bluuebunny/crossref_metadata_2025 huggingface dataset:
DIOECY IN BAUHINIA RESULTING FROM ORGAN SUPPRESSION
Authors: Tucker Shirley C.
Published: January 2018

Bauhinia malabarica and B. divaricata have both been reported to have dimorphic flowers; floral development of these species has been investigated and compared using SEM. B. malabarica is subdioecious, with three types of flowers: perfect, staminate, and carpellate. Individual trees usually have only one type of flower. Perfect and carpellate flowers have similar initiation of floral organs; each has five sepals, five petals, two whorls of five stamen primordia and a carpel primordium. The carpels of carpellate flowers do not differ from those of perfect flowers throughout development. Both have a gynophore or stipe and a cuplike hypanthium. Stamen development diverges markedly after mid‐development: the perfect flowers have ten stamens in two whorls, the outer with longer filaments than the inner. All stamens have anthers, which are covered abaxially with abundant inflated trichomes. Carpellate flowers have a circle of short cylindrical staminodia, each bearing a few hairs, about the base of the carpel on the rim of the hypanthium. Heteromorphy in B. malabarica is effected by suppression of stamen development, even though the usual number of stamen primordia is initiated. Suppression of stamens occurs at midstage in development in carpellate flowers of B. malabarica, and is complete. In B. divaricata nine stamen primordia are released from suppression in late stage, undergo intercalary growth and form a staminodial tube around the carpel stipe. The dimorphy in B. divaricata is expressed late in bud enlargement as divergent rates of growth in the carpel in the two morphs.
FLAVONOID DIVERSIFICATION IN THE ACHILLEA AGERATIFOLIA AND A. CLAVENNAE GROUPS (ASTERACEAE)
Authors: Franzén R.
Published: January 2018

The Achillea ageratifolia and A. clavennae groups (Asteraceae, tribe Anthemideae) were investigated for intra‐ and interspecific leaf flavonoid variation. Numerous flavonoid glycosides, mostly unidentified, and variously methylated free aglycones based on scutellarein, 6‐hydroxyluteolin, quercetagetin, and 6‐hydroxy‐kaempferol were detected. The distribution of methylated aglycones among individuals of A. ageratifolia was used to model the putative biosynthetic pathways. Several steps in the biosynthesis probably involve enzymes (methyltransferases) with strict positional specificities and broader substrate specificities. Geographical patterns in the flavonoid content of A. ageratifolia were only partly consistent with the current concept of A. ageratifolia. Different flavonoid profiles in A. ageratifolia do not appear to be of crucial importance in its adaptation to different habitats. The species of the A. clavennae group were clearly separable on flavonoid profiles and the presence of a hybrid population was supported by the flavonoid data. Interspecific differences in number of glycosides in relation to the number of free aglycones are discussed.
SECONDARY PHLOEM ANATOMY IN CORDAITEAN AXES
Authors: Taylor Edith L.
Published: January 2018

Secondary phloem anatomy in cordaitean axes is described based on Carboniferous coal ball permineralizations from Kansas and Ohio. In both stems and roots, phloem consists of alternating, tangential bands of sieve cells and axial parenchyma. Sieve cells are elongate with tapered end walls and have oval‐rectangular sieve areas on their radial walls. A narrow band of tissue close to the cambium is interpreted as phloem that was probably functional at the time of deposition; the remainder of the extensive secondary phloem presumably represents nonconducting tissue and can be divided into a number of zones based on histological characters. The changes that occur from the innermost phloem out to the periphery of the stem are discussed and are compared with previous descriptions of cordaite phloem.
ELECTROPHORETIC EVIDENCE FOR GENETIC DIPLOIDY IN PSILOTUM NUDUM
Authors: Soltis Pamela S. , Soltis Douglas E.
Published: January 2018

Psilotum nudum (2n = 104) has been considered an ancient polyploid, having resulted from repeated cycles of hybridization and allopolyploidy. However, electrophoretic analysis indicates that this species is genetically diploid despite its high chromosome number. Sixteen enzymes, encoded by 28 loci, revealed in P. nudum the number of isozymes typical of diploid seed plants. There is, therefore, no evidence of polyploid gene expression for the enzymes analyzed. These results for Psilotophyta are similar to those obtained for other lineages of homosporous pteridophytes, i.e., Arthrophyta and homosporous Microphyllophyta and Pteridophyta, all of which should be considered genetically diploid. Several hypotheses have been proposed to explain these results, most notably 1) cycles of allopolyploidy followed by massive gene silencing, and 2) initiation of these lineages with high chromosome numbers, possibly via chromosomal fission. Discrimination between these hypotheses awaits testing with molecular genetic techniques.
COMPETENCY FOR GRAVIRESPONSE IN THE LEAF‐SHEATH PULVINUS OF AVENA SATIVA: ONSET TO LOSS
Authors: Brock Thomas G. , Kaufman Peter B.
Published: January 2018

The development of the leaf‐sheath pulvinus of oat (Avena sativa L. cv. Victory) was studied in terms of its competency to respond to gravistimulation. Stages of onset of competency, maximum competency and loss of competency were identified, using the length of the super‐tending internode as a developmental marker. During the early phases in the onset of competency, the latency period between stimulus and graviresponse decreased and the steady state response rate increased significantly. When fully competent, the latency period remained constant as the plant continued to develop, suggesting that the latency period is relatively insensitive to quantitative changes (e.g., in carbohydrate or nutrient availability) at the cell level within the plant. In contrast, the response rate was found to increase with plant development, indicating that graviresponse rate is more strongly influenced by quantitative cellular changes. The total possible graviresponse of a single oat pulvinus was confirmed to be significantly less than the original presentation angle. This was shown to not result from a loss of competency, since the graviresponse could be reinitiated by increasing the presentation angle. As a result of the low overall graviresponse of individual pulvini, two or more pulvini are required to bring the plant apex to the vertical. This was determined to occur through the sequential, rather than simultaneous, action of successive pulvini, since a given pulvinus lost competency to gravirespond shortly after the next pulvinus became fully competent.
ALLOZYME VARIATION WITHIN AND AMONG MATURE POPULATIONS OF SPECKLED ALDER (ALNUS RUGOSA) AND RELATIONSHIPS WITH GREEN ALDER (A. CRISPA)
Authors: Bousquet Jean , Cheliak William M. , Lalonde Maurice
Published: January 2018

Vegetative tissues from 14 sexually mature populations of speckled alder (Alnus rugosa (Du Roi) Sprengel) in Québec have been analyzed for electrophoretically demonstrable variation in 9 enzymes encoding a total of 15 loci. Speckled alder demonstrated a diploid‐like expression for all polymorphic loci investigated. Populations were in Hardy‐Weinberg equilibrium for the 9 polymorphic loci observed. The total expected heterozygosity was 0.173. Analysis of fixation indices indicated a slight deficiency of heterozygotes, relative to panmictic expectations. This was likely due to weak population differentiation, which did not follow any particular geographical trend. Qualitative estimates of interpopulation rates of gene flow were high, and in good agreement with the small pair‐wise population genetic distances and among‐population fixation index. Levels of genetic diversity and partition of this diversity were similar to previous observations obtained with the sympatric species A. crispa (Ait.) Pursh. However, no phenomena of interspecific hybridization were noted. The average genetic distance between these two alder species was large, with a value of 0.4, emphasizing the different ecological niches colonized by each of the two species. The estimate of divergence time between these two taxa was two million years. It is in agreement with the hypothesis of repetitive spatial isolation of each species in ice‐free refugia during the Pleistocene, thus promoting their reproductive isolation. The interspecific divergence noted at the enzyme level allowed for the easy electrophoretic identification of each taxon.
COMPARATIVE ANATOMY AND SYSTEMATICS OF WOODY SAXIFRAGACEAE: TETRACARPAEA
Authors: Hils Matthew H. , Dickison William C. , Lucansky Terry W. , Stern William Louis
Published: January 2018

Vegetative and reproductive anatomy and morphology are described for the first time for Tetracarpaea tasmannica Hook., a small shrub endemic to Tasmania. Tetracarpaea, a monotypic genus, has many characteristics of other woody Saxifragaceae, such as wood with solitary pores, scalariform perforation plates, sparse axial xylem parenchyma, tracheids, spiral thickenings in tracheary elements, and perforated ray cells. The tracheary elements of Tetracarpaea are much smaller than those characteristic of the Escallonioideae, a feature probably related to its montane forest habitat. Other features of Tetracarpaea inconsistent with most Escallonioideae include dark‐staining deposits in the ray cells; a unilacunar, one‐trace nodal pattern; lack of unicellular foliar trichomes; simple craspedodromous venation; areole development that is lacking or incomplete; straight and tapered veinlets; abaxial fibers associated with the foliar vascular bundles; and lack of bundle sheaths. The genus is further characterized by complete, hypogynous, tetramerous flowers. The essentially apocarpous gynoecium has multiovulate carpels, each supplied by three veins that reach the stigma. Ovules are anatropous, bitegmic, and crassinucellate. Lateral sepal bundles are derived either from the sepal midrib or from the petal‐plane bundles; stamens are supplied by independent traces or by bundles originating from compound traces in both sepal‐ and petal‐planes. The follicular fruits possess a sclerenchymatous endocarp and contain winged seeds that have a membranous testa, a ridged surface, and a cellular endosperm. Reproductive morphological and anatomical features are more consistent with features of the Saxifragoideae than with the Escallonioideae or the Cunoniaceae, although the essentially apocarpous gynoecium with multiovulate carpels is not found in these groups. Vegetative and reproductive characteristics indicate that Tetracarpaea is more closely related to Saxifragaceae than to Cunoniaceae. It is possible this isolated genus should have separate familial status.
ONTOGENY OF THE COTYLEDONARY REGION OF CHAMAESYCE MACULATA (EUPHORBIACEAE)
Authors: Hayden W. John
Published: January 2018

Development of the cotyledonary region in Chamaesyce maculata is described from germination of the seed through formation of the dense mat of branches which characterize this common weed. The cotyledonary node is trilacunar with split‐lateral traces. Epicotyl development is limited to a pair of leaves (“V‐leaves”) inserted directly above and decussate to the cotyledons. The two V‐leaves are also vascularized by three traces and insertion of these traces relative to the vasculature at the immediately subjacent cotyledonary node is asymmetrical; four of the six V‐leaf traces arise on one side of the intercotyledonary plane and two arise on the opposite side. Further shoot development is limited to lateral branches that develop sequentially from cotyledonary axillary buds, and then from de novo buds which arise at bases of previously developed lateral branches. The first axillary bud to develop is located on that half of the seedling which supplies the V‐leaves with four traces. Development or insertion of the third and fourth branches (first and second de novo branches) relative to the first and second (cotyledonary) branches occurs in two patterns, termed cis and trans. Subsequent de novo branches generally develop between the two most recently developed branches on that half of the seedling, gradually forming a large branch plexus at the cotyledonary region. In mature robust specimens, however, the sequence of lateral branch development may become irregular. Structure of the cotyledonary region of C. maculata does not readily support widely held concepts of homology between the pleiochasium of Euphorbia subgenus Agaloma and the lateral branch system of Chamaesyce.
ESTIMATES OF INTRAGAMETOPHYTIC SELFING AND INTERPOPULATIONAL GENE FLOW IN HOMOSPOROUS FERNS
Authors: Soltis Pamela S. , Soltis Douglas E. , Holsinger Kent E.
Published: January 2018

Relatively little information is available on mating systems and interpopulational gene flow in species of homosporous pteridophytes. Because of the proximity of antheridia and archegonia on the same thallus, it has long been maintained that intragametophytic selling is the predominant mode of reproduction in natural populations of homosporous ferns and other homosporous plants. Furthermore, quantitative estimates of interpopulational gene flow via spore dispersal are lacking. In this paper, we examine five species of homosporous ferns (Botrychium virginianum, Polystichum munitum, P. imbricans, Blechnum spicant, and Dryopteris expansa) and present estimates of 1) rates of intragametophytic selling, 2) levels of interpopulational gene flow, and 3) interpopulational genetic differentiation (FST). Our data demonstrate that mating systems vary among species of ferns, just as they do among species of seed plants. The data also suggest that levels of interpopulational gene flow are generally high. The FST values indicate little genetic divergence among populations for all species except Dryopteris expansa, which exhibits significant levels of interpopulational genetic differentiation. Patterns of genetic diversity in the five species examined are related to the mating system and rate of interpopulational gene flow in each species. The FST values for all species except Botrychium virginianum are in close agreement with those predicted for an island model of population structure.
DEVELOPMENTAL CHANGES IN CONTENT OF FOLIAR SECRETORY CAVITIES OF TAGETES ERECTA (ASTERACEAE)
Authors: Russin William A. , Uchytil Thomas F. , Feistner Gottfreid , Durbin Richard D.
Published: January 2018

The quantitative and qualitative changes in the contents of foliar secretory cavities during development of Tagetes erecta CV. Moonshot plants were determined. Separation of the secretory components by HPLC yielded three major compounds, subsequently identified by mass spectroscopy, UV spectra, and cochromatography as indole, piperitenone, and piperitone. Comparison of extracts from isolated cavities vs. lamina without cavities showed that in all cases the components were absent from lamina tissues. The quantities of indole and piperitone, in general, increased as the plants developed up to the stage of early flowering, when there was a reduction in total content. At late flowering, the amounts of these components, once again, increased. Concomitantly, the amount of piperitenone decreased during plant development. At all ages studied, indole comprised at least 99% of the total secretion product. This is the first report of the secretory components being restricted to the cavities.
ECOLOGY AND SYSTEMATICS OF HYPOXIS SESSILIS AND H. WRIGHTII (HYPOXIDACEAE) IN SOUTHERN FLORIDA
Authors: Herndon Alan
Published: January 2018

Fire acts as a strong flowering stimulus for Hypoxis sessilis and Hypoxis wrightii in southern Florida. Flowering intensity reaches a peak during the period 6–12 weeks postburn. Thereafter, reproductive activity decreases and follows a seasonal pattern with maximum intensity observed during the summer months. Some plants in each population are reproductively active throughout the year. In addition to increasing reproductive intensity, fire also influences the morphology of the inflorescence. Those inflorescences produced shortly after the burn are larger, more likely to have two flowers, and have chasmogamous flowers. Within three weeks after the start of flowering, all flowers produced by the plants are cleistogamous. Inflorescence size decreases soon afterward. Easy recognition of the two species is hampered by this morphological plasticity, but they retain enough distinguishing characteristics in southern Florida to be considered separate species.
QUANTITATIVE VARIATION IN VULPINIC AND PINASTRIC ACIDS PRODUCED BY TUCKERMANNOPSIS PINASTRI (LICHEN‐FORMING ASCOMYCOTINA, PARMELIACEAE)
Authors: Golojuch S. Thomas , Lawrey James D.
Published: January 2018

Tuckermannopsis pinastri is a lichen species found commonly on rocks and tree branches in boreal and alpine habitats in the northern United States. Members of this species produce three yellow‐pigmented phenolic compounds: usnic, pinastric, and vulpinic acids. The objective of our study was to quantify the variation in concentration of the latter two of these compounds in relation to substrate factors, chlorophyll content, and thallus size. Using high‐performance liquid chromatography, we analyzed 120 thalli of T. pinastri collected randomly from a single large population located at Spruce Knob, West Virginia. Although individuals were sampled from both tree and rock substrates that differed markedly in light intensity, these environmental factors were not correlated with observed variations in vulpinic or pinastric acid concentrations. Instead, compound concentrations were correlated most closely with thallus size, with small rather than large thalli having the highest concentrations of the two compounds. Small thalli did not have higher concentrations of chlorophylls than large thalli, however, which suggests that the rate of production of secondary compounds by the fungus in T. pinastri is independent of algal biomass. Inasmuch as lichen secondary compounds serve a defensive role against microorganisms and herbivores, our results suggest that small, juvenile thalli are better defended than more mature thalli.
EFFECTS OF A WINTER FIRE ON SARRACENIA ALATA AND S. PSITTACINA
Authors: Barker Nancy G. , Williamson G. Bruce
Published: January 2018

The effects of a prescribed winter burn on two species of pitcher plant, Sarracenia alata and S. psittacina, were investigated by comparing changes in variables measured before and after the fire in randomly selected plots in a Louisiana savanna. Burned plots showed an increase in foliage and unburned plots showed a decrease in foliage, as measured in total number of leaves (>25 cm) for S. alata and in total cover for S. psittacina. For S. alata, the gain in foliage in the burned plots was less than the loss in foliage in the unburned plots, but for S. psittacina the gain in burned plots was greater than the loss in unburned plots. Seedling recruitment of S. alata after the fire was exponentially related to the number of floral scapes produced in the year before the fire and was greater in burned plots than in unburned plots. Number of floral scapes of both pitcher plant species decreased in the year after the fire, but the decrease occurred equally in burned and unburned plots.
ANATOMICAL DISTINCTIONS BETWEEN THE PISTILLATE SPIKELETS OF THE SPECIES OF WILD‐RICE (ZIZANIA, POACEAE)
Authors: Duvall Melvin R. , Biesboer David D.
Published: January 2018

The most reliable macromorphological characters that can be used to discriminate between the annual species of the genusZizaniaare found in the pistillate spikelet. One aspect of this morphology is a textural dimorphism. The pistillate lemmas and paleas ofZ. aquaticaare chartaceous (papery) whereas those ofZ. palustrisare coriaceous (leathery). Pistillate lemmas and paleas of the two perennial species,Z. texanaandZ. latifolia, are also chartaceous. To determine the anatomical basis for the nature of this character, pistillate lemmas and paleas were either fixed, treated with hydrofluoric acid, and sectioned; or fresh material was sectioned on a freezing microtome. Those with a chartaceous texture were found to have a single layer of thin‐walled, subepidermal fibers whereas those with a coriaceous texture had at least two layers of thick‐walled, subepidermal fibers.
ESTIMATED RATES OF INTRAGAMETOPHYTIC SELFING IN LYCOPODS
Authors: Soltis Pamela S. , Soltis Douglas E.
Published: January 2018

Homosporous pteridophytes are characterized by the production of free‐living, potentially bisexual gametophytes. Because of the close proximity of archegonia and antheridia on the same thallus, it has been assumed that high rates of intragametophytic self‐fertilization would predominate in natural populations of homosporous pteridophytes. Using enzyme electrophoresis we determined sporophytic genotype frequencies for natural populations of three lycopod species, Lycopodium clavatum, L. annotinum, and Huperzia miyoshiana. Based on these genotype frequencies and the estimation procedures of Holsinger (1987), the estimated rates of intragametophytic selfing in these species are extremely low. Estimated selfing rates were greater than 0.000 in only two of 13 populations of L. clavatum, one of six populations of L. annotinum, and one of four populations of H. miyoshiana. Despite the potential for intragametophytic self‐fertilization, the gametophytes of these three lycopod species predominantly cross‐fertilize, although the mechanism(s) promoting intergametophytic matings are unknown. These results are similar to those obtained for homosporous ferns and Equisetum arvense. It is therefore clear that most homosporous pteridophyte species investigated do not exhibit high rates of intragametophytic self‐fertilization; in contrast, intergametophytic matings predominate.
HETERODICHOGAMY IN GRAYIA BRANDEGEI (CHENOPODIACEAE): REPORT FROM A NEW FAMILY
Authors: Pendleton Rosemary L. , McArthur E. Durant , Freeman D. Carl , Blauer A. Clyde
Published: January 2018

The reproductive biology of Grayia brandegei was examined. Although monoecious, Grayia brandegei exhibits a phenotypic dimorphism of protogynous and protandrous mating types known as heterodichogamy. For individual plants, the temporal separation of staminate and pistillate flowering phases appears to be complete. No self‐fertilization is possible in protandrous plants, but may be possible in protogynous plants provided pistillate flowers remain unfertilized. Flowering phases of protogynous and protandrous mating types are synchronized and reciprocal, ensuring cross‐fertilization between mating types. Less than 15% overlap of sexual functions occurred between plants of the same mating type. Protogynous and protandrous plants were randomly dispersed in the environment and in relation to each other. Mating type frequencies did not differ significantly from 1:1. We discuss the possibility of a heterodichogamous pathway to dioecy.
QUANTITATIVE ULTRASTRUCTURE AND PROTEIN COMPOSITION OF DATE PALM (PHOENIX DACTYLIFERA) SEEDS: A COMPARATIVE STUDY OF ENDOSPERM VS. EMBRYO
Authors: Sekhar K. N. Chandra , DeMason Darleen A.
Published: January 2018

Comparative studies on the ultrastructure and protein composition of the embryo and endosperm of date palm (Phoenix dactylifera L.) were conducted. Cells of the embryo cotyledon and endosperm function in reserve storage and contained cell walls, nuclei, and cytoplasm rich in lipid and protein bodies. Morphometric analysis from light and electron micrographs showed that the cell walls of the endosperm occupied 65% of the total cell volume, but only 6% in the embryo. The protein bodies of the endosperm accounted for 11%, whereas those of the embryo occupied more than half of the total cell volume. The volume of organelles and organelle‐free cytoplasm in the endosperm was negligible, suggesting that most of the extractable endosperm proteins are localized in the protein bodies. Extractable proteins in the embryo may come from cytoplasm, protein bodies, and other organelles. The endosperm contains relatively lower amounts of proteins than does the embryo. Proteins extracted from both tissues were compared using SDS‐polyacrylamide gel electrophoresis, tube gel isoelectric focusing, and two‐dimensional electrophoresis. Proteins of both the tissues were heterogeneous in molecular mass and charge. The majority of the proteins were similar in molecular mass and charge in the two tissues, suggesting that most of the storage proteins are probably the same. However, there were also several embryo‐ and endosperm‐specific proteins apparent in both the first‐ and second‐dimension gels. The endosperm‐specific proteins may play an important role in germination and seedling development.
A COMPARISON OF ENDOSPERM AND EMBRYO PROTEINS OF THE PALM WASHINGTONIA FILIFERA
Authors: Sekhar K. N. Chandra , DeMason Darleen A.
Published: January 2018

Comparative studies on the protein composition of the endosperm and embryo of Washingtonia filifera (Lindl.) Wendl. were conducted. On a fresh weight basis, the endosperm contained lower amounts of protein than did the embryo. This correlated well with lower volumes of protein bodies and cytoplasm in the endosperm than in the embryo. Endosperm proteins were derived mainly from the protein bodies because the volume of organelle‐free cytoplasm was negligible, whereas the source of the proteins in the embryo may be the protein bodies, organelles, and the organelle‐free cytoplasm. Proteins of the two tissues were compared using SDS‐polyacrylamide, isoelectric focusing and two‐dimensional gel electrophoresis. In the first‐dimension analysis, proteins of the two tissues were heterogeneous in molecular mass and charge. In the first‐ and second‐dimension gels, the majority of the protein bands were similar in the two tissues, but a few bands were specific to each tissue type. The similarities in the proteins suggest that the storage proteins are probably the same in the two tissues. The embryo‐specific proteins are probably derived from cytoplasm and organelles.
BRANCHING PATTERN IN ONION ADVENTITIOUS ROOTS
Authors: Pulgarin Antonio , Navascués Julio , Casero Pedro J. , Lloret Pedro G.
Published: January 2018

The pattern of topographic distribution of lateral roots (LRs) along the adventitious root of Allium cepa L. was studied in relation to the adventitious root vascular system. In the onion LRs arise in vertical files opposite the protoxylem poles, thus forming protoxylem‐based ranks of LRs along the mother root. Two protoxylem‐based ranks are shown to support large numbers of LRs, whereas the remaining ranks are considerably less prolific. Within each rank short distances between longitudinal neighbor LRs are uncommon. The results suggest that the developing LR influences the location of subsequent LRs forming in the same protoxylem‐based rank. The frequency with which longitudinal neighbor LRs formed in adjacent protoxylem‐based ranks was significantly high, whereas their appearance in the same rank or in nonadjacent ranks was more restricted. Similarly, the existence of nonrandom clumps of LRs could be demonstrated at certain levels of the adventitious root. The possible effects of interaction between protoxylem‐based ranks of LRs as well as likely agents operating from the parent root vascular system are discussed insofar as they represent factors favoring the clumping of LRs.
EQUATIONS FOR THE MOTION OF AIRBORNE POLLEN GRAINS NEAR THE OVULATE ORGANS OF WIND‐POLLINATED PLANTS
Authors: Niklas Karl J.
Published: January 2018

A technique is presented that is capable of predicting the motion of airborne pollen grains and the probability of pollen capture by wind‐pollinated plants. Equations for the motion of rigid‐walled particles (= pollen grains, spores, or Sephadex beads) in a supporting, compressible fluid (= air) are derived from the first principles of fluid dynamics. These equations are incorporated into a computer program (MODEL) which can be used with a desktop computer. The operation of MODEL requires empirical data on the pattern of airflow or the motion of a pollen species around the surfaces of the taxonomically relevant ovulate plant organ. With this information, MODEL can predict the behavior of any pollen species for which physical properties (size and density) are specified or empirically known. The significance of this procedure lies in the quantification of physical phenomena that influence the mechanics and fluid dynamics of pollen capture in wind pollination. The technique is illustrated and tested by its application to two grass species (Setaria geniculata and Agrostis hiemalis) for which velocity fields of pollen motion have been previously reported.
SIZE VARIABILITY AND SELF‐THINNING IN WILD‐RICE (ZIZANIA AQUATICA)
Authors: Weiner Jacob , Whigham Dennis F.
Published: January 2018

Size variability decreases during the course of density‐dependent mortality (self‐thinning) in dense, naturally‐occurring monocultures of wild‐rice in a tributary to the Chesapeake Bay. As self‐thinning progresses, the size distribution changes from high inequality and positive skewness to become more uniform and equal. This is consistent with the hypothesis that self‐thinning is driven by competition for light.
LIRIODENDRON (MAGNOLIACEAE) FROM THE MIOCENE CLARKIA FLORA OF IDAHO
Authors: Baghai Nina L.
Published: January 2018

Miocene Liriodendron carpels, whole fruiting structures and leaves from Clarkia and Oviatt Creek sites in northern Idaho are preserved as imprints and compressed fossils in soft lacustrine clays. The isolated carpels are indistinguishable from those described as L. hesperia Berry from the Spokane Latah flora. Fruit aggregates from the type Clarkia and Oviatt Creek localities and leaves from three Clarkia sites are considered to be within the range of variation of the single species L. hesperia. Comparisons were made regarding leaf architecture, lower leaf epidermal structures, leaf flavonoid and steroid analysis, morphological features of receptacles and carpels, and the venation pattern of carpels of the fossil material to the two extant species, L. tulipifera L. (native to southeastern United States) and L. chinense Sarg. (native to southeastern Asia). Leaf architecture features analyzed by standard statistical and canonical tests and marginal venation patterns near the base of leaves suggest that L. hesperia is more similar to L. tulipifera, whereas the size dimensions of lower epidermal cells and the common presence of two sterane compounds imply that L. hesperia is more similar to L. chinense. The fossil species, however, is a distinct taxon indicated by statistical discriminant and canonical tests, leaf base shape, often smaller epidermal cell dimensions, and the shape of round receptacle carpel scars. Both the fossil and the two living Liriodendron species are associated with comparable mixed mesophytic floras.
GERMINATION AND SEEDLING EMERGENCE IN SPERGULA ARVENSIS
Authors: Wagner Lisa K.
Published: January 2018

Spergula arvensis L. (Caryophyllaceae) is a cosmopolitan weedy annual that exhibits a genetically based seed coat polymorphism in which two primary seed types, papillate (P) and nonpapillate (NP), are produced. This study examined germination response of the two morphs and seedling emergence in Pacific coast populations. Germination behavior was complex and variable among populations and between seed morphs. Seeds from some populations exhibited greater temperature sensitivity and/or differentiation between morphs. Freshly produced seeds from grassland and ruderal populations were strongly dormant at the time of dispersal, in contrast to seeds from cultivated or summer‐wet populations. In San Francisco Bay area populations, germination and seedling emergence was largely simultaneous, following the first substantial fall rains.
EXPERIMENTAL HYBRIDIZATION, CHROMOSOMAL DIVERSITY, AND PHYLOGENY WITHIN GAURA (ONAGRACEAE)
Authors: Carr Bruce L. , Gregory David P. , Raven Peter H. , Tai William
Published: January 2018

Patterns of interfertility for intersectional hybridizations in Gaura are generally consistent with current taxonomic hypotheses regarding the sectional division of the genus. Crossability is generally lower for intersectional crosses than for intrasectional, interspecific crosses. Average intersectional cross‐success ranged from 0–14% among the eight sections, and a total of 54 intersectional hybrids were produced from 1,872 intersectional pollinations. Low rates of capsule‐set and no intersectional hybrids were produced by G. mutabilis (section Gauridium), an early offshoot of a primitive ancestor of Gaura. Two species of section Xerogaura that are regarded as relicts of the primitive ancestor of all other Gaura showed low averages for cross‐success, but did produce hybrids in combination with three relatively advanced sections (Campogaura, Stipogaura, Pterogaura). Low capsule‐set and no intersectional hybrids were produced by G. parviflora (section Schizocarya). Extreme morphological specialization for autogamous reproduction has been accompanied by reproductive isolation of G. parviflora. Only three hybrids resulted from crosses using G. coccinea (section Campogaura), a polyploid complex. Each successful cross paired G. coccinea with a putative progenitor, either a species of section Xerogaura or G. villosa of section Stipogaura. Hybrids of G. coccinea with odd ploidy number showed reduced pollen staining. Species of Stipogaura produced only three hybrids, one each in combination with species of sections Xerogaura, Campogaura, and Pterogaura. Gaura drummondii (section Xenogaura) registered the highest average cross‐success despite being a tetraploid. All 25 hybrids of G. drummondii resulted from crosses with G. suffulta, and were triploids that showed reduced pollen staining. Intersectional crosses fail to support the hypothesized relationships of G. drummondii either to G. coccinea or to species of section Stipogaura. Section Gaura produced moderate averages of cross‐success, but all 20 hybrids resulted from crosses with G. suffulta. Fifty of the 54 intersectional hybrids were descended from a species of section Pterogaura. Crosses that used G. suffulta as one parent produced 49 of these hybrids. Four hybrids were from crosses with G. macrocarpa (section Xerogaura), and the remaining 45 were due to the recurrent success of crosses that paired G. suffulta as maternal parent with either G. drummondii or a species of section Gaura.
A QUALITATIVE MODEL FOR EVALUATING THE EFFECTS OF FLOWER ATTRACTIVENESS ON MALE AND FEMALE FITNESS IN PLANTS
Authors: Stanton Maureen L. , Preston Robert E.
Published: January 2018

Theories of sex allocation make a number of predictions about the relationship between male and female resource investment in flowering plants and realized fitness. Testing these predictions requires quantitative information on costs and benefits associated with various allocation patterns. These data are difficult to obtain even in experimental settings, and may be impossible to obtain in many natural populations. Experimental studies of pollination and female reproduction in plants have been facilitated by the qualitative distinction between resource and pollen limitation of seed set. Here, we present an analogous model for studying relationships between pollinator visitation, pollen production, and pollen export. For animal‐pollinated species where seed production is resource‐limited, maternal fitness may be enhanced by conserving resources rather than investing in secondary attractive structures. In contrast, pollen export is likely to increase with increasing allocation to advertisements and rewards, at least until anthers are stripped of pollen.
APHANOSPERMA, A NEW GENUS OF ACANTHACEAE FROM MEXICO WITH UNUSUAL DIASPORES
Authors: Daniel Thomas F.
Published: January 2018

Recent collections and studies of an unusual species of Acanthaceae from the dry forests of northwestern Mexico reveal it to be generically distinct. Aphanosperma comprises a single species, A. sinaloensis, and is included in the Ruellioideae: Justicieae: Odontoneminae near Carlowrightia. At least four characteristics of the capsule appear to be unique in the family, including progressive reflexing during maturation and permanent retention of the seeds in the capsule valves which thus become the diaspores. The species is shown to be self‐compatible and fully autogamous.
A QUANTITATIVE CYTOGENETIC ANALYSIS OF AN INTERSECTIONAL HYBRID IN HELIANTHUS (COMPOSITAE)
Authors: Jackson R. C.
Published: January 2018

From numerous pollinations of Helianthus laciniatus A. Gray sect. Ciliares by H. annuus L. sect. Helianthus (each with n = 17), a single hybrid was grown to maturity. The hybrid was vigorous but only 2.24% pollen‐fertile compared to greater than 96% fertility in the parents. Backcrossing to the parental species was unsuccessful, so the possibility of gene flow between the species in nature is remote. Chromosome pairing in the parental plants was normal, but the hybrid was heterozygous for at least one paracentric inversion and numerous translocations. Chiasma frequencies of the parental genotypes were significantly different. The hybrid was significantly different from H. laciniatus and from the midparent value but not from H. annuus. These differences in chiasma frequencies were tested by the way chiasmata were allocated among the different meiotic configurations. Methods of converting multivalents to bivalent equivalents for comparison of chiasmata distribution among species and hybrids are demonstrated.
LEAF ANATOMY IN SANSEVIERIA (AGAVACEAE)
Authors: Koller Alan L. , Rost Thomas L.
Published: January 2018

Forty‐nine taxa of Sansevieria were examined to provide the first detailed description of leaf anatomy in the genus, as well as to determine the cellular organization of the water‐storage tissue present in the central mesophyll of all leaves. Leaf form ranges from flat through cylindrical, with varying degrees of xeromorphic characteristics, including cuticle thickness, stomatal depth, fiber content, and fiber cell development. Mesophyll in all species is divided into an outer region of chlorenchyma and a central region of colorless water‐storage tissue. The water‐storage tissue comprises a highly branched 3‐dimensional network of living cells, among which are many dead, thin‐walled water‐storage cells. Species with more extreme xeromorphic characteristics tend to have a greater percentage of their water‐storage tissue composed of water‐storage cells. In 28 taxa, water‐storage cells have spiral or reticulate wall bands. These taxa tend to be more xeromorphic. The wall bands may serve an important structural role in drought tolerance.
CHANGES IN LEAF CHARACTERISTICS OF SPECIES ALONG ELEVATIONAL GRADIENTS IN THE WASATCH FRONT, UTAH
Authors: Ehleringer James R.
Published: January 2018

Leaf absorptances and leaf angles were measured on 159 of the most common vascular plant species along a precipitation/elevation transect in the Wasatch Mountains. At the community level, leaf angles were steepest in the driest saltbush community sites, became progressively more horizontal in wetter communities, and reached a minimum in the midelevation mountain brush communities. At higher elevation plant communities, where growth is delayed until summer months because of heavy snowfall, leaf angles were again steeper. Leaf absorptances among all life forms were uniformly high along the entire transect until the driest saltbush communities where a number of species exhibited reduced leaf absorptances. The results are discussed within the context of mechanisms for reducing solar radiation absorption along an aridity transect.
GROWTH IN MEDEOLA VIRGINIANA CLONES. II. STOCHASTIC SIMULATION OF VEGETATIVE SPREAD
Authors: Cain Michael L. , Cook Robert E.
Published: January 2018

Medeola virginiana, a forest understory herb, has been hypothesized to minimize competition among ramets by positioning ramets regularly in space (Bell, 1974). We have constructed a computer model that simulates vegetative spread in Medeola by incorporating the variation in growth form found in natural populations. This stochastic model, based on data in Cook (1988), includes variation in the number and type of daughter ramets, the distance between parent and daughter ramets, and the angle of divergence between the lines of growth of the parent and daughter rhizomes. Over a wide range of initial ramet densities, initial degrees of ramet dispersion, and intensities of ramet mortality, our simulations indicate that the growth pattern of M. virginiana leads to aggregated distributions of ramets with overlapping leaf canopies. The observed aggregation of ramets may result from the tendency for directional but variable growth in clones. Such variable growth calls into question adaptive interpretations based on deterministic models that utilize the mean values of growth parameters but ignore the highly variable nature of clonal growth.
MYCORRHIZAE AND MYCORRHIZAL FUNGI OF CALYPSO BULBOSA
Authors: Currah R. S. , Hambleton S. , Smreciu A.
Published: January 2018

The seasonal development and fungal endophytes of the mycorrhizal roots ofCalypso bulbosa(L.) Oakes were studied using fresh collections from Alberta and herbarium specimens from six herbaria. Typically, a single pair of mycorrhizal roots are produced at the base of a single corm each growing season. No evidence was found to support the putative existence of a coralloid rhizome in this species. The pattern of fungal infection, peloton formation, and breakdown is similar to other nonsaprophytic, terrestrial orchids. The endophytic fungi of a single mycorrhizal root can belong to a number of different fungal taxa. Fungi isolated and described includeRhizoctonia anaticulaCurrah,Thanatephorus pennatusCurrah,Leptodontidium orchidicolaSigler and Currah,Phialocephala fortiniiWang and Wilcox, and two unnamed isolates ofRhizoctonia.
FERTILIZATION IN PLUMBAGELLA MICRANTHA
Authors: Russell Scott D. , Cass David D.
Published: January 2018

The megagametophyte of Plumbagella micrantha, consisting of three cells: an egg, a central cell, and a single antipodal, represents the most structurally reduced female gametophyte of the flowering plants. In the absence of synergids, the pollen tube enters the megagametophyte through a filiform apparatus at the base of the egg, continues growth for 40 μm through the egg‐central cell wall, until reaching a region of strong curvature near the chalazal end of the egg. A terminal pollen tube aperture then forms, the sperm cells and vegetative nucleus are released between the egg and central cell, and the sperm undergo gametic fusion, thereby effecting double fertilization. The mode of fertilization in Plumbagella is therefore similar to that of Plumbago that has been described elsewhere.
A MORPHOLOGICAL STUDY OF ALVIMIA (POACEAE: BAMBUSEAE), A NEW BRAZILIAN BAMBOO GENUS WITH FLESHY FRUITS
Authors: Soderstrom Thomas R. , Londoño Ximena
Published: January 2018

Alvimia is a new genus of climbing bamboo that occurs in a relatively small area of restinga of coastal Bahia, Brazil. It is easily distinguished from other genera of the New World by a combination of several features: fleshy fruits, flowers with two stamens arranged in pseudospikelets, and the climbing habit. The Brazilian Alvimia, Mexican Olmeca, and one Peruvian species of Guadua are the only bamboos from America with fleshy fruits, a feature also found in a few Asiatic bamboos such as Dinochloa, Melocalamus, Melocanna, and Ochlandra. Three new species in Alvimia are described: A. auriculata, A. gracilis, and A. lancifolia.
MAINTENANCE OF GYNODIOECY IN SILENE ACAULIS (CARYOPHYLLACEAE): STAGE‐SPECIFIC FECUNDITY AND VIABILITY SELECTION
Authors: Shykoff Jacqui A.
Published: January 2018

Through a combination of field and greenhouse experiments, I examined the factors contributing to the maintenance of female individuals in natural populations of the gynodioecious alpine plant Silene acaulis (Caryophyllaceae). Hand‐pollinated female plants produced 3.8 times as many seeds as did either self‐ or outcross‐pollinated hermaphrodites, and open‐pollinated females produced 2.9 times as many seeds as open‐pollinated hermaphrodites. Females and hermaphrodites produce seeds of similar mass, and the same number of seeds per fruit, but females set fruit from a higher proportion of their flowers. This fecundity difference alone is sufficient to sustain equilibrium frequencies of females in natural populations. Greenhouse germination trials revealed no difference in the timing or probability of germination among seeds produced from females, selfed, and outcrossed hermaphrodites. Seedlings produced by females had the highest juvenile survivorship followed by those from outcrossed hermaphrodites and then those from selfed hermaphrodites. Differences between selfed hermaphrodites and the other treatments provide evidence for inbreeding depression at the establishment stage. The discrepancy between success of seedlings from female plants and those from outcrossed hermaphrodites suggests either that superior resources are allocated to seeds by females (maternal effect) or that seedlings of females are genetically superior to those of hermaphrodites.
SOME MORPHOLOGICAL FEATURES FOR GENERIC CHARACTERIZATION AMONG THE CASUARINACEAE
Authors: Torrey John G. , Berg R. Howard
Published: January 2018

The family Casuarinaceae has been divided recently into four genera on the basis of differences in chromosome numbers, morphological characters including stem morphology, structures of the male and female flowers and fruits, their modern biogeography, and fossil record. All members of the family are characterized by highly reduced leaves, photosynthetic deciduous branchlets, and adaptations to xeric or hot humid environments. The genus Gymnostoma is characterized by multiple rows of naked stomata along the central vertical faces of the stem internodes. Casuarina and Allocasuarina develop vertically aligned rows of stomata in deep furrows that alternate with stem ridges. Epidermal hairs, formed within the furrows, occur in different species in conformity with other xeric characters. The characters described in this paper conform to the view that the morphological structures represent reduction and specialization rather than primitiveness.
ROOT SYSTEMS, SPATIAL PATTERNS, AND COMPETITION FOR SOIL MOISTURE BETWEEN TWO DESERT SUBSHRUBS
Authors: Manning Sara J. , Barbour Michael G.
Published: January 2018

Haplopappus cooperi and Chrysothamnus teretifolius are important elements on alluvial fans in the Owens Valley of California. Selective removal field experiments, followed for 7 months, revealed that Haplopappus predawn water potentials were significantly less negative after removal of neighboring plants of either species, whereas Chrysothamnus predawn water potentials were unchanged, compared to controls. Haplopappus also showed a more dramatic response in water potential following supplemental watering at the end of the dry season. Excavations showed that the root systems of the two species were different: the majority of Haplopappus root biomass was within the upper 20 cm of soil, but for Chrysothamnus it was below 40 cm depth. Spatial pattern was not always a reliable predictor of biotic interaction in this desert community: Chrysothamnus individuals were aggregated, Haplopappus individuals were distributed at random, and plants of the two species were randomly associated.