bluuebunny/crossref_metadata_2025 huggingface dataset:
DEPENDENCY OF THE TENSILE MODULUS ON TRANSVERSE DIMENSIONS, WATER POTENTIAL, AND CELL NUMBER OF PITH PARENCHYMA
Authors: Niklas Karl J.
Published: January 2018

Uniaxial tensile tests of solid and hollow cylindrical plugs of pith parenchyma from potato tubers indicate the tensile modulus of elasticity, E, can vary significantly as a function of tissue transverse area and water potential. E increases from 1.2 to 19 MPa as ψw changes from ‐1.4 to ‐0.4 MPa. E increases from 5 to 19 MPa as transverse area of solid tissue sample increases from 0.2 to 2.5 cm2. Variations in E accompanying changes in transverse area appear to be related to cell number along the radii of plugs. Hollow cylindrical plugs for which wall thickness is maintained but total tissue area is changed show constant values of E. It is suggested that shear stresses within tissue samples influence E and are dependent upon cell number and tissue water content. Material with these properties would be a “poor choice” for constructing plant organs experiencing repeated stress and periodic dehydration. However, ground tissue may act as a buffer against localized ovaling of stem and leaf cross sections under loading.
VARIATION IN LEAF DISSECTION AND LEAF ENERGY BUDGETS AMONG POPULATIONS OF ACHILLEA FROM AN ALTITUDINAL GRADIENT
Authors: Gurevitch Jessica
Published: January 2018

The degree of leaf dissection differs dramatically among populations of the Achillea millefolium complex along an altitudinal gradient in the Sierra Nevada. The purpose of this study was to determine whether there was a genetic basis to differences in leaf shape among populations, and also to determine the importance of genetic variability within populations, plastic responses of leaf shape to the growth environment, and genetic differences among populations in plastic response to the environment. A second major goal of the research was to investigate the effects of differences in leaf dissection on the capacity for leaf temperatures to become uncoupled from air temperatures. Greenhouse experiments using clonal replicates of plants collected at different altitudes revealed that there were genetic differences among populations in the degree of dissection, and that other sources of phenotypic variation, such as plasticity, were also significant. Leaves from the highest altitude population had the most compact shape under all conditions, while those from lower altitude populations were always more open and highly dissected. In both simulations and actual measurements the dissected leaves of low altitude plants remained close to air temperatures, while the compact leaves of high altitude plants had the capacity to warm up substantially above air temperatures.
ORGANIC MATTER DYNAMICS IN FOUR SEASONALLY FLOODED FOREST COMMUNITIES OF THE DISMAL SWAMP
Authors: Megonigal J. Patrick , Day Frank P.
Published: January 2018

Budgets of organic matter dynamics for plant communities of the Great Dismal Swamp were developed to summarize an extensive data base, determine patterns of biomass allocation, transfer and accumulation, and make comparisons with other forested wetlands. Aboveground net primary production on the flooded sites (1,050–1,176 g m‐2 yr‐1) was significantly greater than on a rarely flooded site (831 g m‐2 yr‐1). Estimates of belowground net primary production were comparable to aboveground production on flooded sites (824–1,221 gm‐2 yr‐1). However, productivity was nearly three times greater belowground than aboveground on the rarely flooded site (2,256 g m‐2 yr‐1). Aboveground productivity in Dismal Swamp forests is relatively high compared to other forested wetlands. This is attributed to the timing and periodic nature of flood events. Fine root turnover is shown to be an important source of soil organic matter. Estimates indicate that roots contribute about 60% of the annual increment to soil organic matter. Leaflitter contributes 6–28% and wood debris contributes 5–15%. Comparisons with other forested wetlands suggest that detritus accounts for greater than half of the total organic matter (living + dead) in many wetland systems.
CONTRASTING PHOTOSYNTHETIC BEHAVIOR IN LEAVES AND TWIGS OF HYMENOCLEA SALSOLA, A GREEN‐TWIGGED WARM DESERT SHRUB
Authors: Comstock Jonathan P. , Ehleringer James R.
Published: January 2018

The photosynthetic behavior of leaves and twigs was compared in Hymenoclea salsola T. and G., a subshrub of the Mohave and Sonoran deserts, in which both leaves and green twigs make substantial contributions to whole‐plant carbon gain. Light saturated photosynthesis in twigs was 0.62 times that of leaves (36.9 μmol m‐2 s‐1) when plants were well watered. Similar ratios were consistently observed in contrasting the photosynthetic responses of the two organ types to light, temperature, and intercellular CO2, regardless of whether rates were compared under saturating or highly limiting conditions of light or intercellular CO2. These scalar differences in photosynthetic rate between leaves and green twigs under a wide range of conditions were correlated with contrasting anatomical features such as chlorenchyma volume per projected area. Under normal ambient CO2 concentrations (350 μl 1‐1), twigs on well watered plants operated at lower intercellular CO2 concentrations than the leaves. Possible causes of this difference are discussed with respect to performance under well‐watered conditions, organ lifespans, and contrasting anatomical constraints. Twigs require larger investments than do leaves of both carbon and nitrogen per projected area of the respective organs, yet they realize lower photosynthetic rates per intercepted light. Twigs, however, fulfill additional roles besides photosynthesis such as structural support and vascular transport which does not allow them to be as anatomically specialized as leaves for photosynthesis. Twigs also have a longer expected lifespan than leaves with a larger fraction of them surviving the summer drought period. This was correlated with a greater tolerance of twig than leaf photosynthesis to low plant water potentials.
POLLINATION OF THE ARROYO WILLOW, SALIX LASIOLEPIS: ROLE OF INSECTS AND WIND
Authors: Sacchi Christopher F. , Price Peter W.
Published: January 2018

We studied the relative roles of insects and wind as pollen vectors for the arroyo willow,Salix lasiolepisBenth. through insect exclosure studies at two elevational sites. Insect pollination resulted in production of 99.9% of seeds at a low elevation site (2,130 m) and at a high elevation site (2,450 m) with wind playing an exceedingly small role. Few pollen grains reached individual pistillate catkins despite the presence of abundant airborne willow pollen near male plants. In flowers that showed evidence of receipt of wind transferred pollen, due to their swollen appearance, we found only 1.74 fertilized ovules per flower and that 90.9% of these fertilized ovules were aborted by the maternal plant. In contrast, flowers open to insect visitation possessed 7.00 fertilized ovules per flower, 83.3% of which became filled seeds. We tested for the existence of apomictic seed production through use of closed bags that excluded both insect‐and wind‐transferred pollen but found no evidence of seed produced in this treatment. Additional control studies documented that wind treatment bags did not impede pollen flow while neither wind or closed bags influenced seed set in our treatments.
EMBRYOLOGICAL DEVELOPMENT OF LACHNANTHES CAROLINIANA (HAEMODORACEAE)
Authors: Simpson Michael G.
Published: January 2018

Embryological development of Lachnanthes caroliniana was studied utilizing standard anatomical techniques and SEM. Lachnanthes has a monocotyledonous anther wall development (endothecial cells with spiral secondary wall thickenings), successive microsporogenesis, and amoeboid (periplasmodial) tapetal development. Mature pollen grains are 2‐nucleate with a proximal, fusiform generative cell. Ovules are initiated as 5–7 cylindrical primordia from a common placental base. Basal ovular swellings collectively contribute to the enlarged, peltate placenta. Mature ovules are pleurotropous, anatropous, bitegmic, and crassinucellate; the nucellus consists of a chalazal hypostase, radially elongate lateral cells, and a prominent micropylar nucellar cap. Megasporogenesis is successive, forming a linear tetrad of megaspores. Megagametogenesis is monosporic; the female gametophyte is of the Polygonum‐type with relatively large, pyriform antipodals. Endosperm formation is helobial, resulting in the establishment of a ring of four thick‐walled basal endosperm cells (the chalazal chamber) and numerous free nuclei (in the micropylar chamber). The mature cellular endosperm is filled with starch grains and has a chalazal cavity and a thick‐walled peripheral layer. The discoid, peltately attached seeds have marginal wings derived by anticlinal divisions and buckling of the outer integument alone. Inner and middle cuticular layers are present in the seed coat. Lachnanthes is similar to all other investigated members of the Haemodoraceae in major embryological features. The significance of embryological evidence with regard to interfamilial classification is discussed. Future studies of ovule and seed development may prove valuable in phylogenetic studies in assessing the homology of placental, ovule, and seed morphology and anatomy.
FOLIAR MORPHOLOGY AND ANATOMY OF THE GIGANTOPTERID PLANT DELNORTEA ABBOTTIAE, FROM THE LOWER PERMIAN OF WEST TEXAS
Authors: Mamay Sergius H. , Miller John M. , Rohr David M. , Stein William E.
Published: January 2018

Delnortea is a monotypic genus (type‐species: D. abbottiae) of Lower Permian gymnosperms based on leaves from uppermost Leonardian deltaic sediments exposed in the Del Norte Mountains, West Texas. The leaves are simple, symmetrical, mostly oblong or elliptical, and vary in length from 1.2 to about 35 cm. The petioles are short and stout, with a basally enlarged abscission zone. The margins are crenate, with a narrow, indurated border. Venation is in 4 orders: the secondaries and tertiaries are robust, unbranched, and pinnately arranged in a precise “herringbone” pattern, with the secondaries ending in the marginal sinuses; the quaternaries divide sparingly and fuse with others to form a dense reticulum of small meshes. Permineralized petiole and midrib material reflects a bifacial cambium, shown by a semicircular vascular arc, irregularly divided into several collateral bundles with secondary xylem and phloem. Delnortea is referable to the Gigantopteridaceae, a probably artificial family of gymnosperms incertae sedis with important venation features in common, but without known diagnostic reproductive organs. With Delnortea, the North American gigantopterids now include 5 genera, but Gigantopteris itself is lacking. Delnortea holds a relatively advanced evolutionary position among the American gigantopterids; its leaf morphology and gymnospermous anatomy entail intriguing points of comparison with Gnetum. The limited geographic and stratigraphic ranges and morphological distinctiveness of the American gigantopterids and associated taxa attest to rapid evolution and dispersal from a small area of origin in the southwestern United States during Leonardian time.
TRANSMISSION GENETICS OF ISOZYME LOCI IN RAPHANUS SATIVUS (BRASSICACEAE): STRESS‐DEPENDENT NON‐MENDELIAN SEGREGATION
Authors: Ellstrand N. , Devlin B.
Published: January 2018

Deviations from Mendelian ratios are frequently treated as an intrinsic property of individuals, independent of the environment. We tested whether the environment of the parents could alter patterns of inheritance in the wild radish, Raphanus sativus. We demonstrated the genetic basis of 12 isozyme loci by controlled pollinations of unstressed plants. The frequency of deviant segregation detected was not different than that expected by chance. Controlled pollinations among stressed plants showed over 3 times as much deviant segregation as the unstressed controls. No genetic correlates of segregation bias were detected. Linkage was assessed for 64 of the 66 pairs of loci. Two linkage groups were detected, one involving four loci (PGM2–ACO–ACP–LAP), the other involving a single pair (EST‐PRX). The second linkage group is apparently associated with a locus or tightly linked loci which may segregate for “balanced” lethals on the same chromosome. Deviant segregation did not appear to act primarily by selection on a particular gamete. Postzygotic selection was the probable source of at least some of the aberrant segregation. Because no particular allele was favored in such situations, selection is apparently operating on alleles at linked loci rather than on the allozyme loci per se. Data from other studies on wild radish support the suggestion that postzygotic selection might be an important influence on progeny segregation ratios. Because wild radishes often encounter a variety of stresses in the field, in this species, aberrant segregation may be common under natural conditions.
THERMOMORPHOGENESIS IN LILIUM LONGIFLORUM
Authors: Erwin John E. , Heins Royal D. , Karlsson Meriam G.
Published: January 2018

Stem elongation and leaf orientation in Lilium longiflorum Thunb. were influenced more by the difference (DIF) between day temperature (DT) and night temperature (NT) than absolute DT or NT from 14 to 30 C. Plant height and internode length increased 129 and 382%, respectively, as DIF (DT‐NT) increased from –16 to 16 C as compared to only 15 and 58% when either DT or NT was increased from 14 to 30 C, respectively. Leaf orientation, defined as the angle between a line perpendicular to the stem and the line from the leaf base to the leaf tip, increased 43° (leaves became more upright) as DIF increased from –16 to 16 C. In contrast to plant height, internode length, and leaf orientation, leaf and flower length were influenced more by absolute temperature than DIF. Leaf and flower length decreased 32 and 14%, respectively, as NT increased from 14 to 30 C. DT had little effect on either leaf or flower length. The influence of DIF on stem elongation suggested that thermomorphogenesis was not a function of total plant carbohydrate or carbohydrate translocation. Instead, DIF appeared to influence the endogenous gibberellin content or the response of plant tissue to gibberellin. Similarities between thermomorphogenic plant responses and photomorphogenic plant responses suggested that these two processes may be related with respect to their perception and/or transduction.
SPATIAL AND TEMPORAL VARIATION IN THE SEED BANK OF A SEMIARID GRASSLAND
Authors: Coffin Debra P. , Lauenroth William K.
Published: January 2018

The spatial and temporal variability in the seed bank of a semiarid grassland in Colorado was evaluated using soil cores. Spatial variability in the soil storage of germinable seeds was assessed by sampling two shortgrass plant communities on sites with the same climatic conditions but differing in soil texture. Differences between communities were largely the result of annual plant seeds. Eight sampling dates over two years were used to assess temporal variability, which was more important to the storage of germinable seeds than spatial variability. Differences in the numbers of seeds stored were found between the two sampling years, and seasonally within years. The number of seedlings that emerged from the samples ranged from 122–2,748/m2. A poor correspondence was found between the species composition of the plant communities and the storage of germinable seeds; however, the species composition of the seeds produced on the sites tended to have a high similarity with the seedlings that emerged. Most of the species had a transient rather than a persistent presence in the seed bank.
EFFECTS OF AGE AND SIZE ON LIFE HISTORIES AND POPULATION GROWTH OF RHODODENDRON MAXIMUM SHOOTS
Authors: McGraw James B.
Published: January 2018

Age‐ and size‐specific shoot life histories were studied with population censuses in June 1984 and June 1985 in an evergreen understory shrub. Rhododendron maximum. Most shoots (65%) survived without branching or flowering, and lesser numbers branched (2%), flowered (20%), or died (23%) during the year between censuses. The probabilities of surviving, branching, flowering or dying were both age‐ and size‐dependent. Small, young shoots increased in leaf area. Flowering occurred most prominently in 3‐ to 6‐year old shoots that had exceeded a leaf area of 200 cm2, and the rate of flowering increased proportionately with size above this threshold. Branching normally occurred in the year following flowering. The age and size distributions of the population shifted significantly between years, indicating a nonequilibrium population. The survival schedule was Deevey Type I, indicating a high degree of “parental care” of young shoots. Age‐ and age + size‐based demographic models predicted a rapid decline of the shoot population over a decade, while a size‐based model predicted a much slower decline in shoot numbers. A sensitivity analysis of the models showed that overall shoot population growth was positively influenced by branching shoots and shoots that added leaf area, and negatively influenced by shoots that lost leaf area, died, or flowered. The role of shoot life histories in determining individual plant fitness and ecological dominance is discussed.
INTERACTION BETWEEN CRYPTOCHROME AND PHYTOCHROME IN HIGHER PLANT PHOTOMORPHOGENESIS
Authors: Mancinelli Alberto L.
Published: January 2018

At least three photoreceptors are involved in the mediation of light action in higher plant photomorphogenesis: cryptochrome (UV‐A/blue light photoreceptor), UV‐B photoreceptor, and phytochrome. The degree of photoreceptor interaction in photomorphogenesis can apparently vary depending on the response, the species, and the stage of development of the biological system. In most cases of interaction studied so far, Pfr, the physiologically active form of phytochrome, is apparently required for the final expression of the response. In some systems, the cryptochrome and/or UV‐B photoreceptor mediated action of UV/blue radiation is required to establish/enhance/maintain responsiveness toward Pfr. There is no evidence for photoreceptor interaction in some response‐system combinations. It is not known for sure if this apparent lack of photoreceptor interaction represents a real situation or just a failure to detect it because of experimental limitations. Practically nothing is known about the mechanism of photoreceptor interaction at the molecular level.
PATTERNS OF PLANT ONTOGENY THAT MAY INFLUENCE GENOMIC STASIS
Authors: Klekowski Edward J. , Kazarinova‐Fukshansky Nina , Fukshansky Leonid
Published: January 2018

It is an axiom in biology that genes control the ontogeny and ultimately the final form of an organism. In plants a given morphological form can often arise through more than one ontogenetic pattern of cell divisions. Different ontogenetic patterns have different properties with regard to the final age in cell divisions of the initials in the meristems for a given morphological form. If mutation per genome per cell division is an important biological metric, then since the age of a cell in cell divisions is a function of ontogeny, the cellular ontogeny will influence the degree of mutation‐loading in meristematic initials. Thus, ontogeny and form may affect the genes (by promoting or lessening genomic stasis) as well as, of course, being determined by the genes. This paper explores mathematically the relationship between different patterns of cell division and mutation‐loading.
COMPONENTS OF SEED AND POLLEN YIELD OF LOBELIA CARDINALIS: VARIATION AND CORRELATIONS
Authors: Devlin B.
Published: January 2018

Plants from three Lobelia cardinalis populations were grown under common garden conditions to assess intra‐ and interplant variation in seed and pollen production. Seed number per flower and mean seed weight varied systematically with floral position on the inflorescence (lowest values were from terminal flowers) but pollen grain number per flower did not vary systematically with floral position. Most of the remaining variance in seed and pollen grain number per flower and mean seed weight was distributed among plants; clones produced very similar amounts of pollen and seed. Seed yield was positively correlated with seed production per flower and with total flower production, but not with mean seed weight; pollen yield was also positively correlated with pollen grain production per flower and total flower production. Seed and pollen yield were simple linear functions of plant size but only pollen yield was a simple linear function of flower production; seed yield was a quadratic function in which the second order term was negative. This quadratic relationship resulted from a negative correlation between seed number per flower and total flower production. This correlation, in addition to the wide variation among plants in pollen number per flower, accounts for the weak correlation of seed and pollen yield. I conclude from these data that it is unlikely that plants in natural L. cardinalis populations transmit genes to the population's seed crop equally through pollen and ovules—emphasizing the importance of measuring both male and female components of reproductive success.
SEED BANK, SURVIVORSHIP, AND SIZE DISTRIBUTION OF A NEBRASKA POPULATION OF IMPATIENS CAPENSIS (BALSAMINACEAE)
Authors: Antlfinger Ann E.
Published: January 2018

The growth and survivorship of a population of Impatiens capensis were followed in eastern Nebraska. Soil cores were taken within the population to estimate the size of the seed bank. The number of seeds in the soil remained relatively constant from April through October, with a mean of 200 seeds/m2. The seed bank size corresponded to observed seedling densities in the following years. Twenty permanent plots were established within the population and censused for three years, 1983–1985. Seedling recruitment to the population was similar in 1983 and 1984 but 30% higher in 1985. The seedling densities of plots were uncorrelated from year to year. Survivorship in 1983 followed a Deevey Type I pattern. Almost one‐third of the population survived until chasmogamous reproduction. Plant size (stem height) was measured monthly on all individuals during 1983. The frequency distribution of stem height was positively skewed as long as growth was exponential. When the growth rate slowed, the distribution became more normal.
INTRASPECIFIC VARIATION IN POLLEN YIELD IN BROMEGRASS (POACEAE: BROMUS)
Authors: McKone Mark J.
Published: January 2018

Variation in pollen production was measured within five hermaphrodite species of bromegrass (Bromus). Anther length is an excellent predictor of pollen production in this genus (R2 = 0.97). Anther length varied considerably within each of the species, both among and within individual plants. Within plants, most of the variation occurred among florets within spikelets; florets in upper spikelet positions were smaller and produced less pollen. In B. inermis, pollen production was decreased by defoliation and increased in shoots that grew on thatching ant (Formica obscuripes) mounds. Whole‐shoot pollen yield was determined by spikelet number, number of florets per spikelet, and pollen production per floret. All of these yield components must be considered in attempts to estimate pollen production accurately.
GROWTH RESPONSES FROM WHOLE FRUIT AND FRUIT HALVES OF LEMON CULTURED IN VITRO
Authors: Tisserat Brent , Jones Danny , Galletta Paul D.
Published: January 2018

A comparative growth study was conducted on juice vesicles cultured in the form of various fruit explant types (equatorially bissected fruit halves, longitudinally bissected fruit halves, one‐eighth sections of fruit, one‐quarter sections of fruit, whole carpel segments, 2 or 3 mm thick equatorial slices of fruit, and 1 cm2 fruit endocarp pieces) from 15 mm diam Citrus limon (L.) Burm. f. cv. Eureka lemons. Juice vesicles within equatorial fruit halves produced the least amount of callus. Furthermore, these juice vesicles grew similarly to juice vesicles occurring in the tree grown fruit. A study of cultured equatorial fruit halves using 10–45 mm diam lemons was then conducted. Fruit half cultures containing juice vesicles could be readily established from 15–45 mm diam lemons. Vesicles from 10 mm diam fruit halves, however, invariably produced callus. Vesicles cultured within fruit halves produced proportionately less callus as their fruit diam increased. Juice vesicles cultured in 15–30 mm diam fruits lost their original green color and turned opaque as they matured (i.e., after 3–6 months in culture). A method is also presented, whereby whole lemon fruits can be established and maintained in vitro. Lemons, 35–45 mm in diam, were the best explant sources for establishing whole fruit cultures. Juice vesicles in whole fruit cultures may remain viable for up to 8 months in culture.
LEPIDODENDRON ACULEATUM WITH ATTACHED FOLIAGE: EVIDENCE OF STEM MORPHOLOGY AND FOSSILIZATION PROCESSES
Authors: Leary Richard L. , Thomas Barry A.
Published: January 2018

A 6 m long specimen of Lepidodendron aculeatum Sternberg with attached leaves is described. The preserved portion of this axis gradually tapers from 38 cm wide at the lower end to 33.5 cm at the top. Ligule pit casts are present immediately above the leaf scars; they are similar to those of Lower Carboniferous lycophytes Angarodendron, Eskdalia, Tomiodendron, Ursodendron, and Meyenodendron and the Upper Carboniferous Bothrodendron. No such casts have beeen reported previously from Lepidodendron, although ligule pit cuticles have been prepared from Ulodendron, Lepidodendron, and Lepidophloios. This specimen is also unusual in that leaves are attached to the large stem. The specimen consists of external and internal molds, details of which show that the stem increased in width during burial and compression and prior to fossilization. The width of the specimen does not equal the original diameter of the stem but more closely corresponds to one half the circumference of the axis. This flattened log provides further details of overall Lepidodendron morphology and an insight into fossilization processes.
SPORE MORPHOLOGY AND GENERIC DELIMITATION OF NEW WORLD HEMIONITIS, GYMNOPTERIS, AND BOMMERIA (ADIANTACEAE)
Authors: Ranker Thomas A.
Published: January 2018

I would like to thank Chris Haufler for supplying spores of Bommeria species, technical advice, and valuable comments on the manuscript; Lorraine Hammer for much technical assistance and for providing training on the SEM; the curators of ASU and GH for loaned specimens; and, Alan Smith of UC herbarium for supplying spores of G. tomentosa. I am also grateful to W. H. Wagner, Jr., A. F. Tryon, A. Murray Evans, Steve Brunsfeld, George Diggs, Doug Soltis, Pam Soltis, Genie Trapp, Paul Wolf, and two anonymous reviewers for helpful comments and suggestions on earlier drafts of this paper. This work was supported by NSF Dissertation Improvement Grant BSR‐8514431 and a Pierre Stouse, Jr., Memorial Scholarship awarded by the University of Kansas Endowment Association.

Spores of species of Hemionitis, Gymnopteris, and Bommeria were compared for 1) presence of perispores using the sodium hydroxide assay, 2) surface structure of mature perispores and exospores, and 3) development of superficially similar mature perispores. All taxa were shown to possess perispores and greater morphological variation was detected within and among species than previously reported. On the basis of shared morphological and ontogenetic features, groups of species were identified that crossed presently recognized generic boundaries; hence, the existing trigeneric classification is inadequate to depict natural relationships among these taxa. The results also demonstrate that superficial similarity of mature perispores may not be the best indicator of systematic relationship among species, as similar surface patterns may be derived through different developmental pathways.
VARIATION IN THE ULTRASTRUCTURE OF THE BIFLAGELLATE MOTILE CELLS OF SIX UNICELLULAR GENERA OF THE CHLAMYDOMONADALES AND CHLOROCOCCALES (CHLOROPHYCEAE), WITH EMPHASIS ON THE FLAGELLAR APPARATUS
Authors: Watanabe Shin , Floyd Gary L.
Published: January 2018

The ultrastructural features of the biflagellate motile cells of six different species of the Chlorophyceae, namely Dunaliella lateralis (Polyblepharidaceae, Chlamydomonadales), Chlorococcum hypnosporum, Spongiochloris spongiosa, Protosiphon botryoides (Chlorococcaceae, Chlorococcales), Tetracystis aeria and Pseudotetracystis terrestris (Tetracystidaceae, Chlorococcales), were examined with an emphasis on the flagellar apparatus (FA). They have different vegetative characteristics, such as, being motile or nonmotile, variations in chloroplast morphology, possession of one or more nuclei, and reproductive features such as formation of tetrahedral tetrads, and naked or walled zoospores. Ultrastructural differences amongst reproductive cells of the six species include variations in cell surface structure, basal body to basal body angle, beamlike extensions of the distal fiber, extensive connections of the proximal sheath between basal bodies, two‐membered rootlets, striated microtubule‐associated components, two‐membered rootlet‐nucleus and/or mitochondria connections, X‐membered rootlets, connections of rootlets and basal bodies, rhizoplasts and accessory basal bodies. All six species possess pyrenoids penetrated by thylakoid membranes, and the FA typical of the Chlorophyceae (sensu Mattox and Stewart, 1984). These six species should be divided into two groups. The first includes D. lateralis, C. hypnosporum, and T. aeria, in which accessory basal bodies are present, the basal body to basal body angle is relatively fixed, and a cell wall or surface coat is present. The second group includes Ps. terrestris, S. spongiosa, and Pr. botryoides, in which accessory basal bodies are absent, the basal body to basal body angle is variable and the zoospores are naked.
TEMPORAL COMPETENCE OF EMBRYONIC PINUS PONDEROSA COTYLEDONS TO FORM MULTIPLE BUDS IN VITRO
Authors: Ellis David D. , Bilderback D. E.
Published: January 2018

To investigate temporal changes occurring during tissue maturation and loss of organogenic competence, embryos of Pinus ponderosa Laws, were excised from seed and placed horizontally on medium in sterile culture. On a hormone‐free basal medium, cotyledons differentiated and failed to form multiple buds. When placed on a benzyladenine (BA)‐containing medium, the lower cotyledons in contact with the medium formed multiple buds while those elevated above the medium did not. Cotyledons became incompetent to form buds when embryos were initially placed on basal medium for 2 days before being transferred to the BA‐supplemented medium. In order to initiate buds, cotyledons of newly excised embryos had to be exposed to BA for at least 3 days. Exposure to BA for longer than 7 days did not significantly increase the number of cotyledonary buds. Cotyledons elevated above the BA‐supplemented medium retained organogenic competence to form buds for up to 14 days but did not form buds unless the cotyledons were placed in contact with the medium. The presence of BA is required to retard cotyledon maturation and sustain tissue competence to initiate buds.
XYLEM WATER HOLDING CAPACITY AS A SOURCE OF ERROR IN WATER POTENTIAL ESTIMATES MADE WITH THE PRESSURE CHAMBER AND THERMOCOUPLE PSYCHROMETER
Authors: Hardegree Stuart P.
Published: January 2018

The pressure chamber and the thermocouple psychrometer often provide different values when used to estimate plant water potential. One hypothesis to explain the discrepancy between instruments is that water movement between the xylem and symplast occurs during pressurization in the pressure chamber. Pressure chamber and thermocouple psychrometer measurements of Pinus ponderosa (Laws.) seedling shoots and mature Quercus agrifolia (Nee) shoots showed that the discrepancy is greater for Quercus. It was hypothesized that the xylem water content‐water potential relationship of these species would explain the magnitude of the discrepancy between instruments. The xylem water holding capacity alone, however, does not explain the difference between species. The larger discrepancy in Quercus is likely due to a greater volume of water held in the xylem relative to the volume held in the symplast.
GENETIC SIMILARITY IS HIGH BETWEEN INTERCONTINENTAL DISJUNCT SPECIES OF SENECIO (ASTERACEAE)
Authors: Liston Aaron , Rieseberg Loren H. , Elias Thomas S.
Published: January 2018

Senecio flavus (Decne.) Schultz‐Bip. of the Saharo‐Arabian and Namibian deserts and Senecio mohavensis Gray of the Mojave and Sonoran deserts form a pair of closely related disjunct annual taxa. The two species exhibit slight morphological differences and have different ploidy levels: all North American populations examined are tetraploid, while African and Asian populations are diploid. Senecio flavus comprises two morphologically and geographically distinct subspecies, subsp. flavus and subsp. breviflorus Kadereit. Electrophoretic examination of 13 enzymes revealed that the subsp. breviflorus has two additional isozymes relative to subsp. flavus, and that 5. mohavensis has four additional isozymes relative to subsp. breviflorus. Senecio flavus subsp. breviflorus and S. mohavensis are identical at 20 of the 21 (I = 0.952) remaining homologous loci. This value is much higher than the genetic identity values observed in other taxa with disjunct intercontinental distributions such as members of Agastache, Datisca, Liriodendron, and Styrax. This suggests that the Senecio disjunction may be of recent origin. Senecio flavus subsp. flavus from North Africa and Namibia has lower genetic identity values with S. mohavensis (0.857 and 0.805, respectively), implicating S. flavus subsp. breviflorus as the progenitor of 5. mohavensis. The complete lack of heterozygosity confirms that the plants are highly autogamous, and thus could have attained their disjunct distribution through long distance dispersal.
EFFECTS OF PARENTAL IDENTITIES AND ENVIRONMENT ON COMPONENTS OF CROSSING SUCCESS IN PHLOX DRUMMONDII
Authors: Pittman Karen E. , Levin Donald A.
Published: January 2018

A controlled pollination study, involving a diallel crossing scheme among 15 Phlox drummondii individuals grown under either control, low water or low nutrient conditions, was performed. The results of this research demonstrate that, although plant size and flower number are responsive to the treatments, pollen germination percentage, the survival probability of developing seeds and the weight of mature seeds are buffered against water and nutrient deprivation. However, the identities of male and female parents did have significant effects on pollen germination and seed survival, and female identity had a significant effect on seed weight.
BUMBLE BEE POLLINATION AND FLORAL MORPHOLOGY: FACTORS INFLUENCING POLLEN DISPERSAL IN THE ALPINE SKY PILOT, POLEMONIUM VISCOSUM (POLEMONIACEAE)
Authors: Galen Candace , Stanton Maureen L.
Published: January 2018

Pollen dispersal success in entomophilous plants is influenced by the amount of pollen produced per flower, the fraction of pollen that is exported to other flowers during a pollinator visit, visitation frequency, and the complementarity between pollen donor and recipients. For bumble bee‐pollinated Polemonium viscosum the first three determinants of male function are correlated with morphometric floral traits. Pollen production is positively related to corolla and style length, whereas pollen removal per visit by bumble bee pollinators is a positive function of corolla flare. Larger‐flowered plants receive more bumble bee visits than small‐flowered individuals. We found no evidence of tradeoffs between pollen export efficiency and per visit accumulation of outcross pollen; each was influenced by unique aspects of flower morphology. Individual queen bumble bees of the principal pollinator species, Bombus kirbyellus, were similar in male, female, and absolute measures of pollination effectiveness. An estimated 2.9% of the pollen that bumble bees removed from flowers during a foraging bout was, on average, deposited on stigmas of compatible recipients. Significant plant‐to‐plant differences in pollen production, pollen export per visit, and outcross pollen receipt were found for co‐occurring individuals of P. viscosum indicating that variation in these fitness related traits can be seen by pollinator‐mediated selection.
EFFECTS OF PLANT MORPHOLOGY AND EMERGENCE TIME ON SIZE HIERARCHY FORMATION IN EXPERIMENTAL POPULATIONS OF TWO VARIETIES OF CULTIVATED PEAS (PISUM SATIVUM)
Authors: Ellison Aaron M. , Rabinowitz Deborah
Published: January 2018

The effects of plant form and emergence time on size hierarchy formation in populations of two morphologically and genetically distinct varieties of peas (leafless and leafed) were studied. There were no significant differences in germinability between the two varieties, although leafless peas imbibed more rapidly than the leafed ones did. Monocultures of leafed and leafless peas were established at two densities: plants grown alone in small pots and plants grown at 576 m ‐. Time emergence was noted, and plant shape, biomass and seed production were measured at two‐week intervals for ten weeks. Seedlings emerged continually over an eight‐day period, and two cohorts of seedlings were distinguished (seedlings emerging 6–7 days after planting, and seedlings emerging > 7 days after planting). Dominance and suppression were observed in the high‐density populations, and early‐emerging plants had less hierarchical biomass distributions than did late‐emerging ones. Although leafless peas were larger and suffered less mortality than leafed ones did at identical densities, there were no differences in the degree of size inequality between the two genotypes (emergence cohorts pooled), or within emergence cohorts between genotypes. The degree of size inequality increased with time among dominant individuals and decreased with time among suppressed individuals. These results broadly support Weiner and Thomas's (1986) hypothesis that plant form may affect the extent but not the existence of competitive asymmetry in plant populations.
ADAPTIVE RELATIONSHIP BETWEEN LEAF WATER REPELLENCY, STOMATAL DISTRIBUTION, AND GAS EXCHANGE
Authors: Smith W. K. , McClean T. M.
Published: January 2018

Although numerous studies have considered the functional significance of the terrestrial plant leaf surface, the importance of water repulsion for enhancing photosynthetic carbon uptake (CO2) has not been recognized and appears to involve an array of structural adaptations. The large majority of species tested had leaf surfaces that repelled water to such an extent that varying degrees of water‐bead formation occurred. On more wettable leaves, the formation of a water surface film (dewfall) severely curtailed photosynthetic CO, uptake in the field, most likely because CO2 diffuses 104 times slower in water than air. Water bead formation not only enabled maintenance of high photosynthetic rates but also increased water use efficiency several fold. In 3 of 5 species tested in the field, water bead formation after artificial wetting resulted in greater stomatal opening and increases in photosynthesis of up to 34%. The most nonwettable leaf surface on a given leaf also had all or the majority of the leaf's stomata in 50 of the 57 species tested, indicating a potentially strong adaptive relationship between leaf surface wettability, stomatal occurrence, and photosynthetic performance.
SUPERNUMERARY CHROMOSOMES IN TRADESCANTIA II. EFFECT OF COLCHICINE ON MEIOTIC ISOCHROMOSOME CONFIGURATIONS
Authors: Hauber Donald P. , Rovira Klar A.
Published: January 2018

The effect of colchicine on meiotic pairing and configuration frequencies of three homologous isosupernumerary chromosomes was investigated. In the absence of colchicine, the three isochromosomes displayed a high degree of interchromosomal pairing and chiasma formation. As a consequence, a high frequency of bivalents and trivalents were observed at diakinesis‐metaphase I. The unique structure of isochromosomes enables them to pair intrachromosomally (i.e., foldback pairing) yet the preferential occurrence of interchromosomal pairing suggests that all six arms of the three isosupernumerary chromosomes were in close association prior to or upon initiation of synapsis. Supernumerary chromosomes in microsporocytes treated during presynapsis or early synapsis with colchicine exhibited a significant reduction (P < 0.001) in the number of bivalents and trivalents at diakinesis. However, there was no reduction in overall chiasma frequency among supernumeraries due to the induction of increased intrachromosomal pairing and chiasma formation. A colchicine‐sensitive association or alignment of homologues preceding effective pairing has been demonstrated in standard chromosomes of a number of plant species. This study provides the first evidence to indicate that at least certain supernumerary chromosomes may display presynaptic association as well. The results also support the strongly held contention that colchicine is not directly preventing or inhibiting the actual formation of chiasmata, since no reduction in chiasma frequency was observed in the isochromosomes.
MORPHOGRAM: A NOVEL DIAGRAM TO ORGANIZE THE TRANSITIVE SECONDARY XYLEM ELEMENTS OF BASAL TOMATO (SOLANUM LYCOPERSICUM) INTERNODES
Authors: van der Schoot Chris , van Bel Aart J. E.
Published: January 2018

In the internodal secondary xylem of tomato (Solanum lycopersicum L. cv. Moneymaker) there are five main groups of secondary xylem elements which can be distinguished in wood macerates of basal internodes of the plant. Their top‐frequency lengths are distinct: ray parenchyma cells (80 μm); fusiform parenchyma cells and strands (250 μm); vessel members (290 μm); tracheids (350 μm); and fibrous elements (590 μm), although there is overlap in length and morphology. The imperforate axial elements are strikingly diverse and morphologically intergrading, precluding ready classification according to traditional wood anatomical standards. In a novel, more appropriate, flexible categorization the variability in imperforate axial elements is depicted in a morphogram in which pit shape is plotted against cell length and cell morphology. This morphogram organizes the various elements without imposing an absolute classification. It is concluded that the appreciable variation in tomato wood samples results from developmental plasticity. The morphogram elucidates the extent and nature of element variation at the morphological level. Thus, it can be used to record developmental plasticity of wood tissues to assess interplant variation in wood tissue development, as well as intraplant plasticity.
NEIGHBOR EFFECTS IN MAST YEAR SEEDLINGS OF ACER SACCHARUM
Authors: Taylor Kimberly M. , Aarssen L. W.
Published: January 2018

The size and age distributions of Acer saccharum Marsh, seedlings were studied in a mature hardwood forest in southeastern Ontario between 26 June and 26 September 1986. Ninety‐one percent of the seedlings surveyed were produced in 1984 which was a mast year for this population of sugar maple. Mean height within quadrats was negatively correlated with the density of two‐year‐old seedlings in the first half of the sampling period, suggesting that competition may be an important factor affecting seedling size. A significant positive correlation in the second half of the sampling period, however, suggested a temporal shift in the pattern of seedling growth in which the shorter, more suppressed seedlings under the higher densities had increased their relative height in response to earlier competition. The sum of the heights of pairs of nearest neighboring seedlings sampled over the survey period was negatively correlated with the distance between them. The sum of the biomasses of pairs of nearest neighboring seedlings collected in October 1986, however, was positively correlated with the distance between them. Variation in the height of two‐year‐old seedlings was unaffected by light intensity but was to some extent accounted for by soil variables, and total percent cover of other species. The density of the two‐year‐old seedlings, however, accounted for the largest percentage of the variation in their mean height. The data suggest that competition between the seedlings derived from mast seeding in 1984 may represent an important component of the process of natural selection affecting this population.
EFFICACY OF EXPLOSIVE VS. HYGROSCOPIC SEED DISPERSAL BY AN ANNUAL GRASSLAND SPECIES
Authors: Stamp Nancy E.
Published: January 2018

Seeds of Erodium moschatum (Geraniaceae) were moved on average 56 cm by primary, explosive dispersal and then traveled another 7 cm across the soil surface through activity of the hygroscopic awn, although not necessarily away from the source. In a 10‐day field experiment, 68% of the diaspores buried themselves through activity of the awn. The percentage of seeds becoming buried per day was not correlated with rainfall. More seeds became buried on plant‐littered ground, with litter cover from 8 to 61%, than on bare soil. As soil compaction increased, burial on littered surfaces declined. In laboratory experiments using straw to simulate sparse densities of plant litter, the percent of burial was enhanced, but sticks simulating plant stems did not facilitate burial. In a greenhouse experiment, more buried seeds germinated than unburied seeds. Buried seeds produced seedlings that developed more quickly, had higher survivorship and had greater shoot biomass than those from unburied seeds. Self‐burial also ensured that the radicle was positioned downward, which probably contributed to the observed higher survivorship. Overall, in semiarid grasslands, plant‐littered microhabitats are probably more favorable sites for the placement of seeds than bare areas (e.g., compacted gopher mounds). Littered sites promote self‐burial and burial promotes seedling establishment, survival and growth.
POLLEN TUBE ATTRITION IN ERYTHRONIUM GRANDIFLORUM
Authors: Cruzan Mitchell B.
Published: January 2018

Seed set after selfing in E. grandiflorum is often reduced relative to seed set after crossing; however, the compatibility patterns seen are not due to genes of major effect (i.e., S alleles). There is quantitative variation in the proportion of pollen tubes reaching the base of the style after both self‐ and cross‐pollinations. Pollen tubes require between 24 and 72 hr to reach the ovary, but pollen tube growth ceases after 72 hr. When styles were removed from the ovaries 5 days after pollination, between 10 and 80% of the pollen tubes in the stigma had not reached the base of the style. The number of pollen tubes at the base of the style is a much better predictor of seed set than is the number of pollen tubes in the stigma. Pollen tube attrition is not affected by the age of the recipient flower or by the number of pollen donors contributing to the stigmatic pollen pool. The number of pollen tubes reaching the base of the style is dependent upon the source of the pollen and appears to be a decelerating function of the number of pollen tubes present in the stigma.
AN UNUSUAL ANIMAL‐PLANT INTERACTION: FEEDING OF SCHOMBURGKIA TIBICINIS (ORCHIDACEAE) BY ANTS
Authors: Rico‐Gray Victor , Barber John T. , Thien Leonard B. , Ellgaard Erik G. , Toney Jeffrey J.
Published: January 2018

The hollow pseudobulbs of Schomburgkia tibicinis (Orchidaceae; Central America) serve as domatia for many species of ants. The ants pack many of the pseudobulbs with debris including dead insects, plant material, and sand. Ants were fed 14C‐labelled D‐glucose in honey, killed, and placed in the pseudobulbs for up to eight weeks. Samples of plant tissue were harvested and tested for radioactivity after 1, 2, 3, 4, 6, and 8 weeks. The labelled material had moved into various parts of the plant and demonstrated direct nutrient uptake.