bluuebunny/crossref_metadata_2025 huggingface dataset:
HOMOPLOID RETICULATE EVOLUTION IN HELIANTHUS (ASTERACEAE): EVIDENCE FROM RIBOSOMAL GENES
Authors: Rieseberg Loren H.
Published: January 2018

Phylogenetic relationships among the 21 taxa comprising Helianthus sect. Helianthus and three outgroup species were assessed by restriction site mapping of the 18S‐25S nuclear ribosomal RNA gene family. Wagner parsimony analysis of the 41 restriction site or length mutations observed produced a single 59‐step most parsimonious tree. This tree was then compared to a cytoplasmic‐based plastid phylogeny for this group. Several major discrepancies were observed between the two phylogenies suggesting both recent and ancient introgression. Furthermore, three cases of diploid hybrid speciation are unambiguously documented and a fourth case is suggested. These data are interpreted to suggest that evolution in Heliathus is reticulate rather than exclusively dichotomous and branching.
PLASMODESMATAL FREQUENCY AND OTHER STRUCTURAL ASPECTS OF ASSIMILATE COLLECTION AND PHLOEM LOADING IN LEAVES OF SONCHUS OLERACEUS (ASTERACEAE), A SPECIES WITH MINOR VEIN TRANSFER CELLS
Authors: Fisher David G.
Published: January 2018

Leaves of Sonchus oleraceus (Asteraceae) were examined with the electron microscope to determine plasmodesmatal frequencies and other structural features relating to the collection of photoassimilate and its subsequent loading into minor veins. Few plasmodesmata occur between mesophyll cells, which contain chloroplasts that are sometimes connected to both the plasmalemma and the tonoplast by membranous tubules. The minor veins consist of tracheary elements, sieve‐tube members, vascular parenchyma cells, and companion cells. The latter two cell types are transfer cells, with some of the fingerlike wall ingrowths in companion cells being traversed lengthwise by plasmodesmata. The frequencies of plasmodesmata at the mesophyllbundle sheath boundary and within are higher at some interfaces than at corresponding interfaces in nine other species, including some that previously had been characterized as loading assimilate via the symplast. It is thus premature to designate all species containing transfer cells in their minor veins as loading assimilate only via the apoplast.
PHENOTYPIC PLASTICITY IN SCENEDESMUS COMMUNIS HEGEW. (CHLOROPHYCEAE). II. EXAMPLES OF ALGAL CYCLO‐ AND NONCYCLOMORPHOSIS
Authors: Egan Patrick F. , Trainor Francis R.
Published: January 2018

A new dimension to the well‐known phenotypic plasticity in Scenedesmus is presented. Large colony type Scenedesmus communis Hegew. reproduced in a typical fashion in batch culture in standard media but produced small colonies (SCT) resembling S. komarekii Hegew. and S. subspicatus Chod. at low cell densities in dilute media. Highest frequency of production occurred after cells had been pretreated in a concentrated (inorganic nutrients) medium. Examples of both cyclic and noncyclic behavior in the life history of Scenedesmus are presented. The noncyclic behavior resembles previous reports on induced heritable changes in flax and tobacco due to different treatment applications of fertilizers. An analysis of gross morphological features using scanning electron microscopy showed that isolated strain SCT1 was similar to S. komarekii (strain UTEX 1236) and isolated strain SCT2 was similar to S. subspicatus (strain UTEX 1358). Growth and morphological expression of the induced SCT strains were highly similar to those of the respective UTEX species. The current state of taxonomy and the implications of phenotypic plasticity on taxonomy in Scenedesmus are discussed.
CHROMOSOMAL ANALYSES AND THE ORIGIN OF ALLOPOLYPLOID POLYPODIUM VIRGINIANUM (POLYPODIACEAE)
Authors: Haufler Christopher H. , Zhongren Wang
Published: January 2018

Polypodium virginianum L. has been treated as a morphologically and chromosomally variable species. Recently, however, two species have been named from within the P. virginianum complex. Chromosome counts reported here confirmed that these segregate species, P. appalachianum Haufler and Windham and P. sibiricum Siplivinskij, are diploids with n = 37. It was further hypothesized that hybridization between these diploids initiated the allotetraploid P. virginianum. Naturally occurring, sterile triploid plants obtained from habitats in which the putative allotetraploid was sympatric with its presumed diploid progenitors have been verified isozymically as backcross hybrids. Meiotic chromosomal behavior showed that the triploids contained univalents and bivalents in nearly equal numbers, confirming that tetraploid P. virginianum contained one genome from each diploid. Observation of three to six trivalents in triploid preparations suggested that the diploids are still closely related genetically. This hypothesis was supported by isozymic studies which found a genetic identity of 0.610 between P. appalachianum and P. sibiricum, a value much higher than the average identity for congeneric fern species studied to date (0.33) and higher than any other species pair in the P. vulgare L. complex (average I = 0.307). These chromosomal and isozymic data help to resolve a biosystematic riddle that has interested pteridologists for over 40 years.
PLANT SIZE AND FORM IN THE UNDERSTORY PALM GENUS GEONOMA: ARE SPECIES VARIATIONS ON A THEME?
Authors: Chazdon Robin L.
Published: January 2018

This study addressed the hypothesis that phylogenetic changes in plant size at reproductive maturity may have facilitated adaptive radiation of Geonoma species within rain forest understory habitats. Leaf size, leaf form, plant size, and growth form were compared within and among 23 species of Geonoma from lowland and montane rain forest areas of Costa Rica and Colombia. Leaf size was significantly correlated with crown height in 18 of the 21 species examined, and with stem diameter in 17 of the species. In species characterized by a gradual ontogenetic transition from bifid to dissected leaves, shoots with bifid leaves were significantly smaller than shoots with dissected leaves with respect to rachis length, number of plications, and stem diameter. Among species, stem diameter below the crown explained 74% of the variation in leaf size (rachis length). Crown height and stem diameter were positively correlated among clustered species, but not among solitary species or all species combined. Leaf dissection was correlated with crown height among the 17 species with dissected leaves; species with bifid leaves were significantly smaller than species with dissected leaves with respect to leaf size and stem diameter. Solitary species had larger leaves and larger stem diameters than clustered species at the same crown heights. Morphological patterns among species generally followed within‐species trends. These patterns suggest that Geonoma species are variants on a generic theme:within and among species, leaf size and complexity of form increase with stem diameter and crown height. Solitary and clustered growth forms appear to be morphologically convergent; within each of these architectural groups, the generic theme still applies. Evolutionary changes in leaf size, leaf form, and plant size, however, have clearly involved other factors in addition to variation in plant size.
MORPHOLOGICAL STUDIES IN ZYGOPHYLLACEAE. I. THE FLORAL DEVELOPMENT AND VASCULAR ANATOMY OF NITRARIA RETUSA
Authors: Decraene L. P. Ronse , Smets E. F.
Published: January 2018

The floral development and vascular anatomy of Nitraria retusa were investigated in order to understand its characteristic androecium of 15 stamens and to clarify the systematic position of the genus relative to Zygophyllaceae. Sepals arise in a helical sequence and are relatively small at maturity. Petals are initiated almost simultaneously or in a rapid helical sequence. Five stamen primordia arise opposite the sepals. Next, two other antesepalous primordia are incepted centrifugally to the first primordia on the remaining receptacular surface. The outer stamens tend to be squeezed between the petals and upper stamens and appear to make up an antepetalous whorl of stamens. Three carpels arise from a low ringwall and grow into a hairy trilocular pistil. In each locule a single pendulous ovule is present. Disclike nectarial tissue is initiated in pits between the stamens and petals. Long trichomes develop on its surface. It is concluded that the androecium is linked with a haplostemonous condition because the stamens of each triplet develop on strictly localized sectors. The distinction between stamens arising on complex primordia and the inception of three independent units is explained by the “principle of variable proportions.” The vasculature also tends to confirm that the outer stamen pairs belong to antesepalous triplets.
HAIRY‐SHEATH FRAYED #1‐O: A SYSTEMIC, HETEROCHRONIC MUTANT OF MAIZE THAT SPECIFIES SLOW DEVELOPMENTAL STAGE TRANSITIONS
Authors: Bertrand‐Garcia Ralph , Freeling Michael
Published: January 2018

Hairy sheath frayed‐1 (Hsf1‐O), an ethyl methanesolfonate‐induced dominant mutant in maize, was first described as an excessively hairy plant with pronglike projections of sheath that extended from the margin of the leaf blade. We describe several other phenotypes and show that Hsf1‐O affects virtually every segment of the plant. We have identified genetic backgrounds that suppress some of the Hsf1‐O phenotypes. The morphological descriptions reveal a prolongation of cell differentiation in certain tissues and organs. In general, transformations are from more adult to more juvenile, not older to younger. On the assumption that Hsf1‐O acts with the same developmental logic in both the apical meristem and leaf primordia, the leaf sheath is a juvenile blade, not a young blade. Genetic background effects show that the expressivity of the phenotype is influenced by the plant's time to anthesis. The suppression and temporal shift in Hsf1‐O expression patterns in early flowering lines is due to the inherent accelerated maturation of cells in these lines. In early flowering lines, transformations are suppressed and shifted toward the less mature (younger) tissues, organs, and segments of the plant. We conclude that Hsf1‐O is a heterochronic mutation that prolongs the time to maturity (delays terminal differentiation), and that a primordial cell's developmental maturity rather than the cell's position can dictate that cell's fate. Hsf1‐O disconnects the rate of developmental stage transition from the overall flowering‐time rate.
A SYSTEMATIC STUDY OF ENDOTHECIAL THICKENINGS IN THE ORCHIDACEAE
Authors: Freudenstein John V.
Published: January 2018

Endothecial cell thickenings were examined in anther macerations of representative species from 210 genera of the Orchidaceae. Nearly all species examined possessed the characteristic thickened walls which, in several tested species, gave a positive reaction to phloroglucinol, indicating the presence of lignin. Four basic thickening types were identified; distribution of the types was found to be largely in agreement with previously recognized suprageneric groups. Type I thickenings are tightly packed channels of loops or helices and were found in the “neottioid” genera, the Apostasioideae, and putatively basal genera in the remaining subfamilies. Because of its occurrence in the Apostasioideae, which is believed to be the most basal subfamily, Type I is hypothesized to be the plesiomorphic thickening type for the remainder of the Orchidaceae. Type II thickenings appear as scattered loops and may be a synapomorphy for the Orchidoideae, as they were found in all genera sampled from the subfamily except Disperis. Type III thickenings are circular in appearance and were found in the Cypripedioideae and in some members of the Spiranthoideae and Epidendroideae. Type IV thickenings show little regular arrangement, appearing to be scattered bars, and were observed primarily in the Epidendroideae and also in some Spiranthoideae. Three subtypes were recognized in Type III and Type IV. Some genera, such as Triphora, Goodyera, and Elythranthera, had thickenings that appeared intermediate between the recognized types. In general, terrestrial genera were found to have regularly arranged, well‐developed thickenings, while many epiphytic groups showed congested, irregular, thinner thickenings.
POLLEN TUBE GROWTH AND INBREEDING DEPRESSION IN AMSINCKIA GRANDIFLORA (BORAGINACEAE)
Authors: Weller Stephen G. , Ornduff Robert
Published: January 2018

To discriminate between the roles of differential pollen tube growth and inbreeding depression in causing reduced seed production following self‐pollination of distylous Amsinckia grandiflora (Boraginaceae), callose plug and pollen tube production were compared following cross‐ and self‐pollinations of A. grandiflora. Pin (long‐styled morph) × thrum (short‐styled morph) crosses yielded more pollen tubes than pin × pin crosses or pin self‐pollinations; no difference could be detected for the pin × pin or pin self‐pollination categories. Using thrums as the female parent, no significant differences were detected in any pollination category. These results indicate that reduced seed production following self‐fertilization of A. grandiflora is likely to be the result of inbreeding depression rather than inhibition of self pollen tubes.
EXINE PATTERN FORMATION BY PLASMA MEMBRANE IN BOUGAINVILLEA SPECTABILIS WILLD. (NYCTAGINACEAE)
Authors: Takahashi Masamichi , Skvarla John J.
Published: January 2018

Transmission and scanning electron microscopy of exine development in Bougainvillea spectabilis (Nyctaginaceae) confirmed that the exine pattern is initiated by invagination of the microspore plasma membrane at the early tetrad stage. Invaginated plasma membranes take the form of a reticulate pattern that corresponds to the mature exine tectum. Protectum is the first exine layer to be deposited on the reticulate‐patterned plasma membrane. Subsequently, probacules elongate basally on protruding sites of the plasma membrane under the protectum and in the lumina. These sites retreat as the probacules elongate. After the dissolution of the callose wall, a foot layer forms through the accumulation of lamellated structures. Clearly, the plasma membrane serves a determinative role in the initial pattern formation of exine.
GENETIC VARIATION IN BROMUS TECTORUM (POACEAE): POPULATION DIFFERENTIATION IN ITS NORTH AMERICAN RANGE
Authors: Novak Stephen J. , Mack Richard N. , Soltis Douglas E.
Published: January 2018

Allelic variation in seedlings from 60 North American populations of the alien annual grass Bromus tectorum was determined at 25 loci using starch gel electrophoresis. Populations were collected from four regions; east of the Rocky Mountains, Nevada and California, the Intermountain West, and British Columbia. Compared to other diploid seed plants, genetic variation within these populations of B. tectorum is low: 4.60% of loci are polymorphic per population, with an average of 1.05 alleles per locus and a mean expected heterozygosity of 0.012. Although 2,141 individuals were analyzed, no heterozygous individuals were detected, and consequently, mean observed heterozygosity is 0.000. Extensive deviations from Hardy‐Weinberg expectations were observed at every polymorphic locus due to heterozygote deficiencies. The mean genetic identity (Nei's I) between population pairs was 0.980 and indicates a high level of overall genetic similarity among populations. The among‐population component of the total gene diversity is high (GST = 0.478), indicating substantial genetic differentiation among populations. These results are consistent with previous reports for highly self‐pollinating plants of low genetic variation and substantial genetic differentiation among populations. Despite the lack of genetic variation as measured by enzyme electrophoresis, this weedy grass has become exceedingly abundant in a diverse array of arid environments throughout much of western North America, perhaps due to phenotypic plasticity.
POLLEN‐PISTIL INTERACTIONS IN TRISTYLOUS PONTEDERIA SAGITTATA (PONTEDERIACEAE). I. FLORAL HETEROMORPHISM AND STRUCTURAL FEATURES OF THE POLLEN TUBE PATHWAY
Authors: Scribailo Robin W. , Barrett Spencer C. H.
Published: January 2018

Heteromorphic characters and structural features of the pollen tube pathway are described in tristylous Pontederia sagittata to assess their influence on the pollination process and in mediating self‐incompatibility behavior. Heteromorphic characters that distinguish the floral morphs include style length, stigma depth, stigmatic papillae length, stylar parenchyma cell length, area of the stylar canal, stamen height, anther size, and pollen size. Unlike several distylous species that have been investigated, the exine of pollen in P. sagittata was not strongly differentiated among the pollen types, and no differences in stigma cytochemistry were apparent. Features common to the floral morphs were a wet stigma, a hollow trilobed stylar canal separating into two sterile and one fertile canal, and a single anatropous ovule with a highly elaborated integumentary obturator. The similarity in structural features of the pollen tube pathway of P. sagittata to those found in monocotyledonous taxa with gametophytic self‐incompatibility suggests that phylogenetic constraints may have influenced the evolution of trimorphic incompatibility in the Pontederiaceae.
EFFECTS OF TISSUE VOLUME AND LOCATION ON THE MECHANICAL CONSEQUENCES OF DEHYDRATION OF PETIOLES
Authors: Niklas Karl J.
Published: January 2018

Data are presented on the mechanical consequences of dehydration for the petioles of two monocots and two dicots differing in leaf morphology (pinnate leaves ofChamaedorea erumpens and simple leaves of Spathiphyllum ‘clevelandii‘; pinnate leaves of Acer negundo and simple leaves of A. saccharum). The flexural stiffness EI of petioles decreased over a broad range of tissue water potential (– 10 < ψw <– 50 bars). Within the same range of ψ, the second moment of area I and the elastic modulus E were observed to decrease and increase, respectively. However, the mechanical alterations of Chamaedorea and A. negundo petioles were significantly less than those observed for Spathiphyllum and A. saccharum petioles. The increase in E of Spathiphyllum and A. saccharum petioles attending dehydration was linearly correlated with an increase in the relative volume fraction of tissues with lignified, thick cell walls (“support tissues”). The decrease in I of Spathiphyllum and A. saccharum petioles was linearly correlated with a decrease in the relative volume fraction of tissues with nonlignified, thin cell walls (“ground tissues”). Similar trends were observed for the petioles of C. erumpens and A. negundo but were found not to be statistically significant. Anatomical differences in the relative volume fraction and spatial locations of support tissues in the petioles of these four taxa appear to account for the differences observed in the mechanical consequences of petiole dehydration.
THE ROOT APICAL MERISTEM OF ASPLENIUM BULBIFERUM: STRUCTURE AND DEVELOPMENT
Authors: Gifford Ernest M.
Published: January 2018

The root apical meristem of Asplenium bulbiferum Forst. f. has a prominent four‐sided pyramidal cell with its base in contact with the rootcap. Derivatives (merophytes) that contribute to the main body of the root are produced from the three proximal faces of the apical cell. The rootcap has its origin from the fourth (distal) face of the apical cell. The first division in a proximal merophyte is periclinal to the root surface, separating an outer cell and an inner cell. The outer cell is the origin of the outer part of the cortex and the epidermis; the larger inner cell is the origin of the inner cortex, endodermis, pericycle, and vascular tissue. After the establishment of the basic number of cells in a unilayered merophyte, the cells undergo transverse divisions forming longitudinal files of cells. The mitotic index of the apical cell indicates that it is not a quiescent cell. Also, the first plane of division in a newly formed merophyte dictates that the apical cell is the originator of merophytes.
COMPARISON OF PLANT DNA CONTENTS DETERMINED BY FEULGEN MICROSPECTROPHOTOMETRY AND LASER FLOW CYTOMETRY
Authors: Michaelson Martin J. , Price H. James , Ellison John R. , Johnston J. Spencer
Published: January 2018

An improved procedure is reported for determining DNA amounts of plant nuclei. Nuclei stained with propidium iodide, isolated from chopped plant leaves, were passed through an Ortho Cytofluorograph with a Lexel model 95 argon laser (514 nm) and the fluorescence measured, integrated, and recorded using an Ortho 2140 Data Acquisition computer. All nuclear samples were mixed with nuclei of Sultan barley (2C DNA content = 11.12 pg [picogram]) as an internal standard. DNA contents of ten plant species, ranging from 2C = 1.7 pg to 36.1 pg measured by flow cytometry, correlated strongly (r = 0.99, slope = + 1.00) with DNA contents determined from Feulgen‐stained nuclei of the same species using microspectrophotometry. The flow cytometric procedures were sufficiently sensitive to detect differences in DNA content between inbred lines of corn and their F1 hybrids. Our results obtained with improved procedures, specifically using propidium iodide as a fluorochrome and plant nuclei instead of chicken erythrocytes as an internal standard, demonstrate that laser flow cytometry can be a precise, rapid, and reliable method for determining nuclear DNA content of plants.
GROWTH AND WOOD PROPERTIES OF GMELINA ARBOREA (VERBENACEAE) SEEDLINGS GROWN UNDER FIVE SOIL MOISTURE REGIMES
Authors: Ogbonnaya Chuks I. , Nwalozie Marcellus C. , Nwaigbo Leo C.
Published: January 2018

The effects of different watering regimes on vegetative growth, histological properties of wood, and the derived values relevant to paper and pulp production of Gmelina arborea Roxb. were investigated. Soil moisture stress significantly retarded vegetative growth as analyzed by leaf area ratio, root shoot ratio, net assimilation rate, and relative growth rate. Moisture stress also adversely affected specific gravity of the wood, fiber length, diameter, lumen size, and fiber wall thickness, but enhanced flexibility coefficient, lowered slenderness ratio, and runkel ratio. Although water stress reduces the volume of wood produced and changes wood fiber properties, it does not significantly affect the quality of paper produced from Gmelina wood.
ESTABLISHMENT OF FRIABLE EMBRYOGENIC (TYPE II) CALLUS FROM IMMATURE TASSELS OF ZEA MAYS (POACEAE)
Authors: Songstad D. D. , Petersen W. L. , Armstrong C. L.
Published: January 2018

Type II callus cultures were initiated from immature tassels of a maize genotype with an A188/B73 genetic background using N6 medium containing 1.0 mg/liter 2,4‐D, 100 mg/liter casamino acids, 25 mM proline, and 0.2% phytagel™. Inclusion of 10 μM AgNO3 in this medium significantly increased the frequency and vigor of the type II callus response. Friable calli emerged from these explants after two consecutive 2‐week subculture intervals. Tassels from 10 to 30 mm long were capable of producing type II cultures. The plants regenerated from these cultures were green and indistinguishable from plants regenerated from immature embryo‐derived calli.
CELL‐ AND TISSUE‐SPECIFIC EXPRESSION OF RICE HISTONE GENE TRANSCRIPTS DURING ANTHER AND POLLEN DEVELOPMENT IN HENBANE (HYOSCYAMUS NIGER)
Authors: Raghavan V. , Jiang Changjun , Bimal Raageeva
Published: January 2018

We have monitored by in situ hybridization the cell‐ and tissue‐specific expression of a rice histone H3 gene during anther and pollen development in henbane (Hyoscyamus niger). Autoradiographic silver grains generated by hybridization of 35S‐labeled antisense probe were present in more or less the same density in all the cells of the anther primordium. During later development of the anther, there was a sequential accumulation of histone mRNA beginning in the epidermis on the outside and ending in the tapetum inside. These changes in transcript abundance in the sporophytic cells of the anther were also related to the stage of microsporogenesis. Transcript level increased during sporogenesis and reached a maximum in mature pollen grains collected from open flowers.
LOCALIZATION OF PHYTOCHROME DURING PEANUT (ARACHIS HYPOGAEA) GYNOPHORE AND OVULE DEVELOPMENT
Authors: Thompson Laura K. , Burgess Candice L. , Skinner Elizabeth N.
Published: January 2018

Previous studies indirectly indicated that phytochrome plays a role in peanut (Arachis hypogaea L. cv. Virginia) gynophore elongation and in ovule and embryo development. Recent advances in the use of monoclonal antibody procedures used in this study have allowed precise localization of phytochrome in the developing peanut gynophore and ovular tissues. Peanut phytochrome from etiolated tissues was found to have a molecular weight of 124 kD as determined by immunoblotting procedures using a monoclonal antibody to pea (Pisum sativum L. cv. Alaska) phytochrome. Immunoblotting procedures revealed that no detectable phytochrome was present in the gynophore tissues or immature ovules during the elongation of the peanut gynophores. After the gynophores penetrated the soil for 8–12 d, phytochrome was detected in increasing amounts in the ovular tissues but not the gynophore tissues. Immunohistological analysis revealed that phytochrome was localized in the developing embryo and adjacent integument tissues. These findings contradict earlier reports that suggested phytochrome was initially present in the gynophore tissues after fertilization where it was believed to inhibit ovular development and stimulate gynophore elongation.
PISTIL DEVELOPMENT AND PARIETAL PLACENTATION IN THE PSEUDOMONOMEROUS OVARY OF ZELKOVA SERRATA (ULMACEAE)
Authors: Okamoto Motoharu , Kosuge Keiko , Fukuoka Nobuyuki
Published: January 2018

Development of female flowers in Zelkova serrata was observed using epi‐illuminated microscopy and scanning electron microscopy, with particular attention given to placentation. After the inception of staminodial primordia, the floral apex becomes flat, and the first and subsequently the second carpel primordia appear at opposite comers of the pistil primordium. Inside each carpel primordium a fossette forms. Through differential growth this depression becomes clear and the carpel wall encircles one side of the future placental region. The placental region is detectable even in early stages, but clear signs of ovule inception appear late when the placental region is elevated onto one side of the ovary wall by intercalary growth. Although the relative size of the two carpels varies among flowers, the placental position always appears to be the border between the two carpels and the floral apex. This suggests that the placentation of Zelkova is parietal. The ovule position in tricarpellate ovaries also suggests an evolutionary derivation from ovaries with parietal placentation. Parietal placentation appears to be the original condition in Urticales.
MAIN ROOT‐LATERAL ROOT JUNCTIONS OF TWO DESERT SUCCULENTS: CHANGES IN AXIAL AND RADIAL COMPONENTS OF HYDRAULIC CONDUCTIVITY DURING DRYING
Authors: North Gretchen B. , Ewers Frank W. , Nobel Park S.
Published: January 2018

The influence of junctions between main roots and lateral roots on water flow was investigated for the desert succulents Agave deserti and Ferocactus acanthodes during 21 d of drying in soil. Under wet conditions, the junctions did not restrict xylem water flow from lateral roots to main roots, consistent with predictions of axial conductance based on vessel diameters. Embolism caused by drying reduced such axial conductance more at the junctions than in adjoining root regions. Connective tracheary elements at the junctions were abundantly pitted and had large areas of unlignified primary wall, apparently making them more susceptible to embolism than vessels or tracheids elsewhere in the roots. Unlike the decrease in axial conductance, the overall hydraulic conductivity of the junction increased during drying because of an increase in the conductivity of the radial pathway. Despite such increases, main roots may not lose substantial amounts of water to a dry soil during drought, initially because embolism at the junctions can limit xylem flow and later because soil hydraulic conductivity decreases. Moreover, the increased root hydraulic conductivity and a potentially rapid recovery from embolism by connective tracheary elements may favor water uptake near the junctions upon soil rewetting.
ENDOCYTOSIS OF LANTHANUM NITRATE IN THE ORGANIC ACID‐SECRETING TRICHOMES OF CHICKPEA (CICER ARIETINUM L.)
Authors: Lazzaro Mark D. , Thomson William W.
Published: January 2018

The organic acid‐secreting trichomes of chickpea (Cicer arietinum L.) were exposed to 2.5 mm lanthanum nitrate for 24 hr, and this concentration did not inhibit trichome secretion compared with that of controls. We subsequently used this nontoxic concentration of lanthanum to examine endocytosis. In the stalk cells of these secretory trichomes, exogenously applied lanthanum nitrate was present in cell walls and vacuoles, as well as within both invaginations in the plasma membrane and vesicles in the peripheral cytoplasm between the plasma membrane and the tonoplast. In the head cells, lanthanum nitrate was present in cell walls and in vesicles that form a layer in the cytoplasm around the edge of the head cells, but was not present in vacuoles. We propose that fluid phase endocytosis targeted to the vacuole takes place in the stalk cells and that endocytosis occurs in the head cells to remove excess plasma membrane after the fusion of secretory vesicles with the plasma membrane. This is the first demonstration of endocytosis in secretory trichomes.
A NEW SPECIES OF BLACK OAK (QUERCUS, SUBG. ERYTHROBALANUS, FAGACEAE) FROM THE SIERRA MADRE OCCIDENTAL, MEXICO
Authors: Spellenberg Richard
Published: January 2018

Quercus mcvaughii is described as a new species of black oak (subgenus Erythrobalanus) from the Sierra Madre Occidental, in northern Durango and western Chihuahua, Mexico. It is most closely related to the more southern Q. crassifolia. Sessile or subsessile hairs, usually of different sizes, on the abaxial leaf surface distinguish Q. mcvaughii from Q. crassifolia, where hairs are similar in size and conspicuously stipitate. A key is provided for distinguishing similar species in the region. Intergradation of Q. mcvaughii with Q. crassifolia, Q. hypoleucoides, and Q. sideroxyla is reported.
POTENTIAL FOR THE LOSS OF SELF‐INCOMPATIBILITY IN POLLEN‐LIMITED POPULATIONS OF MAYAPPLE (PODOPHYLLUM PELTATUM)
Authors: Whisler Sandra L. , Snow Allison A.
Published: January 2018

Self‐compatibility (SC) appears to be a derived trait in many unrelated taxa. A major selective force that could lead to the evolution of SC from self‐incompatibility (SI) is inadequate pollination. Here we show that seed set is strongly pollenlimited in populations of mayapple, Podophyllum peltatum (Berberidaceae). Hand‐pollination led to a 26‐fold increase in seed set as compared to natural levels in 1989, and to a fivefold increase in 1990. The species is SI, but in a survey of 49 colonies in Ohio we found three that had more than 50% fruit set from self pollen (as compared to about 90% fruit set from hand‐outcrossed flowers). However, when hand‐selfing yielded fruits, the number of seeds per fruit was only about 10% of the seed set from hand‐outcrossing. We discuss the relative fecundity of putative SC and SI genotypes in terms of conditions needed for the spread of SC in mayapple populations (little or no morphological change would be needed to ensure within‐flower selfing). Seed set from putative SC genotypes appeared to be low enough to prevent them from replacing SI genotypes, even in the face of infrequent pollinator visits.
GENETIC DIVERSITY IN GOSSYPIUM HIRSUTUM AND THE ORIGIN OF UPLAND COTTON
Authors: Wendel Jonathan F. , Brubaker Curt L. , Percival A. Edward
Published: January 2018

Gossypium hirsutum has a large indigenous range encompassing most of Mesoamerica and the Caribbean, where it exhibits a diverse array of morphological forms spanning the wild‐to‐domesticated continuum. Modem, highly improved varieties (“Upland cotton”), which currently account for about 90% of world cotton commerce, are day‐length neutral annuals derived from subtropical, perennial antecedents. To assess levels and patterns of genetic variation in the species and to elucidate the origin of Upland cotton, 538 accessions representing the full spectrum of morphological and geographical diversity were analyzed forallozyme variation at 50 loci. Levels of variation are modest overall but are low in Upland cotton. Relationships among accessions reflect pre‐Columbian influences of aboriginal peoples and later European colonists superimposed on the preagricultural pattern. In contrast to expectations, two centers of diversity are evident, one in southern Mexico‐Guatemala and the other in the Caribbean. Introgression of G. barbadense genes into G. hirsutum has been common in a broad area of sympatry in the Caribbean. The germplasm of present cultivars traces to Mexican highland stocks, which, in turn, were derived from material originally from southern Mexico and Guatemala. Despite the widespread belief that germplasm from several other species has been incorporated into modem Upland stocks through intentional breeding efforts, the 50 Upland cultivars examined contain no unique alleles, suggesting that retention of genes from transspecific sources has been minimal. The most recent infraspecific treatment, which recognizes seven races, does not adequately represent genetic relationships.
ADVANTAGES OF BEING A SPECIALIST FEMALE IN NODIOECIOUS SILENE VULGARIS S.L. (CARYOPHYLLACEAE)
Authors: Pettersson Mats W.
Published: January 2018

According to sex allocation theory, to maintain a mutant male‐sterile plant in a population of hermaphrodites such a plant must compensate its loss of fitness caused by inhibition of pollen production with a higher reproductive success through its female function. In the present study of a gynodioecious population of Silene vulgaris (Caryophyllaceae) I show that hermaphrodites not only benefit from outcrossing, in that progeny from outcrossed flowers are more vigorous than those from selfed flowers within an individual plant, but they also suffer heavily from self‐pollination between different flowers of the same individuals, which could be demonstrated in experimentally made male‐sterile (emasculated) individuals. Seeds from the emasculation period were heavier and germinated better than when the same individual was an intact hermaphrodite. Naturally male‐sterile (female) individuals produced more fruits due to flowers staying open longer for pollen to arrive via some vector. However, the higher seed number alone could not provide the fitness advantage needed for females to be maintained in the population, but females also produced heavier seeds as compared to the hermaphrodites. Differences in seed survival and seedling establishment in the field are expected to add the advantages necessary for female plants to be selectively plausible.
SEED MORPHOLOGY AND SYSTEMATICS OF MENYANTHACEAE
Authors: Chuang T. I. , Ornduff Robert
Published: January 2018

Scanning electron microscopic investigations of seed morphology of the five genera of Menyanthaceae illustrate a remarkable diversity of seed characteristics for a small family. Seeds of the monotypic northern hemisphere Menyanthes and Fauria are unomamented and similar, and those of the monotypic Liparophyllum of New Zealand and Tasmania are similar to some Australian species of Villarsia. Seed characteristics within the larger genera Villarsia and Nymphoides are variable and mostly species specific, but do not lend support to taxonomic separation of these genera. Interspecific affinities postulated on other grounds are, in many instances, supported by seed morphology. Various seed‐coat features are believed to aid in water or animal dispersal of the seeds of several species. Ant dispersal appears to be important for Villarsia and Nymphoides in Australia, but does not seem to occur in these genera or in other members of the family outside of Australia.
EMBRYO SAC DEVELOPMENT IN SOYBEAN: THE CENTRAL CELL AND ASPECTS OF FERTILIZATION
Authors: Folsom Michael W. , Cass David D.
Published: January 2018

Development of the soybean central cell and events associated with fertilization are described. Central cell development involves the simultaneous formation of numerous multigrain amyloplasts, development of wall ingrowths, reduction of the cell's major vacuole, and nuclear migration. As these processes reach completion, a phase of lytic activity begins. This activity ultimately results in both the breakdown of most multigrain amyloplasts in the central cell and the reestablishment of the cell's large vacuole. While these processes occur, the egg and synergid cells continue development. Examination of the egg apparatus after plasmogamy but prior to karyogamy reveals several changes. Whereas the synergid containing the pollen tube is degenerate and the distribution of organelles in the persistent synergid has changed, the egg cell with a free sperm nucleus exhibits higher levels of metabolite storage and changes in its wall structure. The walls of the newly formed sporophyte are similar to those of egg apparatus cells (Folsom and Cass, Canadian Journal of Botany 68: 2135–2147 [1990]) in that they seem to lack a middle lamella. This layer becomes apparent only in the two‐celled proembryo. While these changes occur in the egg, zygote, and proembryo, synergids undergo different degradative pathways.
A COMPARISON OF FLORAL DEVELOPMENT IN WILD TYPE AND A HOMEOTIC SEPALOID PETAL MUTANT OF CLARKIA TEMBLORIENSIS (ONAGRACEAE)
Authors: Smith‐Huerta Nancy L.
Published: January 2018

The mature wild type petals of Clarkia tembloriensis consist of a long slender claw and an expanded deltoid‐shaped limb. They are pink, with a maroon spot at the base of the limb. Their surface texture is smooth. A variant of petal form, crinkled petal, occurs commonly in several natural populations of C. tembloriensis. The mature crinkled petals are elongated, greenish pink, and possess trichomes. They resemble the mature sepals of C. tembloriensis in general shape, color, and surface texture. Organ initiation and subsequent patterns of development of wild type petals, wild type sepals, and crinkled petals were examined and compared using scanning electron microscopy and allometric growth analysis. Crinkled petals are similar to wild type petals in time and position of primordia initiation, and in size and shape at inception. Crinkled petals are similar to wild type sepals in pattern of allometric growth. The crinkled petal mutant fits the broad definition of a homeotic mutant in that the petal has assumed characteristics of the sepal.
IMMUNOCYTOCHEMICAL LOCALIZATION OF δ‐ZEIN IN THE PROTEIN BODIES OF MAIZE ENDOSPERM CELLS
Authors: Esen Asim , Stetler David A.
Published: January 2018

The δ‐zein, a minor component of the maize prolamin, shows extensive immunological cross‐reactivity with α‐ and β‐zeins. The adsorption of an anti‐δ‐zein serum sequentially with cross‐reacting antigens revealed that only about 18% of the reactivity of the antiserum was directed to epitopes unique to δ‐zein. The localization of the various zein classes within the protein bodies of endosperm cells is important to understanding the synthesis, sequestering, and utilization of these storage proteins. Sections of 28 days after pollination (DAP) isolated protein bodies and 18 and 40 DAP whole endosperms were reacted sequentially with whole anti‐δ‐zein serum and gold‐conjugated protein A. The results showed intense gold labeling in the core (inside the peripheral zone) and weak labeling in the periphery of the sections. This localization was not definitive in view of the above‐mentioned cross‐reactivities. To obtain an unequivocal localization, the whole antiserum was adsorbed with α‐, β‐, and γ‐zeins and rendered monospecific for δ‐zein. Immunostaining of protein body sections with monospecific antiserum showed that gold label was exclusively in the core region of the protein body and appeared to be in discrete lines and zones especially in 18 DAP protein bodies. The data from localizations using the monospecific antiserum indicated that δ‐zein occurs throughout the core region of the protein body, probably interspersed with α‐ and β‐zeins. The location of δ‐zein is consistent with that predicted from its order of degradation during seed germination.
POPULATION DEMOGRAPHY OF PASTINACA SATIVA (APIACEAE): EFFECTS OF SEED MASS ON EMERGENCE, SURVIVAL, AND RECRUITMENT
Authors: Hendrix Stephen D. , Trapp E. Joseph
Published: January 2018

The effect of seed mass on emergence, survival, and recruitment to flowering in Pastinaca sativa, a species that produces progressively smaller seeds on the primary, secondary, and tertiary umbels, was analyzed in two field experiments begun in 1982 and 1983. In both experiments, overall emergence was positively related to seed mass, but the effects of seed mass on emergence in fall cohorts was relatively unimportant. Initial seed mass was positively related to overwintering survival in one experiment but not the other, possibly due to differences in winter conditions. Survival to flowering was positively related to seed mass in the 1982 experiment but negatively related to seed mass in the 1983 experiment. This difference is due to greater survival of seedlings from small seeds during short‐term droughts, a previously unrecognized advantage of small seeds. Because of differences in survival in the two experiments, recruitment (number of flowering plants/number of seeds sown) was positively related to seed mass in the 1982 experiment but not in the 1983 experiment. The effects of timing of emergence on survival generally disappeared within 12 months. Our results suggest that the relationship between initial seed mass and recruitment in Pastinaca represents a distribution of outcomes, variable from year to year. However, because short‐term droughts in Iowa are common, we hypothesize that in most years, seed mass has little impact on recruitment. Furthermore, small scale heterogeneity may often overwhelm any potential effects of seed mass and timing of emergence on recruitment.
INFLUENCE OF SUPPLEMENTAL INORGANIC NUTRIENTS ON GROWTH, SURVIVORSHIP, AND MYCORRHIZAL RELATIONSHIPS OF SCHIZACHYRIUM SCOPARIUM (POACEAE) GROWN IN FUMIGATED AND UNFUMIGATED SOIL
Authors: Anderson Roger C. , Liberta Anthony E.
Published: January 2018

Little bluestem grass Schizachyrium scoparium ([Michx.] Nash) plants were grown under field conditions for 2 years in soils fumigated with methyl bromide and chloropicrin, or in unfumigated soil, and treated with supplemental inorganic nutrients (bases calcium and magnesium) phosphorus, nitrogen, and potassium. Most differences in measured plant responses were due to interactions between fumigation and nutrient treatments. These included biomass production, root mass per unit length (μg/cm), root lengths, flowering culm production, percent colonization, colonized root length, and spore production in rhizosphere soil. Plants generally responded to mycorrhizal fungal colonization by reducing total root length and producing thicker roots. Treatment of plants with bases appeared to profoundly affect the mycorrhizal association by reducing sporulation of vesicular‐arbuscular mycorrhizal fungi and increasing colonization. When fumigated or unfumigated soils were considered separately, base‐treated plants produced more biomass than other treatments. Base‐treated plants grown on unfumigated soil had more flowering culms and longer colonized root lengths than all other plants. Percent colonization by mycorrhizal fungi and colonized root length were positively correlated with phosphorus/nitrogen ratios, but the ratio was not correlated with plant biomass production. This suggests that phosphorus is not a limiting nutrient in our soil and investment in a mycorrhizal association may not result in enhanced plant growth. The base‐nutrient effects may indicate a need to reevaluate earlier studies of macro nutrient effects that did not take into account the role played by calcium and magnesium in assessing fungus‐host plant interactions.
EFFICACY OF WIND POLLINATION: POLLEN LOAD SIZE AND NATURAL MICROGAMETOPHYTE POPULATIONS IN WIND‐POLLINATED STABEROHA BANKSII (RESTIONACEAE)
Authors: Honig Marijke A. , Linder H. P. , Bond William J.
Published: January 2018

A detailed examination was made of the numbers of pollen grains and microgametophytes occurring on stigmas of a dioecious, wind‐pollinated species, Staberoha banksii. The number of pollen grains per pistil ranged from 0 to over 100; and the mean pollen load size per pistil per plant varied from 4.4 to 28. Distance to the fourth nearest male plant was used as a measure of local pollen availability and accounted for 63.5% of the between‐plant variation in pollen load size. In contrast, the number of microgametophytes did not show a leptokurtic decline with increasing distance from a pollen source. On average there were 5.19 microgametophytes per ovule, which is higher than all comparable data for insect‐pollinated taxa, and 66% of the stigmas had two or more microgametophytes. Given that there is a single ovule per flower, there is considerable potential for gametophytic competition. Seedset was very high, averaging 93%, and showed no significant decline in isolated female plants. We suggest that the quantity of pollen is not limiting fertilization in this population and that wind may therefore be highly effective as a pollen vector.
NEW CHROMOSOME COUNTS FOR CHUSQUEA AND AULONEMIA (POACEAE: BAMBUSOIDEAE)
Authors: Pohl Richard W. , Clark Lynn G.
Published: January 2018

Tetraploid chromosome counts of n = 20 are reported for two previously cytologically unknown South American species of Chusquea, C. capitulifora and C. scandens. Diploid counts were previously unknown in this genus, but C. talamancensis of Costa Rica has n = 10. No previous chromosome counts were known for the genus Aulonemia nor any other genus of the subtribe Arthrostylidiinae. Aulonemia pumila and A. amplissima from South America are tetraploid with n = 20.
ASSOCIATION OF FOUR DIFFERENT CALCIUM CRYSTALS IN THE ANTHER CONNECTIVE TISSUE AND HYPODERMAL STOMIUM OF CAPSICUM ANNUUM (SOLANACEAE) DURING MICROSPOROGENESIS
Authors: Horner Harry T. , Wagner Bruce L.
Published: January 2018

The anther connective tissue and hypodermal stomium between adjacent locules in the anthers of Capsicum annuum L. (Solanaceae) are the sites of formation of calcium salt crystals with four different habits. The spatial and temporal associations of these crystals and the idioblastic cells in which they form indicate that crystal sand occurs earliest in anther development near the single vascular strand, followed by spherulites and prismatic crystals farther out in the connective tissue, and finally druses occur in the hypodermal stomium. Both the druses and the crystal sand crystals are encased in crystal chambers and are associated with distinct membranes, whereas the spherulites and prismatic crystals are not bounded by any apparent membranes but they are surrounded by dense material that is rich in calcium and stains positively for polysaccharides and proteins. Quite often spherulites and prismatic crystals are observed within a single cell in contact with each other. X‐ray diffraction of crystal preparations containing all four crystal habits and X‐ray elemental analyses of single crystals, as well as visual observations and acid treatments, suggest that all four crystal habits consist of calcium oxalate. The hypodermal stomium and adjacent connective tissue degenerate at the pollen stage causing adjacent locules to fuse. Shortly afterward, each stomium epidermis splits open along the length of the anther releasing the pollen. It is suggested that the crystal idioblasts are involved in this process, possibly by a temporally orchestrated sequestration of calcium from both the cell cytoplasm and cell wall.