest average male RS, whereas female RS increased in late‐flowering genets. Phenological separation of the genets into ‘early’ and ‘late’ revealed an inverse correlation between male and female performance. Numerous characters contributing to phenotypic gender were measured in the genets, but these characters and functional gender calculations from the diallel experiment were only weakly correlated. It is concluded that simultaneous measures of both male and female RS are needed for a reliable assessment of gender variation.
WHOLE‐PLANT RESPONSES OF BRASSICA CAMPESTRIS (CRUCIFERAE) TO ALTERED SINK‐SOURCE RELATIONS
Authors: Evans Ann S.
Published: January 2018

Plants may respond to developmentally or environmentally induced changes in the relationship between source (assimilate exporting) and sink (assimilate importing) organs through a number of regulatory mechanisms. The purpose of this work was to describe responses in leaf physiology, organ biomass partitioning, and reproduction of Brassica campestris L. to altered sink‐source relations. Partial defoliation early in ontogeny increased sink‐source ratio after 1 day and was accompanied by a significant increase in area‐based photosynthetic capacity. Assimilate was preferentially partitioned to new leaf tissue at the expense of stem and reproductive tissue so that sink‐source ratio and photosynthesis returned to control levels within a week. Bud excision at flower initiation decreased sink‐source ratio; plants in this treatment responded through altered biomass partitioning, but there were no detected changes in leaf physiology. Plants that were hand‐pollinated had decreased specific leaf weight, and within a week, sink‐source ratio increased. Plants that were pollinated and then completely defoliated produced 40% as many seeds as plants that were not defoliated, presumably through stem and/ or fruit photosynthesis, and at the expense of flower production. Together these results illustrate that regulation of sink‐source relations can occur through complex responses at several levels of organization over a wide range of time scales.
ARCHAEOCALAMITES LAZARII, SP. NOV.: THE RANGE OF ARCHAEOCALAMITACEAE EXTENDED FROM THE LOWERMOST PENNSYLVANIAN TO THE MID‐LOWER PERMIAN
Authors: Mamay Sergius H. , Bateman Richard M.
Published: January 2018

Archaeocalamites lazarii, sp. nov., is based on a few vegetative compressions from the mid‐Lower Permian Leonard Series near Fulda, north‐central Texas. It is a minor component of a rich biota that includes sphenophylls, pteridophylls, conifers, conchostracan crustaceans, eurypterids, arachnids, insects, xenocanth sharks, and coprolites attributed to tetrapods. Biota and sedimentology indicate deposition in a small freshwater body on a deltaic floodplain. Leaves of A. lazarii differ in size and posture from those of the widespread and characteristically Mississippian aggregate species A. radiatus; nonpreservation of rooting and reproductive organs prevents interpretation of its phylogenetic relationship with other equisetaleans. The main significance of A. lazarii is that it extends the recorded stratigraphic range of the Archaeocalamitaceae from the lowermost Pennsylvanian (Namurian B) to the mid‐Lower Permian (Artinskian), leaving a hiatus in records of approximately 55 Ma. This Lazarus taxon also occurs with possibly the youngest recorded eurypterid.
DEVELOPMENT OF THE POLLEN TUBE OF ZAMIA FURFURACEA (ZAMIACEAE) AND ITS EVOLUTIONARY IMPLICATIONS
Authors: Choi JungSun , Friedman William E.
Published: January 2018

Compared with pollen tubes of conifers, gnetophytes, and angiosperms, the pollen tube of cycads is exclusively a vegetative structure, uninvolved with the siphonogamous conduction of sperm to an egg. The cycad pollen tube appears to function primarily to obtain nutrients for the extensive growth and development of the male gametophyte. Previous workers have suggested that, similar to an haustorial fungus, the cycad pollen tube penetrates the reproductive tissues of the sporophyte by enzymatically destroying nucellar cells. These earlier studies did not document the precise structural relationship between the growing male gametophyte and its “host” tissue, the nucellus. Pollen tube growth, and its relation to the nucellus, was examined in Zamia furfuracea with light and transmission electron microscopy. Following germination, the pollen tube of Zamia furfuracea grows intercellularly through the subepidermal layers of the micropylar apex of the nucellus. Electron micrographs clearly show additional localized outgrowths of the pollen tube penetrating the walls of individual nucellar cells. Intracellular haustorial growth ultimately leads to the complete destruction of each penetrated cell, and appears to induce the degeneration of proximal unpenetrated nucellar cells. This pattern of intracellular penetration of the sporophyte by the male gametophyte in Zamia furfuracea is fundamentally different from what has been described in any other major group of seed plants (where intercellular growth of the male gametophyte is the rule), and suggests that the heterotrophic and tissue‐specific relationships that male gametophytes of seed plants have with their host sporophytes are substantially more diverse than had previously been known.
BENDING STIFFNESS OF CYLINDRICAL PLANT ORGANS WITH A ‘CORE‐RIND’ CONSTRUCTION: EVIDENCE FROM JUNCUS EFFUSUS LEAVES
Authors: Niklas Karl J.
Published: January 2018

The mechanical behavior of leaves of Juncus effusus L. in bending was investigated in terms of a closed‐form analytical solution derived to predict the bending stiffness of a cylindrical sandwich beam consisting of an outer ‘rind’ (sclerenchyma and chlorenchyma) and an inner ‘core’ (aerenchyma). The elastic moduli (ETOTAL) of intact leaves was measured by means of multiple resonance frequency spectra and compared to that of leaves for which the aerenchymatous core was surgically destroyed. Based on ten leaves, ETOTAL = 22.33 × 104 ± 5.37 ± 104 kg · cm–2 while the elastic modulus of the ‘rind’ was 22.29 × 104 ± 5.69 × 104 kg · cm–2. The elastic modulus of the ‘core’ was estimated at 3.12 × 104 ± 1.42 × 104 kg · cm–2. Load‐deflection curves for three leaf segments indicated leaves were linearly elastic within the range of loading and could be predicted with considerable accuracy based on the closed‐form solution. The aerenchymatous core was found to contribute very little to the bending stiffness of leaves, although its contribution appeared to increase as leaf diameter decreased. Leaves mechanically failed by Brazier buckling when excessively loaded and were best considered to mechanically operate as hollow tubes. Nonetheless, the analytical solution for bending stiffness could be applied and, in theory, can be used to predict the behavior of other plant organs with a ‘corerind’ construction.
GYNOECIAL ONTOGENY AND MORPHOLOGY, AND POLLEN TUBE PATHWAY IN BLACK MAPLE, ACER SACCHARUM SSP. NIGRUM (ACERACEAE)
Authors: Peck Carol Jacobs , Lersten Nels R.
Published: January 2018

The black maple (Acer saccharum Marsh, ssp. nigrum [Michx. f.] Desm.) gynoecium displays classical involute carpel development; carpels form, in mid‐ to late‐summer, as two separate, opposite, hood‐shaped primordia bearing naked megasporangia on inrolled carpel margins. Megasporogenesis, integument initiation, and carpel closure occur in spring; carpels fuse, forming a biloculate ovary with a short, hollow style and two divergent, dry, unicellular papillose stigmas. Transmitting tissues consist of developmentally and morphologically similar trichomes that form along the apparent carpel margins. The path from stigma to micropyle is open, but pollen tubes do not grow entirely ectotrophically. Germinating at the tip of a stigma papilla, a tube grows, apparently under the cuticle, to the papilla base. It then grows between stigma cells to the style, emerging to grow ectotrophically through the style to the compitum, where it passes into one of the locules. Within a locule, the tube grows over placenta and obturator to the micropyle, then between megasporangium cells to the female gametophyte, spreading over the surface near the egg. This study adds to our sparse understanding of gynoecium development and transmitting tissue in relation to pollen tube growth in naturally pollinated woody plants.
ULTRASTRUCTURE OF THE EPIDERMIS OF DEVELOPING COTTON (GOSSYPIUM) SEEDS: SUBERIN, PITS, PLASMODESMATA, AND THEIR IMPLICATION FOR ASSIMILATE TRANSPORT INTO COTTON FIBERS
Authors: Ryser Ulrich
Published: January 2018

The basal part of cotton fibers (Gossypium arboreum and G. hirsutum) was studied with light and electron microscopy in order to improve the understanding of assimilate transport into the fibers during the deposition of the cellulosic secondary wall. Although the distal parts of white cotton fibers are not suberized, a variable amount of suberin was found at the fiber base. This suberin is typically deposited in concentric layers, alternating with polysaccharides. Numerous pits occur in the base of cotton fibers and in ordinary epidermal cells in the periclinal and anticlinal walls. About 25% of the length of periclinal walls is occupied by pits, but only 2% of the anticlinal walls, being pitted mainly in their proximal part. In suberized walls the deposition of suberin is not reduced in the pit region. The pits, whether or not suberized, contain plasmodesmata (22 ± 2.3 and 27 ± 3.3 · μm−‐2 in the periclinal and anticlinal walls of the white lint cultivar of G. hirsutum). Transport of assimilates into the fibers through the symplast is therefore possible. This transport may occur directly from mesophyll cells to fibers, or indirectly via ordinary epidermal cells. The minimum amount of assimilates transported into individual fibers during the phase of secondary wall deposition could be estimated (1.3 pg · fiber−‐1 · sec−‐1), as well as the corresponding symplastic flux of assimilates through the periclinal cell wall, neglecting a possible transport through the anticlinal walls (10−‐3 pg · μm−‐2 · sec−‐1). It is postulated that in the green lint genotype of G. hirsutum and in wild cotton species (not studied in this paper), the uptake of assimilates into the fibers occurs through the symplast, the apoplastic pathway being excluded by the suberization of the fibers during secondary wall formation. Although cultivated, white‐linted cotton species may use the same pathway, loading of assimilates from the apoplast is theoretically also possible, and the relative contribution of both pathways has to be determined experimentally.
LEAF DEMOGRAPHY OF A NEOTROPICAL RAIN FOREST CYCAD, ZAMIA SKINNERI (ZAMIACEAE)
Authors: Clark David B. , Clark Deborah A. , Grayum Michael H.
Published: January 2018

Tropical rain forest understories are extremely light‐limited environments. Little is known about the demography of leaves in these habitats. To determine leaf longevity and causes of mortality for a species in the understory of a neotropical rain forest, we studied 634 leaves on 173 individuals of the cycad shrub Zamia skinneri for 10 yr at the La Selva Biological Station, Costa Rica. Five different seasonal cohorts of leaves were followed. No significant differences among cohorts were found in median leaf longevity, but the cohorts did differ in the proportion of leaves dying in annual intervals from <1 to ≥6 yr. Median minimum time alive for all leaves was 4.6 yr. Epiphyll coverage increased from 0% in the first year of life to 75%‐100% by year 4. Leaf mortality was well described by two separate exponential functions, approximately 10% mortality/yr until year 4, then abruptly increasing to ca. 51%/yr. Of 625 leaf deaths, 77.0% were due to unexplained causes, 16.5% to physical damage by falling litter, 4.8% to attacks by larvae of the lycaenid butterfly Eumaeus minyas, and 1.8% to other causes. Leaf longevity was positively correlated with leaf size. Individuals of Z. skinneri frequently survive more than a century in very dark understory conditions. We suggest that leaf longevity in these circumstances is determined by the inevitable deterioration in leaf carbon balance due to leaf aging and increasing epiphyll coverage, and by loss due to physical damage and attacks by the specialist herbivore.
LEVER ACTION ANTHERS AND THE FORCIBLE SHEDDING OF POLLEN IN TORENIA (SCROPHULARIACEAE)
Authors: Armstrong Joseph E.
Published: January 2018

The anthers of Torenia fournieri were found to shed pollen forcibly by lever action. Anther structure was modified for this function by a flangelike outgrowth of the lateral pollen sac wall forming a lever. When pressed, this lever causes an infolding of the thinner, subadjacent, pollen sac wall forcing pollen from the stomium. A force of 1–1.5 g pressing against the four levers of an anther pair resulted in the forcible shedding of 2,000–3,000 pollen grains in two parallel rows. During the 2‐day anthesis the flowers shift from functioning as males to hermaphroditic outcrossers, and yet only have a pollen:ovule ratio of 98.6, a ratio more indicative of facultative autogamy. The outermost pair of anthers functions on the first day of anthesis, while the second, inner pair functions on both days. In each flower, the 2‐day anther pair produces approximately twice as many pollen grains as the 1 ‐day anther pair, a pollen production highly correlated with the length of their functional lives. This difference in pollen production is apparent in the larger size of the 2‐day anthers, a size difference that first appears with the initiation of the anther primordia.
EFFECTS OF FERTILIZATION ON EPICUTICULAR WAX MORPHOLOGY OF NEEDLE LEAVES OF DOUGLAS FIR, PSEUDOTSUGA MENZIESII (PINACEAE)
Authors: Chiu Shau‐Ting , Anton Lori H. , Ewers Frank W. , Hammerschmidt Raymond , Pregitzer Kurt S.
Published: January 2018

Fertilized stands of Pseudotsuga menziesii were found to have glaucous needles. We investigated the morphological and quantitative characteristics of the epicuticular waxes of needles of fertilized and control trees. Glaucousness was caused by ornate tubular epicuticular wax. Dipping needles in chloroform, which dissolves waxes, eliminated the glaucous appearance. Based on cryostage scanning electron microscopic observations, the epicuticular waxes in the nonstomatal region were much more ornate on the needles of the fertilized trees (experimental needles) than in unfertilized trees (control needles). The stomatal region in both experimental and control needles showed similarly ornate waxes. Quantities of waxes were similar in experimental and control needles. The glaucousness was not the result of greater quantities of wax; rather, fertilization altered wax morphology in the nonstomatal regions.
NEIGHBOR RELATEDNESS AND COMPETITIVE PERFORMANCE IN IMPATIENS CAPENSIS (BALSAMINACEAE): A TEST OF THE RESOURCE PARTITIONING HYPOTHESIS
Authors: Argyres Anneta Z. , Schmitt Johanna
Published: January 2018

The Elbow Room hypothesis for the maintenance of sex depends upon the assumption that intraspecific resource partitioning occurs and increases in magnitude with decreasing genetic similarity of competitors. This assumption leads to the prediction that plants should have greater fitness in competition with nonrelatives than in competition with siblings. Moreover, if a population displays fine scale genetic structure and genetic similarity declines with distance, then resource partitioning should increase with increasing geographical distance between the source locations of the competing genotypes. We tested these predictions in a greenhouse experiment by subjecting inbred Impatiens capensis seedlings to four types of competitors: 1) inbred full sibs; 2) inbred nonrelatives from the same source location; 3) inbred nonrelatives from a source location 30 m away; and 4) inbred nonrelatives from another population approximately 1 km distant. Plant dry weight at harvest increased significantly with seed weight and earlier emergence date, decreased significantly with seed weight and earlier emergence date of the competitor, and varied significantly among maternal seed families. However, there was no significant effect of competitor relatedness or distance between parental locations. The experiment therefore failed to support the resource partitioning hypothesis.
ANATOMICAL AND METABOLIC RESPONSES TO WATERLOGGING AND SALINITY IN SPARTINA ALTERNIFLORA AND S. PATENS (POACEAE)
Authors: Naidoo G. , McKee K. L. , Mendelssohn I. A.
Published: January 2018

The effects of waterlogging and salinity (25 or 325 mol m 3 NaCl) stressors on the anatomy and metabolism of the marsh grasses 5. alterniflora Loisel. and S. patens Aiton (Muhl.) were investigated in a V factorial greenhouse experiment over 30 d. Waterlogging and salinity in combination resulted in anatomical and metabolic responses in both species. Waterlogging reduced soil redox potential and decreased root‐specific gravity significantly in both species. The inadequacy of aerenchyma development under hypoxia to support aerobic root respiration in S. patens was indicated by significant increases in root alcohol dehydrogenase (ADH) activity of 1,752% and 420%, respectively, in the low and high salinity treatments. ADH activity was not increased significantly by flooding of S. alterniflora. Proline concentrations in roots and leaves were low at low salinities and increased significantly at high salinities in both species, but only under drained conditions. Decrease in leaf elongation by high salinity occurred in drained, but not flooded treatments in both species. Under flooded conditions, leaf elongation was significantly greater in S. alterniflora than S. patens. Greatest leaf elongation occurred in flooded low salinity S. alterniflora plants that had the least proline. Although both species are adapted to waterlogging and salinity, S. alterniflora appears to be more tolerant of reducing soil conditions and less responsive to higher salinity than S. patens.
COMPARATIVE FLOWER AND FRUIT MORPHOGENESIS IN COLUBRINA (RHAMNACEAE) WITH SPECIAL REFERENCE TO C. ASIATICA
Authors: Medan Diego , Hilger Hartmut Hugo
Published: January 2018

Flower and fruit morphogenesis of Colubrina asiatica, including aspects of fruit dehiscence and seed morphology, were studied by scanning electron microscopy and serial sectioning. Material from 13 additional species representing most intrageneric diversity was also examined. Organ initiation is simultaneous within each floral whorl and proceeds centripetally. Each petal/stamen pair apparently arises by tangential splitting of an individual primordium. The ontogeny of the three‐locular, semi‐inferior gynoecium follows a pattern common to many Rhamnaceae. At anthesis each uniovulated carpel has an almost independent pollen‐tube pathway, with a subbasal compitum allowing for interconnection between carpels. Protandry, herkogamy, and a tendency to polygamy seemed to occur in C. asiatica. Fruit growth results mainly from postfloral promotion of the previously negligible superior part of the ovary. The explosively to tardily dehiscent capsules include three thin‐walled, dehiscent stones (endocarpids) of inner dermal origin. At maturity, xerochastic (i.e., caused by desiccation), oblique bending of the endocarpids generates a complex dehiscence pattern involving thorough breaking of epicarp and mesocarp. The Colubrina type of fruit may be considered basic within the Rhamnaceae, which is consistent with the putative primitiveness of the genus. A limited potential for specialization is, however, expressed in such traits as explosive dehiscence, persistent arils on the seeds, and dispersal by sea currents (thalassochory).
ON THE HISTORY AND CHARACTERISTICS OF SOME MULTIPLE DISCOVERIES IN BOTANY, 1648–1965
Authors: Troyer James R.
Published: January 2018

Historians and others have given attention to multiple independent discoveries because of their implications for the nature of scientific discovery in general. However, previously published lists of such discoveries include almost no examples from botany. That this has been a matter of oversight is shown by the presentation of 22 cases of multiple botanical discoveries, the circumstances of which are briefly described. These examples show a number of the same general characteristics as those in other fields of science. They range in importance from the broadly sweeping to the narrowly specific, and show various degrees of simultaneity. They illustrate the problems of interpretation involved in judging functional equivalence, identity of central message, and priority. The bearing of some of the examples on various theories of the cause of multiple discoveries is also discussed. It is concluded that multiple discoveries have probably occurred as frequently in botany as in other sciences, and they display the same characteristics and generate the same problems of interpretation.
MYCORRHIZAE IN HAWAIIAN PTERIDOPHYTES: OCCURRENCE AND EVOLUTIONARY SIGNIFICANCE
Authors: Gemma J. N. , Koske R. E. , Flynn T.
Published: January 2018

Forty‐five percent of the Hawaiian pteridophyte flora were examined for mycorrhizae. Vesicular‐arbuscular mycorrhizae were present in 66 of the 89 species examined. Nonmycotrophy was significantly higher in Hawaiian pteridophytes than in non‐Hawaiian pteridophytes. The highest mycorrhizal colonization occurred in the leptosporangiate families Dicksoniaceae, Dryopteridaceae, and Lindsaeaceae. Mycotrophy was lower in the eusporangiate families. Substrate strongly influenced the presence of mycotrophy. Mycorrhizae were present in 83% of terricolous species, in 86% of epilithic species, in 55% of epiphytic species, and absent from aquatic species. A phylogram of pteridophyte families is constructed incorporating the intensity of mycorrhizal colonization as one criterion for classification.
THE SEXUAL AND ASEXUAL LIFE CYCLE OF GLENODINIOPSIS STEINII (DINOPHYCEAE)
Authors: Highftll Joe F. , Pfiester Lois A.
Published: January 2018

The sexual and asexual portions of the life cycle of Glenodiniopsis steinii were examined at both the light and scanning electron microscopic levels. Asexual reproduction by cell division occurs every 2 to 3 d under optimal conditions. Gamete formation and sexual reproduction can be induced by either nitrogen deprivation or aging of cultures. Fusion of gametes peaks about 10 hr into the light cycle and requires about 10 hr for completion. Cells remain motile during fusion but the zygote loses motility. The cell then undergoes changes that give it a thick‐walled, warty appearance.
POLLINATOR EFFECTIVENESS AND SEED SET IN POPULATIONS OF AGALINIS STRICTIFOLIA (SCROPHULARIACEAE)
Authors: Dieringer Gregg
Published: January 2018

Examining variation in pollinator effectiveness and seed production resulting from single pollinator visits can provide a deeper understanding of how pollinators may influence reproduction in plant populations. When comparing populations, differences in the number of seeds produced from single pollinator visits to flowers may not always be attributable to differences in pollen deposition, but rather to differences in plant fecundity or resource availability. Pollinator effectiveness and seed production were studied for two populations over a 4‐year period and were measured using single bee visit manipulations of flowers. No significant difference in pollinator effectiveness (pollen deposited on stigmas) was observed between the two populations. However, a significant difference between the two populations was observed in the number of seeds produced per flower. The Wellhouse population produced approximately three times as many seeds/flower from a single pollinator visit as did the Firefly Meadow population. Within each population, pollinators (Bombus pennsylvanicus and Apis mellifera) did not differ in the number of pollen grains deposited on stigmas or seeds produced per flower from single visit experiments. Differences in plant density, pollen viability, and ovules per flower also could not account for a significant amount of the variation. A resource augmentation experiment (water and fertilizer application) resulted in a decrease in seeds per flower per bee visit for the water treatment at the Wellhouse population only. For both populations, pollen deposition, pollen viability, and ovules per flower were unaffected by the resource augmentation. Alternative possibilities for the observed differences in seeds per flower per bee visit are discussed.
AN ANALYSIS OF VARIABILITY IN SEED SETTLING VELOCITIES OF SEVERAL WIND‐DISPERSED ASTERACEAE
Authors: Andersen Mark C.
Published: January 2018

Dispersal is an important life history component. Seed settling velocity may be a useful surrogate for the measurement of dispersal ability in wind‐dispersed plants, particularly those whose seeds have plumose dispersal structures. I measured settling velocities on seeds of eight species of Asteraceae, including annuals, biennials, and perennials, and including both native and introduced species. The species are Aster exilis, Picris echioides, Chrysopsis villosa, Heterotheca grandiflora, Conyza bonariensis, Sonchus oleraceous, Senecio vulgaris, and Taraxacum officinale. From these data I estimated components of total variation in seed settling velocities due to differences among species, among plants within species, and among inflorescences and seeds within plants. Significant amounts of variability were found at all levels. Contrasts among mean settling velocities showed that the five introduced species have lower settling velocities than the three native species; this result continues to be true when annuals are considered separately from biennials and perennials. Also, over all eight species, annuals have lower settling velocities than biennials and perennials. Variability among species apparently reflects different dispersal “strategies” employed by the species; these different strategies may be correlated with other life‐history traits and with ecological characteristics. Variability within species also may have ecological consequences in that such variability may represent an example of risk‐spreading.
EFFECT OF THE PARENTAL NUTRIENT REGIME ON GROWTH OF THE PROGENY IN ABUTILON THEOPHRASTI (MALVACEAE)
Authors: Wulff Renata D. , Bazzaz Fakhri A.
Published: January 2018

Two genets of Abutilon theophrasti were clonally replicated and grown to maturity in a glasshouse at two levels of nutrient supply. The seeds produced were weighed and the resulting seedlings exposed to two nutrient levels during development. The progeny plants were harvested on three occasions, and leaf areas and dry weights of the different plant parts were determined. At the early stages of growth an increase in the maternal nutrient supply significantly increased seedling height, cotyledon area, and leaf areas, and seed weight had a significant effect on several traits. The maternal nutrient addition had no significant effect at a later stage of growth (35 d after sowing), but at 56 d after sowing it did affect offspring leaf areas and dry weights. Significant interaction terms indicate that the response to parental nutrient addition may depend both on genotype and on the nutrient status of the progeny. Different plant characters are differentially sensitive to maternal conditions and these may be expressed at different stages of development.
CONTRASTING GERMINATION AND SEEDLING GROWTH OF BETULA ALLEGHANIENSIS AND RHUS TYPHINA SUBJECTED TO VARIOUS AMOUNTS AND TYPES OF PLANT LITTER
Authors: Peterson Chris J. , Facelli José M.
Published: January 2018

Several characteristics of the environment, such as plant litter, may interact with species characteristics, such as seed size, to determine patterns of plant establishment and thereby influence abundance and spatial location of plants long after the factor has itself disappeared. To determine if litter might differentially affect seedling establishment of Betula alleghaniensis Britton and Rhus typhina L., two woody species with different sized seeds, we conducted two greenhouse experiments. We documented emergence, morphology, and growth patterns of seedlings covered by three amounts each of Fagus grandifolia Ehrh. leaves or Tsuga canadensis L. needles. All amounts of litter significantly reduced and delayed final Betula alleghaniensis seedling emergence, and the resultant seedlings had reduced root: shoot ratios, longer hypocotyls, and were less robust. Litter did not affect Rhus typhina emergence but did alter biomass allocation: stem, leaf, and root biomass of Rhus seedlings was reduced by greater amounts of litter, and by leaf litter relative to needle litter. We attribute the different responses of Betula and Rhus to differences in seed size (Betula mean seed size = 1.0 mg; Rhus mean seed size = 8.5 mg) and germination cues (Betula requires light, Rhus requires chemical or heat scarification), and suggest that differential response to litter may contribute to coexistence among these sympatric species.
GRAVITY EFFECTS ON CELLULOSE ASSEMBLY
Authors: Brown R. Malcolm , Kudlicka Krystyna , Cousins Susan K. , Nagy Robert
Published: January 2018

The effect of microgravity on cellulose synthesis using the model system of Acetobacter xylinum was the subject of recent investigations using The National Aeronautic and Space Administration's Reduced Gravity Laboratory, a modified KC‐135 aircraft designed to produce 20 sec of microgravity during the top of a parabolic dive. Approximately 40 parabolas were executed per mission, and a period of 2 g was integral to the pullout phase of each parabola. Cellulose biosynthesis was initiated on agar surfaces, liquid growth medium, and buffered glucose during parabolic flight and terminated with 2.0% sodium azide or 50.0% ethanol. While careful ground and in‐flight controls indicated normal, compact ribbons of microbial cellulose, data from five different flights consistently showed that during progression into the parabola regime, the cellulose ribbons became splayed. This observation suggests that some element of the parabola (the 20 sec microgravity phase, the 20 sec 2 g phase, or a combination of both) was responsible for this effect. Presumably the cellulose I α crystalline polymorph normally is produced under strain, and the microgravity/hypergravity combination may relieve this stress to produce splayed ribbons. An in‐flight video microscopy analysis of bacterial motions during a parabolic series demonstrated that the bacteria continue to synthesize cellulose during all phases of the parabolic series. Thus, the splaying may be a reflection of a more subtle alteration such as reduction of intermicrofibrillar hydrogen bonding. Long‐term microgravity exposures during spaceflight will be necessary to fully understand the cellulose alterations from the short‐term microgravity experiments.
TIME‐LAPSE ANALYSIS OF GRAVITROPISM IN CERATODON PROTONEMATA
Authors: Young J. C. , Sack F. D.
Published: January 2018

The tip cell of the protonema of the moss Ceratodon purpureus (Hedw.) Brid. is negatively gravitropic when grown in the dark on supplemented agar. Gravitropism, plastid distribution, and plastid movement were studied in living cells using time‐lapse video microscopy and infrared light. A wrong‐way (downward) curvature preceded upward curvature and was detected as early as 2 minutes after reorientation. Upward curvature began 30–45 minutes after reorientation to the horizontal. Cell division temporarily reversed upward curvature, but did not inhibit wrong‐way curvature. Since significant amyloplast sedimentation always occurred before the start of upward curvature, it is possible that these amyloplasts function as statoliths for upward curvature. However, no significant amyloplast sedimentation occurred before wrong‐way curvature. Thus, this early phase of gravitropism cannot require plastid sedimentation for gravity sensing. Most plastids moved within and between zones, and plastid zonation was highly dynamic. Plastids moved toward the apex and toward the base of the cell at rates much slower than cytoplasmic streaming. Despite the dynamic nature of plastid movement and zonation, during upward curvature the distance between sedimented plastids and the apex stayed constant. Time‐lapse analysis has revealed intriguing events not readily seen previously using destructive sampling.
MUSOPSIS N. GEN.: A BANANA‐LIKE LEAF GENUS FROM THE EARLY TERTIARY OF EASTERN NORTH GREENLAND
Authors: Boyd Austin
Published: January 2018

A fossil flora from the Late Paleocene‐Early Eocene Thyra Ø Formation of eastern North Greenland (paleolatitude 77° N) has yielded monocotyledon leaf impressions with characters seen only in the closely related modem species in the families of Heliconiaceae, Musaceae, and Strelitziaceae. The combination of large costae widths and parallel, nonanastomosing, lateral veins that depart at right angles from the costae in the fossil material are features present only in leaves of extant species from these families. Three basic venation patterns also are recognized in the modem species of these families, but except for the generaStrelitziaandPhenakospermum, none of these patterns are present exclusively in any one family.Musopsisn. gen. is created for the fossil material from Greenland, but it is considered a form genus due to the lack of gross morphological features that can be used for separating leaves of the modem genera in Heliconiaceae, Musaceae, and Strelitiziaceae. It is the first known Arctic occurrence of fossil leaf material resembling this modem group of taxa.
SEEDS OF KOSTELETZKYA VIRGINICA (MALVACEAE): THEIR STRUCTURE, GERMINATION, AND SALT TOLERANCE. I. SEED STRUCTURE AND GERMINATION
Authors: Poljakoff‐Mayber A. , Somers G. F. , Werker E. , Gallagher J. L.
Published: January 2018

Dormancy of Kosteletzkya virginica (L.) Presl. seeds is primarily due to the impermeability of the seed coat to water. The impermeable structure is assumed to be, in other Malvaceae, the palisade layer of the seed coat. The percentage of seeds capable of imbibition and germination increased with increasing time of storage at low temperatures, but the release from dormancy was not accompanied by decreased seed coat resistance to pressure. Under natural conditions, mechanical damage to the seed coat due to changes in temperature and/or abrasion may render the seeds water permeable. It is not clear what causes water permeability during storage under laboratory conditions. During seed maturation and drying, the inner epidermis of the tegmen partly separates from the rest of the seed coat and an air space, which makes the seed buoyant, is formed around the region of the chalazal cleft. The optimal temperature for germination of K. virginica seeds is between 28 and 30 C in light or darkness.