bluuebunny/crossref_metadata_2025 huggingface dataset:
DEVELOPMENT AND EVOLUTION OF BASAL CAULINE PLACENTATION: BASELLA RUBRA
Authors: Sattler Rolf , Lacroix Christian
Published: January 2018

In Angiosperms placentae or ovules are formed on carpels or the floral apex. Hence, in a developmental sense, there are carpellate and acarpellate gynoecia. The latter occur in about 11% of all Angiosperm families.Basella rubrais an example of the noncarpellate condition. Its single basal ovule is formed directly from the floral apex. In young developmental stages it even retains the tunica‐corpus organization of the floral apex. In later developmental stages, three septa arise only at the base of the ovule. The single vascular strand of the ovule is symmetrically derived from the bases of all six strands that supply the ovary wall, i.e., it is not associated with the vascular strand of only one of the three gynoecial appendages. Hence, neither development nor vascularization support a carpellate interpretation of theBasellagynoecium. With regard to the evolution of basal placentation inBasellaand other taxa of Angiosperms three possibilities exist: 1) It is derived from the carpellate condition, 2) It is primitive and the carpellate condition is derived, 3) Both carpellate and noncarpellate organizations have coexisted during the evolution of Angiosperms which may have been monophyletic or polyphyletic.
GEITONOGAMOUS POLLINATION AND ITS CONSEQUENCES IN GERANIUM CAESPITOSUM
Authors: Hessing Mark B.
Published: January 2018

In many plants, the frequency of geitonogamous (within‐plant) pollination is likely to increase as a function of the number of simultaneously blooming flowers. This increase in self‐pollination often produces inbreeding depression. Thus, a dilemma may exist in that individuals cannot increase seed production without lowering the average fitness of each seed. Conditions necessary for the existence of the dilemma were confirmed in large individuals of the herbaceous perennial Geranium caespitosum. Manually geitonogamously pollinated flowers initiated as many fruits as manually outcrossed flowers, but showed a subsequently greater number of embryo abortions, matured fewer seeds, and had a lower average seed weight. Observations of pollinators and dye transfer showed that geitonogamous bee pollinations increased as the number of flowers per plant increased. A simple model predicted that detrimental effects from geitonogamy become likely when 55 flowers are simultaneously blooming. Plants with 55 or more flowers produced 30% of the flowers in populations. The effect, and possible circumvention, of the dilemma on Geranium, and angiosperm breeding systems in general, is discussed.
REPRODUCTIVE SUCCESS AND INFLORESCENCE SIZE OF CALOPOGON TUBEROSUS (ORCHIDACEAE)
Authors: Firmage David H. , Cole F. Russell
Published: January 2018

Reproductive success of Calopogon tuberosus, which produces no nectar, was investigated in relation to inflorescence size and dispersion pattern. Mean inflorescence size was 2.56 (range 1–10). A bagging experiment showed that insects are required for pollen transfer and that fruits are produced from self‐, geitonogamous, and cross‐pollinations; fruit set was not 100%. Fruit set of nonmanipulated plants was limited by the number of pollinator visits. Reproductive success increased with increasing inflorescence size, although not above theoretical predictions. However, the probability of producing no fruit or contributing no pollinia decreased with increasing inflorescence size since sequential flowering increased the probability of a pollinator visit to the inflorescence over the blooming period. Large inflorescences did not provide a greater pollinator attraction than small ones, because inflorescences only presented a few open flowers at a time. In addition, flowers on plants growing in clumps of 2–8 plants had a higher probability of setting fruit, apparently because of increased pollinator attraction. Although there are obvious selective advantages for large inflorescences, the sequential flowering habit, and low resource availability may reduce the advantages of large inflorescence size at our study site.
A NEW TAXODIACEOUS SEED CONE FROM THE OLIGOCENE OF WASHINGTON
Authors: Miller Charles N. , Crabtree David R.
Published: January 2018

Cunninghamiostrobus goedertii is described as a new species based on permineralized seed cones from the Early Oligocene of Washington. The fossils come from the Makah Formation and were found on the northern shore of the Olympic Peninsula. The cone consists of numerous bract‐scale complexes arranged helically around a central axis. Each bract‐scale complex has a large bract bearing a small flap of tissue adaxially that represents the ovuliferous scale. Up to three seeds were produced on each complex. The vascular trace to the bract‐scale complex diverges from the vascular cylinder of the cone axis as a concentric strand. This divides in the outer cortex of the axis to form a large collateral bract tract abaxially and a minute scale trace adaxially. The latter continues outward to supply the ovuliferous scale. The bract trace divides, forming many strands outward which occur in a row with transfusion tissue between them. Many resin canals also occur in the bract. The new cone combines features found in modern cones of Athrolaxis, Cunninghamia, and Taiwania but is most similar to Cunninghamiostrobus yubariensis from the Late Cretaceous of Japan.
ATTACHED REPRODUCTIVE AND VEGETATIVE REMAINS OF THE EXTINCT AMERICAN‐EUROPEAN GENUS CEDRELOSPERMUM (ULMACEAE) FROM THE EARLY TERTIARY OF UTAH AND COLORADO
Authors: Manchester Steven R.
Published: January 2018

Fossil twigs with attached foliage, fruits, and flowers from the middle Eocene of the Green River Formation in northeastern Utah and northwestern Colorado and from the early Oligocene Florissant beds of central Colorado provide a firm basis for reconstructing two species of an extinct ulmaceous genus that was widely distributed in the Tertiary of midlatitude western North America and Europe. The fruits are samaras of Cedrelospermum Saporta, a genus previously known only from isolated specimens. The distichously arranged, slender, pinnate‐veined leaves vary from serrate with simple teeth to, less commonly, entire‐margined. Corresponding isolated leaves in the Green River, Florissant, and other Eocene to Oligocene localities of western North America are now excluded from Zelkova and Myrica, to which they were previously misidentified. The anthers of the staminate flowers contain 3–5 porate pollen with rugulate sculpture. Based upon combined characters of phyllotaxy, and leaf, flower, fruit, and pollen morphology, Cedrelospermum can be referred to the extant subfamily Ulmoideae, and is similar to Phyllostylon, Zelkova, and Hemiptelea. The abundance of Cedrelospermum in lake sediments of volcanic areas, together with its production of numerous small winged fruits, suggest that it was an early successional colonizer of open habitats.
ADVENTIVE ORGANOGENESIS FROM SOMATIC TISSUE CULTURES OF SOLANUM CAROLINENSE: ORIGIN AND DEVELOPMENT OF REGENERATED PLANTS
Authors: Reynolds Thomas L.
Published: January 2018

The development of adventitious shoot formation from cultured somatic tissues of Solanum carolinense was studied using light microscopy. For purposes of comparison, callus initiation and proliferation were also followed. When stem segments of this plant were cultured on medium supplemented with 6 mg/l benzyladenine (BA), cell division was first observed after 48 hr in the external phloem and inner cortex of the segments. This division activity gave rise to meristematic zones which subsequently formed shoot primordia within 6 days of culture. While organogenic potential appears to be limited to specific regions, all tissues of the explant were capable of callus formation when cultured on medium containing 3 mg/l 2,4‐dichlorophenoxyacetic acid (2,4‐D). In conjunction with a previous study, it appears that unlike somatic embryogenesis in this species, organogenesis does not require an intermediate callus phase for differentiation to occur.
ASPECTS OF CONE AND OVULE ONTOGENY IN CRYPTOMERIA (TAXODIACEAE)
Authors: Takaso T. , Tomlinson P. B.
Published: January 2018

The axillary complex of female cones of Cryptomeria is initiated as a tangentially extended triangular structure with a rounded apex. It is bilaterally symmetrical. Structures interpreted as prophylls are differentiated first, but they become insignificant in later development. They are succeeded by two successive pairs of lobes, each lobe being the common primordium for an adaxial ovule and a tooth. The ovule initially much exceeds the tooth. The apex of the complex has a diversity of fates and may differentiate as an ovule‐tooth pair. A one‐to‐one relation between teeth and ovules may be lost by abortion of ovules. The initial relation between teeth and ovules is obscured in later development due to extension of tissues at the base of the complex associated with considerable enlargement of the teeth. Histogenesis of the various parts is described, together with the vascular system. There is a vascular supply to the tooth but not the ovule. The results support a direct comparison with the extinct transition conifers Pseudovoltzia and Aethophyllum but do not fully support Florin's generalized model for the arrangement of parts in the axillary complex of conifers.
INFLORESCENCE SIZE: TEST OF THE MALE FUNCTION HYPOTHESIS
Authors: Campbell Diane R.
Published: January 2018

One explanation for low fruit sets in plants with hermaphroditic flowers is that total flower production by a plant is controlled primarily by selection through male function. This male function hypothesis presupposes that success in pollen donation increases more strongly with flower number than does seed set. I tested this prediction by measuring male and female components of reproductive success as functions of flower number in natural populations of the self‐incompatible, perfect flowered plant, Ipomopsis aggregata. Fruit set in this hummingbird‐pollinated plant averaged 4.9 to 40.3% across the 4 years of study. Both the total amount of pollen donated and the total amount received, as estimated by movement of fluorescent powdered dyes, increased linearly with number of flowers on a plant. Total seed production, however, increased disproportionately quickly because plants with larger floral displays were more likely to set at least one fruit. An estimate of the functional femaleness of a plant, based on pollen donation and seed production, increased with flower number. These results do not support the male function hypothesis.
WATER SHARING AMONG RAMETS IN A DESERT POPULATION OF DISTICHLIS SPICATA (POACEAE)
Authors: Alpert Peter
Published: January 2018

Clonal growth enables plants to transport resources among separately rooted but connected ramets, a potential advantage in patchy or unpredictable habitats. Nevertheless, clonal plants are relatively scarce in deserts. To test whether clonal integration of water relations can increase plant performance under natural conditions in a desert species, water movement was traced and connection among ramets was manipulated in the rhizomatous grassDistichlis spicatain Death Valley, California. To examine potential costs of clonal growth form, connections were mapped and analyzed for dry mass and nitrogen content. Movement of dye showed potential transport of water among five ramets up to 1.4 m apart. Severance of connecting rhizomes increased mortality and decreased water potential of individual ramets within 36 hr, indicating that water sharing among ramets could be of significant benefit. However, plants had a high investment of mass and nitrogen in underground organs, which might be a cost of clonal growth associated with desert environments.
ENVIRONMENTAL AND PHYSIOLOGICAL FACTORS INFLUENCING THE NATURAL DISTRIBUTION OF EVERGREEN AND DECIDUOUS ERICACEOUS SHRUBS ON NORTHEAST AND SOUTHWEST SLOPES OF THE SOUTHERN APPALACHIAN MOUNTAINS. I. IRRADIANCE TOLERANCE
Authors: Lipscomb M. V. , Nilsen E. T.
Published: January 2018

Deciduous and evergreen species are segregated on northeast and southwest slopes of the southern Appalachian Mountains. The segregated distributions of three ericaceous shrubs (Rhododendron maximum valley positions; Rhododendron periclymenoides on northeast slopes; Kalmia latifolia on southwest slopes) were compared to the respective irradiance environments. Growth patterns of field plants, and photosynthetic acclimation of each species to three irradiance treatments in a phytotron were studied. Rhododendron maximum, an evergreen species, was found to be most sensitive to high radiation. In phytotron experiments, quantum yield, light saturated photosynthetic capacity, photosynthesis per chlorophyll, and water use efficiency decreased at high ambient irradiance for R. maximum. These characteristics limit the growth of R. maximum on high irradiance southwestern slopes. Both K. latifolia and R. periclymenoides were able to improve their photosynthetic performance at high ambient irradiance. Rhododendron periclymenoides, a deciduous species, was found to continue increasing leaf conductance at high irradiance without an increase in photosynthesis indicating a possible limitation by water in high light environments such as southwest slopes. Kalmia latifolia, an evergreen species, had reduced photosynthetic capacity and reduced water use efficiency when grown in low irradiance conditions which coincides with the higher K. latifolia abundance on high light, southwestern slopes.
THE INFLUENCE OF WATER STRESS ON STEM AND LEAF PHOTOSYNTHESIS IN GLYCINE MAX AND SPARTEUM JUNCEUM (LEGUMINOSAE)
Authors: Nilsen Erik T. , Bao Yijia
Published: January 2018

Stem and leaf photosynthesis were measured in Glycine max var. essex (soybean) and Sparteum junceum (Spanish broom). The significance of stem photosynthesis to whole plant growth was evaluated by blocking stem photosynthesis with black straw sections. The growth of S. junceum was reduced by 18% when black straws were used in comparison to clear straws. The whole plant growth of G. max was not influenced by blocking the stem carbon contribution. Mean midday leaf photosynthesis was 12 μmol CO2 m–2 s–1 and 17 μmol CO2 m–2 s–1 for G. max and 5. junceum, respectively. Mean midday stem photosynthesis of S. junceum was 6.5 μmol CO2 m–2 s–1; however, positive net photosynthesis did not occur in G. max stems. Water stress caused a proportionally greater decrease in leaf photosynthesis compared to that of stems during diurnal cycles of photosynthesis in S. junceum. As a result the contribution to canopy carbon gain by stem photosynthesis increased from 38% to 48% of the total plant carbon gain under reduced water availability.
EFFECTS OF ULTRAVIOLET‐B RADIATION ON FUNGAL DISEASE DEVELOPMENT IN CUCUMIS SATIVUS
Authors: Orth Ann B. , Teramura Alan H. , Sisler Hugh D.
Published: January 2018

Three cucumber (Cucumis sativus L.) cultivars were exposed to a daily dose of 11.6 kJ m‐2biologically effective ultraviolet‐B (UV‐BBe) radiation in an unshaded greenhouse before and/ or after infection by Colletotrichum lagenarium (Pass.) Ell. and Halst. or Cladosporium cucumerinum Ell. and Arth. and analyzed for disease development. Two of these cultivars, Poinsette and Calypso Hybrid, were disease resistant, while the third cultivar, Straight‐8, was disease susceptible. Preinfectional treatment of 1 to 7 days with UV‐BBE in Straight‐8 led to greater severity of both diseases. Postinfectional UV treatment did not lead to increased disease severity caused by C. lagenarium, while preinfectional UV treatment in both Straight‐8 and Poinsette substantially increased disease severity. Although resistant cultivars Poinsette and Calypso Hybrid showed increased anthracnose disease severity when exposed to UV‐B, this effect was apparent only on the cotyledons. Both higher spore concentration and exposure to UV‐B radiation resulted in greater disease severity. Of the cucumber cultivars tested for UV‐B sensitivity, growth in Poinsette was most sensitive and Calypso Hybrid was least sensitive. These preliminary results indicate that the effects of UV‐B radiation on disease development in cucumber vary depending on cultivar, timing and duration of UV‐B exposure, inoculation level, and plant age.
GENETIC STABILITY OF ANTHER CALLUS LINES AND PROGENY PLANTS OF MAIZE
Authors: Ting Y. C. , Gu M. G.
Published: January 2018

Cytological observations showed that mitotic variations among the four callus lines were toward different directions; two to haploidy, one to diploidy, and the fourth to polyploidy. These differences might be caused by varying genetic backgrounds. Under appropriate conditions, certain regenerable callus lines could be maintained by continued subcultures for an indefinite period of time. Microscopic examinations revealed that meiotic chromosome fusion in maize anther culture‐derived R0 plants were again found in the R1 and R2 plants. This suggests that a genetic mechanism was involved in bringing about this characteristic fusion. This mechanism probably arose de novo during culturing since no fusion was found in the parental lines. Through a rigid selection for healthy and vigorous plants for two to three generations, genetically stable inbred lines originating from maize anther culture have been established.
ANATOMICAL STUDIES ON FIRST‐YEAR WINTER INJURED RED SPRUCE FOLIAGE
Authors: Adams Gregory T. , Perkins Timothy D. , Klein Richard M.
Published: January 2018

Foliar injury to red spruce (Picea rubens Sarg.) occurred during the winter of 1989–1990. A range of damage was observed among individual trees, first‐year needles on a shoot, and often within an individual needle. Anatomical comparisons of first‐year foliage were made to establish patterns of necrosis due to winter injury. Mesophyll tissue was most affected by winter damage. Guard cells adjacent to injured mesophyll cells were also consistently damaged. Early evidence of injury was apparent as an off‐color staining of the cytoplasm and slight plasmolysis of the protoplast. Organelle integrity was lost, and there was an extensive reduction of cytoplasmic volume. Spherical bodies of unidentified composition often appeared within the cytoplasm as subcellular integrity was lost. Severe damage resulted in complete loss of cellular structural integrity and adhesion of residual cellular contents to the cell walls. Narrow transition zones between healthy and necrotic tissues were observed, and upper surfaces tended to be more severely affected. There appeared to be a cellular specificity to winter injury within the mesophyll. Completely necrotic cells were often adjacent to apparently healthy cells, and a wide range of injury could be observed within a relatively small area of the needle in partially damaged foliage.
A NEW SPECIES AND NEW SECTIONS OF RHIPIDOCLADUM (POACEAE: BAMBUSOIDEAE)
Authors: Clark Lynn , Londoño Ximena
Published: January 2018

Rhipidocladum longispiculatum, a woody bamboo from the montane forests of Colombia, is described and illustrated. A classification of Rhipidocladum into three sections is proposed based on differences in internode structure, culm leaves, fimbriae of the foliage leaf sheaths, inflorescences, spikelet bracts, and foliar anatomy and micromorphology. Rhipidocladum section Rhipidocladum is distinguished by the zigzag rachis of the inflorescence and obtuse spikelet bracts, and includes only one species, R. harmonicum. Section Didymogonyx is characterized by alternating long and short internodes, and includes R. longispiculatum and R. geminatum. Section Racemiflorum is distinguished by its relatively long culm leaf blades, racemiform inflorescences, and mucronate or aristate spikelet bracts; the remainder of the species of the genus are classified within this section. A review of morphology, foliar anatomy, and micromorphology of the Arthrostylidiinae, the subtribe to which Rhipidocladum belongs, is presented. The problem of generic classification within the subtribe is discussed with respect to its mosaic pattern of morphological and anatomical variation.
FLOODWATER TEMPERATURE AND STEM LENTICEL HYPERTROPHY IN MANGIFERA INDICA (ANACARDIACEAE)
Authors: Larson Kirk D. , Davies Frederick S. , Schaffer Bruce
Published: January 2018

One‐year‐old seedling trees of Mangifera indica L. cv. Peach were exposed to floodwater temperatures of 15, 22.5, or 30 C for at least 13 days. Immediately prior to flooding, and at daily intervals thereafter, trees were visually examined for evidence of lenticel hypertrophy. Although lenticel hypertrophy was first apparent after 5 days of submergence at 30 C, and after 6 days at 22.5 C, the mean number of days of flooding until lenticel hypertrophy was first observed was 6.6 and 8.1 for the 30 and 22.5 C treatments, respectively. Even after 28 days, lenticel hypertrophy did not occur on plants flooded at 15 C. Initial stages of lenticel hypertrophy were characterized by development of intercellular spaces in the phellem and production of additional phellem tissue by increased phellogen activity. Later stages of hypertrophy were characterized by development of intercellular spaces in the phellem and cortex. Tree survival was not affected by floodwater temperature or lenticel hypertrophy.
ORGAN INITIATION AND DEVELOPMENT OF INFLORESCENCES AND FLOWERS OF ACACIA BAILEYANA
Authors: Derstine Kittie S. , Tucker Shirley C.
Published: January 2018

Inflorescence and floral ontogeny are described in the mimosoid Acacia baileyana F. Muell., using scanning electron microscopy and light microscopy. The panicle includes first‐order and second‐order inflorescences. The first‐order inflorescence meristem produces first‐order bracts in acropetal order; these bracts each subtend a second‐order inflorescence meristem, commonly called a head. Each second‐order inflorescence meristem initiates an acropetally sequential series of second‐order bracts. After all bracts are formed, their subtended floral meristems are initiated synchronously. The sepals and petals of the radially symmetrical flowers are arranged in alternating pentamerous whorls. There are 30–40 stamens and a unicarpellate gynoecium. In most flowers, the sepals are initiated helically, with the first‐formed sepal varying in position. Petal primordia are initiated simultaneously, alternate to the sepals. Three to five individual stamen primordia are initiated in each of five altemipetalous sectorial clusters. Additional stamen primordia are initiated between adjacent clusters, followed by other stamens initiated basipetally as well as centripetally. The apical configuration shifts from a tunica‐corpus cellular arrangement before organogenesis to a mantle‐core arrangement at sepal initiation. All floral organs are initiated by periclinal divisions of the subsurface mantle cells. The receptacle expands radially by numerous anticlinal divisions in the mantle at the summit, concurrently with proliferation of stamen primordia. The carpel primordium develops in terminal position by conversion of the floral apex.
PATTERN, TEMPO, AND MODE OF EVOLUTIONARY AND BIOGEOGRAPHIC DIVERGENCE IN OXYSTYLIS AND WISLIZENIA (CAPPARACEAE)
Authors: Vanderpool Staria S. , Elisens Wayne J. , Estes James R.
Published: January 2018

Six populations of Oxystylis lutea and nine populations representing three subspecies of Wislizenia refracta were analyzed for electrophoretic variation at 18 loci. Several marker alleles differentiate O. lutea from W. refracta, although mean pair‐wise genetic identity values (range, 0.53–0.64) are comparable to those found among many congeners. Oxystylis and Wislizenia share two duplicated gene loci that are not present in outgroup species in Cleome and Cleomella. Thus, they appear to be monophyletic sister taxa within a larger monophyletic group. Based on allozyme differentiation patterns, we infer a pre‐Pleistocene divergence prior to differentiation within W. refracta. Subsequent anagenesis in the O. lutea lineage and cladogenesis in the W. refracta lineage have resulted in extensive morphological differentiation between Oxystylis and Wislizenia. Therefore, Oxystylis and Wislizenia are phenetically and phylogenetically distinct, and we recognize them as genera. Geographic modes of speciation predominate in the group. Variation patterns within W. refracta are consistent with recognition of three subspecies, and indicate that subsp. californica is not a historical introduction in the Central Valley of California.
THE INTRAFLORAL PHENOLOGY OF STREPTANTHUS TORTUOSUS (BRASSICACEAE)
Authors: Preston Robert E.
Published: January 2018

The sequence of floral events during anthesis was examined in Streptanthus tortuosus to determine the relationship between the male and female floral phases. The flowers are strongly protandrous. In the staminate phase, the anthers mature sequentially over a 3–4‐day period. Because pollinators quickly remove pollen from the anthers, sequential anther maturation prolongs the male phase relative to what it would be if anthers did not mature sequentially. Pollen applied to the stigma during the staminate phase does not adhere readily and does not germinate. The length of the pistillate phase depends on pollinator activity, as pollination accelerates the abscission of floral parts. Unpollinated flowers remain pistillate for 3–4 days, during which time stigmatic receptivity declines gradually. In the field, 72% to 80% of flowers are staminate at any time, indicating that the staminate phase is three times longer than the pistillate phase when pollinators have access to the flowers. The consequences of the relative length of the floral phases and the schedule of stigmatic receptivity are discussed in terms of outcrossing mechanism, floral longevity, and sexual selection models.
POLLEN‐PISTIL INTERACTIONS IN TRISTYLOUS PONTEDERIA SAGITTATA (PONTEDERIACEAE). II. PATTERNS OF POLLEN TUBE GROWTH
Authors: Scribailo Robin W. , Barrett Spencer C. H.
Published: January 2018

Pollen tube behavior was compared after legitimate and illegitimate pollinations of tristylous Pontederia sagittata. All pollinations resulted in substantially fewer pollen tubes in the style than pollen grains on the stigma surface. Number of pollen tubes showed a characteristic attrition, particularly by the midpoint of the style in all pollination types. Two classes of illegitimate pollination could be identified. In pollinations with pollen smaller than the legitimate size class for a given morph, pollen tubes ceased growth in characteristic regions of the style. In pollinations with pollen larger than the legitimate size class, pollen tubes entered the ovary. In the latter class of pollination, pollen tube behavior in the M morph was similar to that of legitimate pollinations. In the S morph illegitimate pollen tube behavior was distinctive. Pollen tubes entered the ovary but rarely contacted the obturator most often growing down the funiculus of the ovule and terminating growth at its base. The associations between pollen size, pollen tube length and width, and callose plug length regardless of pollination type suggest that incompatibility in P. sagittata is governed by the interaction of heteromorphic characters rather than by an active rejection mechanism mediated by molecular specificities. The distinctive features of incompatibility in P. sagittata are discussed in relation to structural features of the pollen tube pathway, incongruity mechanisms, and gametophytic incompatibility in monocotyledonous families.
PHOTOSYNTHETIC CHARACTERISTICS AND POTENTIAL MOISTURE STRESS FOR THE ACTINORHIZAL SHRUB, MYRICA CERIFERA (MYRICACEAE), ON A VIRGINIA BARRIER ISLAND
Authors: Young Donald R.
Published: January 2018

Seasonal variations in photosynthesis and water relations parameters were quantified for Myrica cerifera, the dominant woody species on the barrier islands along the eastern shore of Virginia. From June through September of 1989, maximum values were 35 μmol m−‐2 sec−‐1 for net CO2 assimilation, 10.5 mm sec−‐1 for stomatal conductance to water vapor diffusion, and –0.3 MPa for xylem pressure potential at the field site on Hog Island. Midday minimum xylem pressure potential often was less than –1.5 MPa. Data from the field and measurements on glasshouse plants indicated that stomatal opening and photosynthesis were sensitive to leaf water potential (<–0.8 MPa) and the leaf‐to‐air humidity deficit (>1.5 kPa). Using meteorological data and derived photosynthetic responses, predictions indicated that M. cerifera photosynthesis would have been limited at the field site due to nonoptimal air temperatures and humidity deficits on at least 90% of the days during the relatively wet summer of 1989. By comparison, these parameters were expected to limit photosynthesis on all but 2 d, or more than 98% of the time during the relatively dry summer of 1990. The sensitivity of Myrica cerifera to atmospheric humidity and plant moisture status may explain the distributional preference for the more mesic swale sites of barrier islands.
GRAVITY‐INDUCED EFFECTS ON MATERIAL PROPERTIES AND SIZE OF LEAVES ON HORIZONTAL SHOOTS OF ACER SACCHARUM (ACERACEAE)
Authors: Niklas Karl J.
Published: January 2018

The influence of gravity on the size and mechanical properties of mature leaves on horizontal shoots and etiolated seedlings of Acer saccharum Marsh. (Aceraceae) was examined. Leaves were grouped into three categories regarding their location on shoots (dorsal or “top” T, lateral or “left/right” L/R, and ventral or “bottom” B). Young's modulus E, petiole length L, lamina surface area A and weight P, and the cross‐sectional areas of different tissues within petioles were measured for each leaf and were found to be correlated with leaf location (T, L/R, and B): T leaves were smaller and had lower E than their B counterparts; the size and material properties of L/R leaves were intermediate between those of T and B leaves. In general, A, P, and E decreased from the base to the tip of shoots. In addition to anisophylly, the influence of gravity induced petiole bending and torsion and resulted in the horizontal planation of laminae. This was observed for field‐grown mature plants and etiolated seedlings. Petiole bending and torsion were interpreted as gravimorphogenetic phenomena. Anatomically, L, E, and petiole deflection angle Fv measured from the vertical were highly correlated with the combined cross‐sectional areas of phloem fibers and xylem in petioles of B leaves and when data from all leaves were pooled. It is tentatively advanced that the correlation of E with the transverse areas of phloem fibers and xylem is evidence that either the pattern or the extent of lignification of petiole tissues is influenced by petiole position with respect to gravity.
PERIDIAL DEVELOPMENT IN GLOMUS MOSSEAE (GLOMACEAE)
Authors: Meier R. , Charvat I.
Published: January 2018

Unispored sporocarps of a Kansas isolate of G. mosseae at all stages of development were prepared for light and scanning electron microscopy to reveal the process involved in peridium formation and spore release. Five stages were identified: 1) peridial hyphal branch origination from below the sporophore attachment; 2) continued peridial hyphal branching and weft formation; 3) adherence of peridial hyphae to the spore wall and completion of peridial expansion into mature state; 4) separation of the primary (evanescent) spore wall layer from the spore and the inner peridial layer; and 5) release of the de‐peridiate spore. Spores in stage 3 were surrounded by a two‐layered peridium consisting of thinner‐walled, parallel‐arranged hyphae next to the spore and thicker‐walled, jigsaw puzzle‐arranged hyphae to the outside; the latter of which collapsed during stages 4 and 5. Fine radial canals and lignituberlike ingrowths were seen in both the de‐peridiate spore wall and, for the first time, in the shed peridium. Comparison of these results with studies of related sporocarpic genera lead to the conclusion that the process of peridium formation in G. mosseae is similar to that of G. coronatum, but that other sporocarpic Glomus representatives must be characterized before valid comparisons may be drawn.
VARIATION IN MALE AND FEMALE REPRODUCTIVE SUCCESS AMONG FLORAL MORPHS IN THE TRISTYLOUS PLANT LYTHRUM SALICARIA (LYTHRACEAE)
Authors: O'Neil Pamela
Published: January 2018

The purpose of this study was to assess variation in male and female reproductive success among the three morphs of the tristylous plant, Lythrum salicaria. Fluorescent dyes were used as pollen analogs to determine whether morphs differ in their abilities to donate and receive pollen, and actual and potential seed set was measured with a hand pollination experiment. Dye transfer among morphs was highly asymmetric, with more frequent transfer from the short‐styled morph to the long‐ and mid‐styled morphs. This suggests that shorts are performing better at pollen donation and longs and mids are performing better at pollen receipt. All flowers on 95 plants were hand pollinated to test whether female reproductive success is more pollen‐limited in the short‐styled morph than in other morphs. Hand‐pollinated short‐styled plants had significantly higher total seed mass and more seeds per capsule than short controls, whereas hand pollination failed to increase seed set in long and mid morphs. As predicted, short‐styled morphs showed significant pollen limitation, whereas seed set in long‐ and midstyled morphs was not pollen‐limited. Thus, in Lythrum salicaria asymmetrical pollen flow generates morph‐specific differences in male and female fitness.
BIPARENTAL INBREEDING DEPRESSION IN THE SELF‐INCOMPATIBLE ANNUAL PLANT GAILLARDIA PULCHELLA (ASTERACEAE)
Authors: Heywood John S.
Published: January 2018

Biparental inbreeding is thought to be a common feature of plant populations with restricted pollen dispersal. It is generally assumed that the inbreeding depression frequently observed to accompany self‐fertilization can be extrapolated to the lesser degrees of consanguinity involved in biparental inbreeding, but this is virtually untested. To test this assumption, seeds collected from a single natural population of the self‐incompatible annual Gaillardia pulchella were used to generate full‐sib families derived by crossing either noninbred full‐sibs (inbred families) or noninbred nonrelatives (outbred families). Members of each family were divided between high‐stress and low‐stress treatments that differed in soil volume and nutrient level. Inbred seedlings had a lower chance of survival, were more likely to be morphologically abnormal, and grew more slowly than outbred seedlings, indicating the presence of biparental inbreeding depression. Stress treatment had no significant effect on inbreeding depression, and no family stress‐environment interactions were detected. Inbreeding did not increase the among‐family variance in growth rate, suggesting that inbreeding depression of growth rate is caused by many genes with small individual effects. Relative to direct estimates of inbreeding depression, observed levels of near‐neighbor outcrossing depression, presumed to be biparental inbreeding depression, are surprisingly high in many plant species.
DUPLICATE GENE EXPRESSION FOR ISOCITRATE DEHYDROGENASE AND 6‐PHOSPHOGLUCONATE DEHYDROGENASE IN DIPLOID SPECIES OF ELEUSINE (GRAMINEAE)
Authors: Werth Charles R. , Hilu Khidir , Langner Clara A. , Baird Wm. Vance
Published: January 2018

In the course of a survey of isozyme variation in the grass genus Eleusine, complex band patterns were observed for the enzymes isocitrate dehydrogenase (IDH) and 6‐phosphogluconate dehydrogenase (6PGD). These patterns were interpreted as the result of duplicate expression for one of the two genes that ordinarily codes subcellularly compartmentalized forms of each of these enzymes. The interpretation of IDH phenotypes was facilitated by intraspecific allelic variation at one of the putatively duplicated genes (Idh‐2), and was verified by examining phenotype ratios in progeny arrays from selfed heterozygotes of E. indica. The lack of analogous intraspecific variation for 6PGD precluded genetic tests, but the duplicate nature of expression was supported by interspecific patterns of variation. Four out of the five diploid species of Eleusine studied (E. indica, E. jaegeri, E. multiflora, E. tristachya) exhibited both duplications; E. floccifolia appeared to lack the IDH duplication, but possessed the 6PGD duplication. Both enzymes showed evidence of hyperduplication in the tetraploid species E. coracana.
FLORAL BIOLOGY OF NEPENTHES GRACILIS (NEPENTHACEAE) IN SUMATRA
Authors: Kato Makoto
Published: January 2018

Nepenthes gracilis, a dioecious carnivorous plant, has inconspicuous flowers lacking petals. Nectaries distributed on the upper surface of four sepals secrete dilute nectar (3%–12% sugar concentration) at night, but the nectar immediately disappears during the day by evaporation in the sunny environment of Sumatra. Male flowers have a higher nectar production rate but lower sugar concentration of nectar than female flowers. Flowers of both sexes were visited by pyralid moths at night and by calliphorid flies in the evening. Pollen was found attached on these insects visiting Nepenthes flowers. The pattern of nectar production of sepals is regarded as attracting nocturnal flying insects and avoiding ants, while the pitchers attract ants by nectar secreted on the pitcher rim.
Evidence from chloroplast DNA restriction site analysis on the relationships of Scalesia (Asteraceae: Heliantheae)
Authors: Schilling Edward E. , Panero José L. , Eliasson Uno H.
Published: January 2018

Chloroplast DNA restriction site variation provided data with which to compare the Galápagos Island endemic Scalesia to potential sister groups within subtribe Helianthinae. Pappobolus is suggested by these data to be the most likely sister group to Scalesia. It is an Andean endemic genus that includes the South American species once regarded as a subgenus of Helianthus and later assigned to Helianthopsis. Two other groups considered as potential sister groups based on their geographic distribution in South America were not placed near Scalesia in the most parsimonious tree. Viguiera sect. Diplostichis appears to be relatively basal within subtribe Helianthinae, and the South American species of Viguiera, although previously classified in more than one subgenus, appear to form a single, monophyletic group that is not the sister group to Scalesia. The minimum of ten restriction site differences between Scalesia and Pappobolus of approximately 525 sites surveyed yielded an estimated sequence divergence of 0.19%, and an estimated time of divergence of approximately 1.9–6.2 million years.
Tree and shrub dynamics in northwestern Great Basin woodland and shrub steppe during the Late‐Pleistocene and Holocene
Authors: Nowak Cheryl L. , Nowak Robert S. , Tausch Robin J. , Wigand Peter E.
Published: January 2018

During the last 12,000 to 30,000 years, a large proportion of the dominant trees and shrubs in modem assemblages of woodland and shrub steppe vegetation in the northwestern Great Basin have undergone relatively small changes in their geographic ranges. A woodland tree, Juniperus osteosperma, has an extensive temporal and spatial fossil record from 11 woodrat midden locales that were sampled in the northwestern Great Basin. Above 1,300 m elevation, J. osteosperma has been continuously present in that fossil record for at least the last 30,000 years. However, J. osteosperma was lost at elevations below 1,300 m sometime during the last 10,000 years, during the Holocene. Although the elevational ranges of six shrub taxa show changes during the Holocene, geographic ranges of 11 other shrub taxa have been largely static. Of the woodland and shrub steppe species examined, Pinus monophylla has experienced the greatest change in its geographic range during the late‐Pleistocene and Holocene. Pinus monophylla has migrated northward across the Great Basin from Pleistocene refugia in the southern portions of this region. The rate of latitudinal migration was more rapid along the eastern side of the Great Basin than on the western side. Thus, the species that comprise modern woodland and shrub steppe communities of the northwestern Great Basin appear to have two strategies to cope with climate change. First are species, as exemplified by J. osteosperma, whose geographic ranges were relatively insensitive to climate change and are termed orthoselective species. High genetic variation within species and the formation of coenospecies likely allowed these species to cope with climatic change by genetic adaptation. Secondly, other species, as exemplified by P. monophylla, have experienced shifts in their geographic range during past climate changes and more clearly fit the migration model of species response to climate change.
Does nonrandom mating among wild radish plants occur in the field as well as in the greenhouse?
Authors: Marshall Diane L. , Fuller Ollar S.
Published: January 2018

We tested whether nonrandom mating can occur across a range of conditions in wild radish by performing experimental crosses on plants grown under three greenhouse and one field regime. Variation in maternal condition among treatments was sufficient to alter components of reproduction. Effects of pollen donor identity on total seed mass per fruit were significant overall and stronger in the greenhouse than the field treatment. Mating was nonrandom in the field and in some, but not all greenhouse treatments. Selective filling of multiply sired fruits tended to occur in all treatments but was most pronounced in the low‐water and defoliation treatments as performed in the greenhouse. Our results demonstrate that nonrandom mating is possible in the field, so patterns of nonrandom mating found in previous studies of wild radish are not likely to be artifacts of greenhouse conditions. However, we also discovered that there may be limits to the range of maternal conditions under which these processes occur.
Bottleneck‐induced dissolution of self‐incompatibility and breeding system consequences in Aster furcatus (Asteraceae)
Authors: Reinartz James A. , Les Donald H.
Published: January 2018

Aster furcatus is a rare species with extremely limited genetic variation at isozyme loci. We utilized crossing experiments and seed set data obtained from natural populations to verify that there is also little allelic variation at the self‐incompatibility (S) locus. Seed set in several populations was limited by a low number of S‐alleles. Associated with a low number of S‐alleles in populations was the dissolution of the incompatibility system, manifest by individual variation in self‐compatibility, and by complex dominance relationships among S‐alleles. Plant self‐compatibility was correlated with mean number of ovules per inflorescence. Thus, self‐compatibility appeared to be under partial environmental influence. Computer simulations revealed that the shapes of seed set distribution curves of modeled self‐incompatible plant populations depend on the number of incompatibility alleles in the populations. By varying the number of S‐alleles in modeled populations, we generated seed set distribution curves similar to those of natural populations. Genetic bottlenecks reduce the number of S‐alleles and the proportion of compatible matings in populations of multiallelic self‐incompatible species. Self‐compatible genotypes are at a selective advantage in populations that lack a sufficient number of S‐alleles to produce compatible crosses. Aster furcatus appears to be evolving self‐compatibility as a result of bottleneck‐induced losses of S‐alleles.
Pollen tube pathway through the gynoecium of Monotropsis odorata (Monotropaceae)
Authors: Olson A. Randall
Published: January 2018

Monotropsis odorata Elliott. is one of the most cryptic and relatively rare North American endemic species of the Monotropaceae; therefore, information concerning the biology of this achlorophyllous, mycotrophic angiosperm is limited. Bright field and fluorescence microscopic investigations of postpollination gynoecia reveal that pollen tubes follow a continuous pathway from the receptive surface of the stigma to micropyles of the ovules. The pollen tube pathway is characterized by discrete strands of transmitting tissue connecting an exudate‐coated stigma to an exudate‐filled, stylar canal that leads directly to exudate‐coated placentae. Pollen tube growth appears restricted to those areas associated with an exudate. The gynoecial pathway for pollen tube growth in this taxon conforms to those described from other monotropàceous species.
Size‐number trade‐offs and pollen production by Papilionaceous legumes
Authors: Vonhof Maarten J. , Harder Lawrence D.
Published: January 2018

The intra‐ and interspecific relations between the size and number of pollen grains were examined for 21 species of papilionaceous legumes to test for the trade‐off expected from the subdivision of limited resources. We observed a tradeoff between pollen grain diameter and the number of grains produced per flower within 17 of the 21 species examined. For 12 of these species, the observed partial regression coefficient for In (pollen grain diameter) equaled ‐3, as expected. The remaining five species exhibited more negative partial regression coefficients than expected. Relations between pollen grain size and number that are more negative than expected may result from a decelerating relation between pollen grain size and the resource investment per grain. Flower production significantly influenced pollen production for only eight species so that pollen production seems to be determined primarily on a per flower basis. Interspecifically, pollen size also varied inversely with pollen number for the 21 species even after the effect of phylogenetic relatedness was removed. Pollen size varies relatively little compared to the number of pollen grains produced per flower and therefore may be the primary target of natural selection. The presence of a trade‐off in pollen production probably constrains the evolutionary options by which flowering plants can maximize male success.
WATER RELATIONS OF WATER‐STRESSED, SPLIT‐ROOT C4 (SORGHUM BICOLOR; POACEAE) AND C3 (HELIANTHUS ANNUUS; ASTERACEAE) PLANTS
Authors: Zhang Jingxian , Kirkham M. B.
Published: January 2018

Sorghum [Sorghum bicolor (L.) Moench] and sunflower (Helianthus annuus L.) were grown in a greenhouse with roots divided between sand irrigated with nutrient solution (–0.097 MPa) or nutrient solution containing polyethylene glycol (PEG) (–0.570 MPa) to compare the effect of unequal root zone stress on plant water relations of a C4 (sorghum) and a C3 (sunflower) plant. Roots also were divided between two pots of sand irrigated only with nutrient solution (controls) or only with PEG in nutrient solution. In addition to plant water‐status measurements, photosynthetic rate, growth (height, root, and shoot dry weights), and evolution of ethylene (a gaseous hormone indicative of stress) were measured. Under all three split‐root treatments, sunflower had a lower leaf water potential and produced more ethylene than sorghum. Sunflower was able to survive the PEG stress if half of its root system was under nonstressed conditions. Sunflower with half its root system irrigated with PEG usually had values of leaf water potential, osmotic potential, stomatal resistance, transpiration rate, photosynthetic rate, ethylene evolution, height, and dry weights that were close to those of the control plants. Sunflower with all roots exposed to PEG was wilted severely. Sorghum was little affected by PEG stress applied either to half or all the root system. Growth of sorghum was the same under all treatments. Apparently because stomata of sorghum were more closed in the partial stress test than those of sunflower, sorghum conserved water and had a higher leaf water potential, which might have permitted growth with stress.