bluuebunny/crossref_metadata_2025 huggingface dataset:
DEVELOPMENT OF STOMATA IN SELAGINELLA: DIVISION POLARITY AND PLASTID MOVEMENTS
Authors: Brown Roy C. , Lemmon Betty E.
Published: January 2018

The young guard cell of Selaginella inherits a single plastid from the division of the stomatal guard mother cell (GMC). During early stomatal development the single plastid undergoes a complex series of migrations and divisions. The regular pattern of plastid behavior appears to be an expression of the genetic program controlling division plane and cytomorphogenesis. The plastid in the GMC becomes precisely aligned with its midconstriction intersected by the plane of a preprophase band of microtubules (PPB) oriented parallel to the long axis of the leaf. This alignment with respect to the future division plane of the cytoplasm ensures equal plastid distribution to the daughter cells. Cytokinesis occurs in the plane previously marked by the PPB and the plastid in each daughter cell lies between the lateral wall and the newly formed nucleus. Following cytokinesis the plastid in each young guard cell develops a median constriction and migrates to the common ventral wall where the isthmus is associated with a system of microtubules in the vicinity of the developing pore region. Plastid division is completed while the plastid is adjacent to the common ventral wall. Following division, the two daughter plastids move back toward the lateral wall. Each plastid may divide again during guard cell maturation but no further migrations occur.
ULTRASTRUCTURE OF CARPOSPOROPHYTE DEVELOPMENT IN THE RED ALGA GLOIOSIPHONIA VERTICILLARIS (CRYPTONEMIALES, GLOIOSIPHONIACEAE)
Authors: Delivopoulos Stylianos G. , Kugrens Paul
Published: January 2018

The ultrastructure of carposporophyte development is described for the red algaGloiosiphonia verticillarisFarl. The auxiliary cell produces gonimoblast initials, which divide to produce two types of gonimoblast cells—the nondividing vacuolate cells and terminal generative gonimoblast cells. The generative gonimoblast cells form clusters of carpospore initials, which eventually differentiate into carpospores. After gonimoblast filaments are formed, the auxiliary cell undergoes autolysis, causing degeneration of septal plugs between the auxiliary cell and adjacent cells, thus forming a fusion cell. Since this cell lacks starch and appears degenerate throughout carposporophyte development, a nutritive function cannot be ascribed to the fusion cell. Carpospore differentiation is simple and proceeds through three developmental stages. Young carpospores structurally resemble gonimoblast cells, because they contain undeveloped plastids, large quantities of floridean starch, and are surrounded by extensive mucilage instead of a distinct wall. In addition, dictyosomes form and begin to produce vesicles with fibrous contents representing carpospore wall material. During the intermediate stage, dictyosomes continue to produce vesicles that contribute additional carpospore wall material, thereby compressing the mucilage and creating a darker‐staining layer outside the carpospore wall. Plastids form internal thylakoids by invaginations of the inner membrane of the peripheral thylakoid. The endoplasmic reticulum forms large granular vacuoles that appear to be degraded during subsequent stages of development. Mature carpospores form cored vesicles. They also contain mature chloroplasts, large amounts of floridean starch, and occasionally granular vacuoles. During this stage, interconnecting carpospore‐carpospore and carpospore‐gonimoblast cell septal plugs begin to undergo degeneration. This process may be mediated by tubular structures.
IS THE GRASS GYNOECIUM MONOCARPELLARY?
Authors: Philipson W. R.
Published: January 2018

Two interpretations are currently applied to the gynoecium of the Gramineae. Either it is monocarpellary or it is syncarpous (pseudomonocarpellary). These two views are examined and it is concluded that the grass gynoecium retains features of a tricarpellary ancestry. This conclusion is reached principally on the basis of comparison with the gynoecia of the family Restionaceae.
LOCALIZATION OF STARCH BIOSYNTHETIC AND DEGRADATIVE ENZYMES IN MAIZE LEAVES
Authors: Echeverria Edgardo , Boyer Charles D.
Published: January 2018

The cellular distribution of the starch biosynthetic and degradative enzymes in protoplasts prepared from maize leaf mesophyll and bundle sheath cells was investigated. In conformity with the cellular distribution of starch, starch biosynthetic enzymes (soluble starch synthase, ADPglucose pyrophosphorylase, branching enzyme and starch Phosphorylase) were exclusively localized in the bundle sheath cells. In contrast, starch degradative enzymes (α‐amylase, β‐amylase and debranching enzyme) were present in both types of leaf cells. Isolated chloroplasts from bundle sheath cells were shown to contain 100% of the starch biosynthetic enzymes. However, approximately 60% of the activity of degradative enzymes and 67% of the activity of starch Phosphorylase was localized in bundle sheath chloroplasts.
RELATIVE SALT TOLERANCE OF CAKILE EDENTULA (BRASSICACEAE) FROM LACUSTRINE AND MARINE BEACHES
Authors: Boyd Robert S. , Barbour Michael G.
Published: January 2018

Seeds of Cakile edentula ssp. edentula var. edentula (hereafter edentula) were collected from the Pacific Ocean shore of Washington, and Cakile edentula ssp. edentula var. lacustris (hereafter lacustris) seeds were collected from the Lake Huron shore of Ontario. Germination rates of the two varieties showed equal tolerance of substrate salinities ranging from 0–10,000 ppm. Early root growth of edentula seedlings was significantly stimulated by 1,000 ppm salts, but otherwise both varieties showed equal tolerance to 10,000 ppm. Edentula plants exposed for 4 wk to salt spray intensities of 0, 20, and 90 mg dm–2 d–1, applied in a growth chamber environment, showed no significant changes in shoot or root biomass, plant morphology, or reproductive effort. Lacustris plants exhibited significant declines in stem length and reproductive effort with increasing levels of salt spray. Our results suggest that lacustris and edentula have diverged physiologically over the past 9,000 years, and field observations from the literature corroborate our conclusion that this divergence in salt tolerance has ecological significance.
POLLINATION, FERTILIZATION AND OVULE ABORTION IN OXALIS MAGNIFICA
Authors: Guth Christine J. , Weller Stephen G.
Published: January 2018

Pollination, fertilization and ovule abortion were studied in Oxalis magnifica (Rose) Knuth, a strongly self‐incompatible herb that regularly matures only a fraction of its ovules. Examination of cleared ovules indicated that among 9 individuals the average number of ovules fertilized ranged from 48–92%. The remaining ovules either failed to produce female gametophytes, or more commonly contained unfertilized female gametophytes, despite large numbers of compatible pollen grains that were placed on stigmas. Abortion of fertlized ovules could be detected first by the flattened and enlarged appearance of the endosperm nuclei, followed by visible deterioration of the embryo. Among individuals the rate of embryo abortion varied from 3.4–47.9%. At lower levels of pollination an almost one‐to‐one relationship existed between the number of pollen grains placed on stigmas and the number of seeds matured in the capsule. No threshold number of pollen grains necessary for successful pollen tube growth and fertilization could be demonstrated. Reduction in seed number through embryo abortion provides an opportunity for selection among developing seeds. The potential for this form of selection varies widely among individuals of Oxalis magnifica, which showed a 14‐fold variation in the average percentage of aborted ovules.
TWO‐DIMENSIONAL SPREADS OF SYNAPTONEMAL COMPLEXES FROM SOLANACEOUS PLANTS. II. SYNAPSIS IN LYCOPERSICON ESCULENTUM (TOMATO)
Authors: Stack Stephen M. , Anderson Lorinda K.
Published: January 2018

Synapsis in tomato (Lycopersicon esculentum, 2n = 24) pollen mother cells (PMCs) was examined using a hypotonic bursting technique along with squashing and partial three‐dimensional reconstructions from serial thin sections. Tomato has all the meiotic stages expected from classical descriptions of meiosis. Based on observed synchrony of PMCs within anthers and between anthers of a bud, leptotene through pachytene was estimated to last 24 hr. The hypotonic bursting technique disperses most protoplasm including chromatin to reveal components of synaptonemal complexes (SCs) in two dimensions. Leptotene chromosomes have single axial cores that sometimes show presynaptic alignment and associate with polycomplexes. Zygotene chromosomes contain segments of SCs and axial cores that may be associated with polycomplexes. Axial cores often show presynaptic alignment in zygotene. Synapsis tends to be initiated toward the ends of chromosomes, but interstitial initiation occurs as well. Typically synapsis occurs last in pericentromeric heterochromatin. Recombination nodules (RNs) are numerous on zygotene SCs, indicating the process of recombination probably starts at this time. Zygotene RNs can occur on either face of the central element of SCs. In pachytene, SCs are formed throughout the length of bivalents. Telomeres are visible at synapsed ends, and kinetochores develop as prominent structures by late pachytene. In early pachytene there appears to be a precipitous loss of RNs that typically leaves only one or two RNs per SC. These RNs may lie at the sites of reciprocal recombination events. In the diffuse stage, desynapsis begins with separation of lateral elements distally and/or near kinetochores. Polycomplexes often form at these early sites of desynapsis. Desynapsis appears to be progressive but is temporarily inhibited at telomeres, RNs, and kinetochores. By the end of the diffuse stage, lateral elements have separated completely and have begun to fragment. At the beginning of diplotene, components of SCs are no longer visible.
NEW INTERGENOMIC HYBRIDS AMONG SOME AFRICAN DIPLOID SPECIES OF HIBISCUS SECT. FURCARIA
Authors: Menzel Margaret Y. , Richmond Kenneth L. , Contolini Carol S. , Huang Peikun
Published: January 2018

Chromosome pairing was examined at Metaphase 1 in F1 hybrids between Hibiscus surattensis L. (B genome) and three other diploid species, H. hiernianus Exell, H. mastersianus Hiern, and H. mechowii Garcke. The low level of chromosome association in all three types of hybrids indicated that the pollen parent of each hybrid contributed a genome that was meiotically nonhomologous with B. Earlier studies had shown that H. mastersianus and H. hiernianus have similar genomes that are nonhomologous with the genome of H. mechowii. Thus, these four African diploids with overlapping ranges encompass three different genome groups. Provisional genome designations were assigned as follows: H. hiernianus, Xhie; H. mastersianus, Xmas; H. mechowii, Ymec.
AUTOPOLYPLOIDY IN TOLMIEA MENZIESII (SAXIFRAGACEAE): GENETIC INSIGHTS FROM ENZYME ELECTROPHORESIS
Authors: Soltis Douglas E. , Rieseberg Loren H.
Published: January 2018

Despite over 30 years of speculation, the genetic consequences of autopolyploid speciation are largely unknown. Evidence from several sources indicates that Tolmiea menziesii is one of the best documented examples of autopolyploidy in natural populations. As such, Tolmiea can serve as a model for providing insights into autopolyploid speciation. Data from enzyme electrophoresis indicate that tetrasomic inheritance operates in tetraploid Tolmiea. These data indicate that a chromosome can pair with any of its three homologous chromosomes. For all polymorphic loci, heterozygosity is substantially higher in tetraploid Tolmiea compared to the diploid cytotype. Furthermore, individual tetraploid plants can maintain as many as three or four alleles at a single locus. Enzyme multiplicity was also observed in tetraploid Tolmiea. For the dimeric enzyme PGI, individual tetraploid plants were identified at Pgi‐2 that maintained three alleles, resulting in the production of six different enzymes. Although these genetic consequences of autopolyploidy had been predicted, they have not been previously demonstrated for an autotetraploid in nature. The increased heterozygosity and enzyme multiplicity observed may afford an autopolyploid greater genetic and biochemical versatility relative to its diploid progenitor. These findings suggest that tetrasomic inheritance provides a genetic avenue through which autopolyploid speciation can successfully occur.
AERODYNAMICS OF EPHEDRA TRIFURCA: I. POLLEN GRAIN VELOCITY FIELDS AROUND STEMS BEARING OVULES
Authors: Niklas Karl J. , Buchmann Stephen L. , Kerchner Vincent
Published: January 2018

The behavior of pollen grains within the airspace around Ephedra trifurca is described. Vectoral analyses of pollen grains moving around stems and ovules indicate a complex pattern of directional and magnitudinal changes in trajectories that can be related to the geometries of surfaces that obstruct airflow. Pollen grains, passing around cylindrical stems oriented normal to the direction of ambient airflow, are deflected in circumrotating non‐laminar flow‐patterns. Stems tilted downwind deflect pollen grains into trajectories along leeward surfaces of stems. These trajectories travel acropetally in a spiraling pattern and may intersect airflow patterns created around and by ovules. Computer analyses of pollen motion in the vicinity of ovules indicate that pollen vector‐direction is highly canalized and directed toward micropyles. Within the immediate vicinity of micropyles, which produce pollination droplets, analyses indicate that the magnitudinal variance of pollen grain vectors is high (spanning three orders of magnitude). This variance coincides with dramatic changes in the local Reynolds numbers, resulting in a localized region around the micropyle in which neither viscous nor inertial forces predominate. Based on additional aerodynamics parameters (vector curl, vector‐divergence, and vector curl‐differential) it is shown that the region around the pollination‐droplet is characteristically a “pollen sink” (pollen grains collect in this airspace) in which abrupt changes can occur in the angular momenta of airborne pollen grains. These aerodynamic analyses suggest that the morphology of ovules and the stems to which they are attached facilitates pollen capture by creating an aerodynamic “singularity” (= a unique region) around the pollination‐droplet.
TUBULAR CAVITIES IN WHITE SNAKEROOT, EUPATORIUM RUGOSUM (ASTERACEAE)
Authors: Lersten Nels R. , Curtis John D.
Published: January 2018

Oil‐filled schizogenous cavities 0.2‐3.0 mm in length, each with a uniseriate epithelium, occur in all organs of white snakeroot (Eupatorium rugosum). Some epithelial cells swell, thus shrinking or occluding the cavity lumen. Foliar cavities form in staggered files in the midrib and in association with major veins. Cavities are progressively smaller and sparser in successive vein orders; the smallest ones develop as transformed bundle sheath cells in minor veins. Cavities in stems occur in irregular vertical files near vascular bundles in both cortex and pith. Leaf and stem cavities elongate variously, depending on when and where they form; in roots and floral organs, however, cavities are always short and sparse except in bracts, where they are common. Since each cavity remains discrete, we call these internal spaces ‘tubular cavities’ rather than ‘ducts’, which have generally been vaguely defined.
VARIATION IN POPULATION GROWTH RATE IN THE WOODLAND ANNUAL IMPATIENS PALLIDA (BALSAMINACEAE)
Authors: Cid‐Benevento Carmen R. , Schaal Barbara A.
Published: January 2018

Variation in population growth rate over environmental gradients was determined for the annual Impatiens pallida (Balsaminaceae), by monitoring age‐ and size‐specific survivorship and fecundity in five populations of this summer‐flowering and primarily woodland species. All I. pallida seedlings emerged within a few days of each other and a size hierarchy was established within a month, and remained unchanged thereafter. Light and initial seedling density together explained 67% of the variance in mean adult plant size. As a result of differences among populations in the amount of disturbance, survivorship to the time of floral bud production ranged from 39% to 93% of the initial seedling total. Survivorship during the reproductive period was most affected by plant size and soil moisture. For plants surviving to flowering time, the probability of setting seed, the type of seed and the number of seeds produced per plant were significantly positively correlated with plant size. More than 82% of all seeds were produced by plants greater than or 1 m tall. Cleistogamy was the major form of reproduction in 4 out of 5 populations monitored. The net reproductive rate (R0) differed greatly among populations, ranging from 1.23 to 16.27. Population growth rate increased with increasing resource availability and decreasing disturbance during the growing season. The magnitude of R0 depended primarily on 1) timing, intensity and frequency of disturbance, 2) length of the reproductive period, and 3) population size structure.
EVIDENCE OF SIMPLE POLYEMBRYONY IN PERMIAN SEEDS FROM ANTARCTICA
Authors: Smoot Edith L. , Taylor Thomas N.
Published: January 2018

Well‐preserved seeds with multiple embryos are described from the Permian of the Beardmore Glacier region, Antarctica. The seeds are platyspermic, winged and contain two archegonia in the micropylar end. Each archegonium contains an undifferentiated, multicellular embryo at a comparable stage of development. Attached to one end of each embryo is an elongate structure similar to the suspensor in extant gymnosperms. This discovery represents the earliest example of simple polyembryony yet recorded from the fossil record.
FLORAL DEVELOPMENT IN MYRISTICA (MYRISTICACEAE)
Authors: Armstrong Joseph E. , Tucker Shirley C.
Published: January 2018

Myristica fragrans and M. malabarica are dioecious. Both staminate and pistillate plants produce axillary flowering structures. Each pistillate flower is solitary, borne terminally on a short, second‐order shoot that bears a pair of ephemeral bracts. Each staminate inflorescence similarly produces a terminal flower and, usually, a third‐order, racemose axis in the axil of each pair of bracts. Each flower on these indeterminate axes is in the axil of a bract. On the abaxial side immediately below the perianth, each flower has a bracteole, which is produced by the floral apex. Three tepal primordia are initiated on the margins of the floral apex in an acyclic pattern. Subsequent intercalary growth produces a perianth tube. Alternate with the tepals, three anther primordia arise on the margins of a broadened floral apex in an acyclic or helical pattern. Usually two more anther primordia arise adjacent to each of the first three primordia, producing a total of nine primordia. At this stage the floral apex begins to lose its meristematic appearance, but the residuum persists. Intercalary growth below the floral apex produces a columnar receptacle. The anther primordia remain adnate to the receptacle and grow longitudinally as the receptacle elongates. Each primordium develops into an anther with two pairs of septate, elongate microsporangia. In pistillate flowers, a carpel primordium encircles the floral apex eventually producing an ascidiate carpel with a cleft on the oblique apex and upper adaxial wall. The floral ontogeny supports the morphological interpretation of myristicaceous flowers as trimerous with either four‐sporangiate anthers or monocarpellate pistils.
EARLY ANGIOSPERM REPRODUCTION: CALODA DELEVORYANA GEN. ET SP. NOV., A NEW FRUCTIFICATION FROM THE DAKOTA FORMATION (CENOMANIAN) OF KANSAS
Authors: Dilcher David L. , Kovach Warren L.
Published: January 2018

A new angiosperm fructification, Caloda delevoryana, is described from the Cenomanian age Dakota Formation of central Kansas. It consists of a long, narrow, main axis with numerous secondary axes arranged helically around the main axis. These secondary axes are each terminated in a small receptacle bearing numerous conduplicate carpels. No evidence of a perianth or androecium was found. This fructification bears some similarity to a number of different modern orders, such as the Hamamelidales, Alismatales, Najadales, and Piperales, and families, particularly the Platanaceae and the Aponogetonaceae, but cannot definitely be assigned to any modern taxon within the angiosperms. C. delevoryana exhibits several characters traditionally assumed to be primitive in the angiosperms, and several other features of this fossil are proposed as primitive in the evolution of angiosperms. This floral axis, with its compact mass of numerous secondary axes bearing very small fruits and seeds, may be the product of reduction through diminished growth of internodes and carpels, and elaboration through increased repetition of floral modules. This record adds to the rapidly growing body of paleobotanical data on early angiosperm reproductive structures, which should prove important in the assessment of the extent and direction of angiosperm evolution.
FLORAL STRUCTURE AND ORGANOGENESIS IN PODOPHYLLUM PELTATUM (BERBERIDACEAE)
Authors: DeMaggio Augustus E. , Wilson Carl L.
Published: January 2018

The life cycle of Podophyllum can be divided into two phases, a subterranean phase during which a conspicuous winter mixed terminal bud forms at the end of a rhizome, and an aerial phase, during which the primordia of the structures within the winter bud give rise the next spring to an aerial shoot composed of a stem, 2 leaves, and a single flower. The transition from a vegetative to a floral apex occurs at the end of July, when the apical meristem becomes a globoid structure. During the first and second weeks of August, the floral organs are laid down along the sides of an elongated floral apex. The order of initiation of the floral organs is sepals, petals, stamens, gynoecium, and stamens. Petal primordia are initiated in early August, but growth ceases after they attain a height of about 2 mm. This inhibition persists until the middle of May in the next growing season, when the petals grow to 12 mm within 2 weeks. At anthesis the petals have enlarged to a length of 2 cm or more. The gynoecium is usually composed of a single terminal carpel. The ovules are chiefly supplied by branches from a ventral bundle complex, but that is supplemented by medullary bundles that are formed in the base of the gynoecium, below the loculus. It could be argued that these medullary bundles are surviving remnants of the vascular supply to a second carpel, no longer extant. A transmitting tract extends from the stigma about half the distance to the loculus. The tract is lined with unicellular glandular cells and is open from the stigma to the loculus.
EXCEPTIONAL GENETIC DIVERGENCE OF NORTHERN FLINT CORN
Authors: Doebley John F. , Goodman or M. , Stuber Charles W.
Published: January 2018

Isozyme analysis of 18 Northern Flint populations supports the previously published hypothesis that Northern Flint was derived from maize races of the southwestern U.S. and northwestern Mexico. Isozyme data also show that during its short evolutionary history (approx. 1,000 yr) Northern Flint obtained a degree of genetic differentiation from other North American maize landraces more typical of a separate species than of landraces of the same cultigen. Genetic drift, changes in selection pressure associated with movement into a new environment, and reproductive isolation from other maize races may have contributed to the genetic dissimilarity of Northern Flint.
GYNOECIAL DEVELOPMENT, POLLINATION, AND THE PATH OF POLLEN TUBE GROWTH IN THE TEPARY BEAN, PHASEOLUS ACUTIFOLIUS
Authors: Lord Elizabeth M. , Kohorn Loraine U.
Published: January 2018

The gynoecium of Phaseolus acutifolius var. latifolius, a self‐compatible legume, is characterized by a wet non‐papillate stigma, an intermeditae hollow/solid style type, and secretory cells on the ventral surface of the ovary which direct pollen tube growth. The stigma is initially receptive 5–6 days prior to anthesis. Production of stigmatic secretions, composed primarily of carbohydrates and lipids, fragment the cuticle covering epidermal cells of the stigma early in ontogeny; the lipidic aspect of the copious secretions apparently serves to inhibit desiccation after the cuticle is ruptured. Stylar canal development occurs as a combination of elongation of a basal canal present early in development, and dissolution of part of a solid transmitting tract tissue just below the stigma. Anthers dehisce and the tricolporate pollen is released onto the receptive stigma one day before anthesis. Following initial growth in intercellular spaces in the transmitting tract of the stigma, pollen tubes adhere to epidermal secretory cells along the ventral side of the stylar canal and upper ovary; here the transmitting tract is apparently limited in the number of tubes it can accommodate, providing a possible site of selection of male gametes.
DEVELOPMENT OF BICELLULAR FOLIAR SECRETORY CAVITIES IN WHITE SNAKEROOT, EUPATORIUM RUGOSUM (ASTERACEAE)
Authors: Curtis John D. , Lersten Nels R.
Published: January 2018

Bicellular secretory cavities in Eupatorium rugosum occur only in foliar mesophyll, distributed uniformly from leaf tip to base, with a mean density of 450 per mm2. They are absent from petiole and all other vegetative and floral organs. Each cavity contains an oily droplet, which is surrounded by two cup‐shaped cells. An initial cell divides into two equal cavity cells with their shared wall always perpendicular to the epidermis. After vacuoles form, each protoplast retracts from the other and deposits a new, callosic wall around the cavity, and a thicker callose deposit on the remaining shared walls outside of the cavity. The original shared wall remains intact across the cavity until maturity. It is pulled taut by cavity cell growth and restricts further expansion except in one paradermal direction. Later, this shared wall disappears from the cavity. An oily fluid of unknown composition is secreted into the enlarging cavity. Because bicellular cavities develop neither lysigenously nor in true schizogenous fashion, we propose the term “pseudoschizogeny” for this type of development. Unusual, or perhaps unique, features of this cavity: bicellular condition, protoplast retraction from the common shared wall, and deposition of a callose wall. Preliminary results of a survey of Eupatorium show that bicellular cavities are uncommon but widely distributed geographically.
PHYLOGENETIC IMPLICATIONS OF DIVERSE SEED TYPES, CHROMOSOME NUMBERS, AND POLLEN MORPHOLOGY IN HOUSTONIA (RUBIACEAE)
Authors: Terrell Edward E. , Lewis Walter H. , Robinson Harold , Nowicke Joan W.
Published: January 2018

Seed and pollen morphology were studied by light microscopy and scanning electron microscopy in 39 North and Central American species of Houstonia (including Hedyotis, but excluding Oldenlandia). Chromosome counts were obtained for eight taxa, of which five lacked previous chromosome data. A chromosome number of n = 17 for Houstonia gracilis is a new base number for the genus. Seed external morphology in the genus is very diverse, including variation in compression, margins, testa surfaces, and elaboration of ventral cavities or depressions and hilar ridges or their absence. Three types of pollen apertures are recognized: colporate with type A os, colpororate, and colporate with type B os, the last the most advanced type, occurring in H. caerulea and related species. The 39 species are arranged in twelve groups, based on correlation of seed, pollen, and chromosome data. Geographic distribution provides supplementary evidence for the distinctness and integrity of the six principal groups each composed of 2–9 species. Five of the six minor groups each with one species need chromosome data to facilitate future taxonomic decisions. Chromosome numbers of x = 6, 7, 8, 9, 10, 11, 13, and 17 are now known in this genus, and phylogenetic implications of the combined data are discussed.
SEASONAL PATTERNS OF LEAF PHOTOSYNTHETIC CAPACITY IN SUCCESSIONAL NORTHERN HARDWOOD TREE SPECIES
Authors: Jurik Thomas W.
Published: January 2018

Seasonal patterns of leaf photosynthetic capacity and conductance were determined for deciduous hardwood tree species in natural habitats in northern lower Michigan. Leaves of bigtooth aspen and red oak at the top of the canopy had higher maximum CO2 Exchange Rate (CER) (10–15 μmol m 2 s 1) than leaves of sugar maple, red maple, red oak, and beech growing in the understory (4–5 μmol m 2 s 1). In all leaves, CER measured at light‐saturation increased to a maximum near the completion of leaf expansion in early June, was constant until mid‐September, and then rapidly declined until leaf death. A similar pattern was seen for CER measured in low light (1.5% full sun). Respiration rate in the dark was highest in young leaves and decreased during leaf expansion; a relatively constant rate was then maintained for the rest of leaf lifespan. The seasonal pattern of the initial slope of the light response of CER paralleled the pattern of light‐saturated CER. The initial slope in midsummer ranged from values of 37 to 44 μmol/mol for species in the understory to 51 and 56 μmol/mol for red oak and bigtooth aspen, respectively, at the top of the canopy. Leaf conductance was constant throughout most of leaf lifespan, with some decline occurring in autumn. Leaves at the top of the canopy had higher conductances for water vapor (2–5 mm/s) than leaves in the understory (1–2 mm/s). All species maintained leaf intercellular CO, mole fractions (c,) near 200 uML/L until autumn, when c, increased during leaf senescence.
INTERCONNECTED REPRODUCTIVE AND VEGETATIVE REMAINS OF POPULUS (SALICACEAE) FROM THE MIDDLE EOCENE GREEN RIVER FORMATION, NORTHEASTERN UTAH
Authors: Manchester Steven R. , Dilcher David L. , Tidwell William D.
Published: January 2018

A new specimen from the Middle Eocene Evacuation Creek Member of the Green River Formation in northeastern Utah shows a twig with several leaves of Populus wilmattae Cockrell and a fruiting raceme attached. This specimen establishes for the first time the type of fruits borne by P. wilmattae and provides additional characters with which to assess its taxonomic and evolutionary status. An associated seed shows attached placental hairs like those of extant species of Populus. The Green River fossil differs from extant Populus species in having basically palmate leaf venation and in bearing its fruiting axis on a young twig. In other aspects, the fossil species is remarkably similar to the extant species Populus mexicana.
RELATIVE POLLINATOR EFFECTIVENESS AND EVOLUTION OF FLORAL TRAITS IN SPATHIPHYLLUM FRIEDRICHSTHALII (ARACEAE)
Authors: Montalvo Arlee M. , Ackerman James D.
Published: January 2018

We studied the relative effectiveness of different pollinators of Spathiphyllum friedrichsthalii Schott for 15 months on Barro Colorado Island, Panama. Pollen‐foraging stingless bees (Apidae: Trigona) made 87% of floral visits. Experiments showed that these bees pollinate flowers, and correlations of fruit‐ and seed‐set with visitation frequencies and floral contact times suggested that they were responsible for the majority of seeds produced. Fifteen species of fragrance‐foraging, male euglossine bees (Apidae: Euglossini) collectively accounted for a small portion of seed‐set in fewer than 27% of the inflorescences. Neocorynura (Halictidae) were pollen thieves and were unimportant as pollinators.

We propose that euglossine and stingless bees differentially influence outcrossing rates and the evolution of floral traits of S. friedrichsthalii. Foraging behavior of male euglossines should allow for more long‐distance pollen flow whereas stingless bees are likely to promote near‐neighbor and geitonogamous pollinations. We discuss why the prolonged male phase of anthesis in this protogynous species may be maintained through pollination by stingless bees rather than male euglossines. Furthermore, although the floral fragrance is attractive to many species of male euglossines, it attracts few individuals. This condition may represent an intermediate step in the evolution of predominant pollination by male euglossines.
SPATIAL DISTRIBUTION AND DEVELOPMENT OF ROOT SPROUTS IN FAGUS GRANDIFOLIA (FAGACEAE)
Authors: Jones Robert H. , Raynal Dudley J.
Published: January 2018

Root sprouts around 31 Fagus grandifolia parent trees, some declining due to beech bark disease, were studied to describe the pattern of sprout distribution, the ecological importance of this pattern, and the relationship between sprout patterns and parent vigor. Microtome sections of roots were studied to determine the histological origin of sprouts. Sprout distribution was circular and usually centered on the parent tree. Most sprouts were within 8 m of the parent and remained attached to the parent root system even after the sprouts reached 10 yrs of age. Root sprouting in F. grandifolia may be effective in replacing dead parent trees, but the potential for clones to spread is limited. Spatial distribution of sprouts was mostly unaffected by tree vigor. Root sprouts originated from callus tissues associated with wounds on superficial woody roots.
LIGHT EFFECTS ON LEAF MORPHOLOGY IN WATER HYACINTH (EICHHORNIA CRASSIPES)
Authors: Richards Jennifer H. , Lee David W.
Published: January 2018

Water hyacinth leaves in natural populations vary from being long and thin‐petioled to being short with inflated petioles. A variety of factors has been used experimentally to alter water hyacinth leaf shape, but what controls the development of leaf morphology in the field has not been established. We measured photosynthetic photon flux density (PPFD) and spectral distribution of radiation in a natural water hyacinth population. PPFD in the center of the water hyacinth mat was reduced to 2.7% of full sunlight, and the red to far red (R:FR) ratio was reduced to 0.28. When shoot tips of plants were exposed to artificial light environments, only plants in the treatment with a R:FR ratio comparable to that in the natural population produced leaves with long, thin petioles. Shoot tips in full sun or covered with clear plastic bags or bags that reduced light quantity without greatly altering light quality produced shorter leaves with inflated petioles. We hypothesize that the altered light quality inside a mat is a major environmental control of water hyacinth leaf morphology.
A NEW SPECIES OF MAIANTHEMUM (LILIACEAE) FROM COSTA RICA WITH AN UPRIGHT AND AERIAL RHIZOME
Authors: LaFrankie James V.
Published: January 2018

A new species of Maianthemum (Liliaceae) was discovered in a tropical montane bog at an elevation of 2,500 m in central Costa Rica. The leaf bearing stems and inflorescences are supported by a stiff, erect, branching sympodium that consists of the persistent lower portions of older shoots. This lower portion corresponds in morphology and anatomy to the horizontal subterranean rhizome that is characteristic of all previously described species of Maianthemum. An erect woody habit is rare in the Lily family; an upright aerial rhizome is unique within the genus.
INCOMPLETE ABSCISSION OF NEEDLE CLUSTERS AND RESIN RELEASE FROM ARTIFICIALLY WATER‐STRESSED LOBLOLLY PINE (PINUS TAEDA): A COMPONENT FOR PLANT‐ANIMAL INTERACTIONS
Authors: Heikkenen Herman J. , Scheckler Stephen E. , Egan Peter J. J. , Williams Carroll B.
Published: January 2018

A selected Pinus taeda L. tree was rapidly and permanently water‐stressed by severing and sealing the bole and observed daily for seven wk and then weekly for six months. Insects were captured before and during treatment from the stressed and adjacent control trees. Tissue samples were extracted at selected intervals for comparison of the stressed and control trees. Drying of the crown of the stressed tree commenced immediately. By the tenth day the previous yrs' needle clusters were red and dropping from the tree while the current yr's needle clusters remained green and did not fall. By the eleventh day beads of resin, predominantly α‐ and β‐pinene, formed and dripped from the abscission scars of the youngest needle clusters of the previous yr. At this time and for several days thereafter, insects were attracted to the stressed tree. Microscopy of abscission sites of the stressed and control trees shows that the sites where resin flowed had incomplete abscission layers, lysigenous collapse of adjacent cortical cells to form a cavity that coalesced the resin ducts associated with the needle cluster, and had mechanically ruptured the tissue connections so that resin normally contained within the duct system was released to the exterior of the tree. Volatilized α‐pinene is attractive to the insects associated with pines. Failure of abscission in the stressed tree leading to abnormal resin release is thus proposed as a means by which insects are attracted to stressed trees.
ROLE OF GROWTH SUBSTANCES IN THE FILAMENT GROWTH OF FUCHSIA HYBRIDA CV “BRILLIANT”
Authors: Jones Lucille S. , Koning Ross E.
Published: January 2018

Filaments of Fuchsia hybrida cv “Brilliant” double in length within 24 hr after bud opening. Filament growth characterized by fresh wt increase and cell elongation was significantly inhibited in vitro by l‐aminocyclopropane‐l‐carboxylic acid (ACC) but was not promoted by any growth regulator tested. Ions of Co2+ blocked the inhibitive effects of ACC in vitro suggesting that ethylene produced from ACC is the growth inhibiting substance. Ethylene levels surrounding the filaments within the closed bud decreased during development, and premature opening of the sepals which released the ethylene into the atmosphere resulted in rapid filament growth. The ACC levels were found to be much higher in the anthers than the filaments. This suggests that ethylene produced from floral organs other than filaments regulates filament elongation in Fuchsia. This is the first report of filament growth which cannot be promoted by application of growth regulators but which is inhibited by ethylene.
A TEN‐YEAR RECORD OF ABOVEGROUND BIOMASS IN A KANSAS TALLGRASS PRAIRIE: EFFECTS OF FIRE AND TOPOGRAPHIC POSITION
Authors: Abrams Marc D. , Knapp Alan K. , Hulbert Lloyd C.
Published: January 2018

Measurements of mid‐season live and dead aboveground biomass are reported for a 10‐yr period (1975–84) in a northeast Kansas tallgrass prairie. Study sites included shallow, rocky upland and deep, non‐rocky lowland soils in annually burned (April) and unburned watersheds. Lowland sites had significantly greater live biomass than upland sites for both burned and unburned prairie for the 10‐yr period. Moreover, live biomass was greater on burned than unburned lowland sites, but was not significantly increased by fire on the upland sites. Averaged across upland and lowland sites, mid‐season live biomass was 422 g m–2 on annually burned and 364 g m–2 on unburned sites for the 10‐yr period. Each site had its lowest live biomass value during the severe drought year of 1980 (range = 185–299 g m–2). During the study period, live biomass was most strongly correlated with seasonal pan water evaporation (r = –0.45 to –0.82), whereas dead biomass was correlated with the previous yr's precipitation (r = 0.61 and 0.90 for upland and lowland sites, respectively). When aboveground biomass was sampled throughout the 1984 season and separated into several components, biomass of the graminoids was 40% lower, whereas that of forbs and woody plants was 200–300% greater in the unburned than in the annually burned site.
FLAVONOIDS AND FLAVONOID EVOLUTION IN FUCHSIA (ONAGRACEAE)
Authors: Averett John E. , Hahn William J. , Berry Paul E. , Raven Peter H.
Published: January 2018

A comprehensive survey of 225 populations of 80 taxa of Fuchsia showed flavonol monoglycosides, especially quercetin and kaempferol 3‐O‐glucosides, to be ubiquitous in all species examined. Flavonol diglycosides are unusual, however, and occur in just eight species in five of the nine sections of the genus. Flavone glycosides were found in only nine species belonging to five sections and are associated with primitive taxa, having been lost in more recently derived species or sections. Flavone sulphates are restricted to species of the disjunct sect. Skinnera from New Zealand. The limited presence of flavone glycosides and flavonol diglycosides in certain species can be effectively employed as chemical markers in determining the parentage of these species in fuchsia cultivars of unknown hybrid origin.
LONG‐TERM PREFORMATION OF LEAVES AND INFLORESCENCES BY A LONG‐LIVED PERENNIAL MONOCARP, FRASERA SPECIOSA (GENTIANACEAE)
Authors: Inouye David W.
Published: January 2018

In Frasera speciosa, a long‐lived monocarpic gentian from the Colorado Rocky Mountains, leaves are preformed two to three yr in advance of their appearance above ground. Initiation of a flower stalk may begin as long as three yr before it becomes fully developed during a plant's final year. Whorls of preformed leaves are initiated continuously during the growing season, but they are enlarged only once a yr, when the basal rosette emerges above ground. This pattern of development allows plants to make maximal use of the growing season. The prolonged development may be necessary for the production of an elaborate and massive flower stalk by a slow‐growing plant in a habitat with a short growing season.
SEASONAL PATTERNS IN THE BELOWGROUND BIOMASS OF SPARTINA ALTERNIFLORA (GRAMINEAE) ACROSS A TIDAL GRADIENT
Authors: Ellison Aaron M. , Bertness Mark D. , Miller Tandy
Published: January 2018

Belowground biomass of two ht forms of the salt marsh cordgrass, Spartina alterniflora, in a New England salt marsh exhibited a seasonal cycle. Biomass was highest in midsummer with no secondary peak in biomass corresponding with the autumn dieback of aboveground parts. Total annual biomass production and the maximum depth that living tissue penetrated into the substrate decreased with increasing tidal ht. Substrate characteristics (soil aeration, pH, nutrient levels) known to affect aboveground biomass of S. alterniflora also decreased with increasing tidal ht and may similarly affect belowground biomass across the same tidal gradient.
ELECTROPHORETIC EVIDENCE FOR THE ORIGIN OF FERN SPECIES BY UNREDUCED SPORES
Authors: Gastony Gerald J.
Published: January 2018

Allopolyploid speciation is well documented in the ferns, but data from enzyme electrophoresis have only recently shown that certain sexual and agamosporous taxa are autopolyploids. Autopolyploidy may arise through fertilization involving gametophytes from unreduced spores, a mechanism previously proposed to account for the origin of allopolyploid Asplenium plenum. This report assesses the ability of unreduced spores to function in the origin of polyploid fern species by using enzyme electrophoresis to test their hypothesized role in the origin of A. plenum. Six isozymes of the enzymes PGI, PGM, TPI, 6PGD, and LAP are species‐specific for the taxa proposed as parental under two competing hypotheses for the origin of this species. Electrophoretic data reject the more conventional hypothesis involving simple hybridization and agree perfectly with expectations under the more complex hypothesized origin via unreduced spores. The mechanism whereby unreduced spores have functioned in this case is no different from that by which they would function in the origin of autopolyploid taxa and may be more common in the origin of fern species than previously suspected.
AUTOTETRAPLOIDY IN HAPLOPAPPUS SPINULOSUS HYBRIDS: EVIDENCE FROM NATURAL AND SYNTHETIC TETRAPLOIDS
Authors: Hauber Donald P.
Published: January 2018

Haplopappus spinulosus (Asteraceae) is a herbaceous, perennial weed common throughout the western Great Plains of North America and includes both diploid and tetraploid populations. A number of populations in southeastern Colorado were analyzed cytogenetically and morphologically for two reasons. First, initial observations during a routine population survey showed they were morphologically intermediate between the diploid subspecies glaberrimus and spinulosus, suggesting they might have arisen via hybridization. Second, cytological examination revealed that they were tetraploid. Because there was indication of hybrid origin, it was of interest to determine whether the populations were behaving as autopolyploids or segmental allopolyploids. The distinction between these two polyploid types is not easily made since both are likely to form multivalents at meiosis, but equations derived from a model proposed by Jackson and Hauber (1982) have made it possible to determine statistically whether a tetraploid individual is behaving meiotically as an autotetraploid. Meiotic configuration frequencies at diakinesis were determined for each tetraploid plant sampled, and observed frequencies were compared to those expected for an autotetraploid having the same maximum number of chiasmata per bivalent, chiasma frequency and chromosome number. In general, the meiotic behavior of the tetraploids was no different from that expected for autoploids. The initial hypothesis that the populations were derived from hybridization was tested by a detailed cytogenetic and morphological study of the presumed parental subspecies, F, hybrids, and natural putative hybrids. The evidence supports the hypothesis that the natural autotetraploids arose from the hybridization of ssp. glaberrimus and ssp. spinulosus.
STIGMATIC POLLEN LOADS IN POPULATIONS OF PONTEDERIA CORDATA FROM THE SOUTHERN U.S.
Authors: Glover Deborah E. , Barrett Spencer C. H.
Published: January 2018

Stigmatic pollen loads were examined in four tristylous populations of Pontederia cordata from the southern U.S. to evaluate Darwin's hypothesis that floral trimorphism promotes legitimate pollination. In each population, morph frequency, pollen production, the composition of stigmatic pollen loads and seed production were estimated. Goodness‐of‐fit tests and a measure of the efficiency of legitimate pollination were employed to evaluate pollen load patterns. Results from the four populations demonstrate that the long‐styled (L) morph usually experiences legitimate pollination, whereas the mid‐styled (M) and short‐styled (S) morphs often display random pollination. However, at Taylor Road (Louisiana) all three floral morphs exhibited statistically significant levels of legitimate pollination. The size of legitimate pollen loads suggests that in populations of P. cordata tristyly may have only a minor influence on the fecundity of morphs. Two hypotheses are proposed to explain the maintenance of floral trimorphism in contemporary populations of Pontederia spp. The first assumes the polymorphism is selectively neutral; the second suggests that it contributes towards the male component of fitness by increasing the distance, and hence the number of genets, that pollen can be transported to by pollinators. In clonal species, such as Pontederia cordata, where geitonogamous pollinations are promoted by large floral displays, floral mechanisms that increase pollen carryover may have selective value.