bluuebunny/crossref_metadata_2025 huggingface dataset:
INFLUENCE OF NEIGHBORS ON TREE FORM: EFFECTS OF LATERAL SHADE AND PREVENTION OF SWAY ON THE ALLOMETRY OF LIQUIDAMBAR STYRACIFLUA (SWEET GUM)
Authors: Holbrook N. Michele , Putz Francis E.
Published: January 2018

Liquidambar styraciflua (sweet gum) saplings were open grown (control), guy‐wired to prevent wind‐induced sway (constrained), or guy‐wired within open‐topped shade cloth cylinders to simulate shading by neighboring trees (shaded). Mechanical stability was assessed after 2 years of growth by field measurement of whole‐tree flexibility and with the critical buckling height predictions of five allometrical models. Data from this experiment are supplemented with measurements of sweet gum trees growing in a 9‐year‐old pine plantation; individuals crowded but not overtopped by pines are compared with similar‐aged trees growing in openings within the plantation.

Changes in aboveground architecture were stimulated by both prevention of sway and lateral shade but the effect of the latter was most pronounced; shaded saplings approached or exceeded their calculated critical height and buckled under their own weight when the shade cloth cylinders were removed. Rates of aboveground biomass acquisition, total leaf area, wood density, and wood elastic moduli did not differ among the three treatments; changes in stem allometry accounted for most of the observed differences in tree stability. Sweet gum trees growing in a pine plantation responded similarly to neighbors; crowded trees had larger height: diameter ratios and more closely approached their calculated critical heights than did trees growing in the open. Sweet gum saplings growing in dense stands of similar‐sized plants may surmount their neighbors by allocating relatively more wood to height growth than to girth increment.
EMBRYO SAC DEVELOPMENT IN THE CV. KS MALE‐STERILE, FEMALE‐STERILE LINE OF SOYBEAN (GLYCINE MAX)
Authors: Benavente R. Sandra , Skorupska Halina , Palmer Reid G. , Shoemaker Randy C.
Published: January 2018

Light microscopic observations were made on 22 ovules from fertile plants and 108 ovules from sterile plants of the cv. KS synaptic mutant, a highly male‐sterile, female‐sterile line of soybean [Glycine max (L.) Merr.] (2n = 2x = 40). Ovules of fertile siblings contained normal embryo sacs and embryos. Ovules from sterile plants contained various irregularities. The most consistent abnormality was the failure of the embryo sac to attain normal size. Small megasporocytes of irregular shape were seen; only one megasporocyte of normal shape and size was noted. No linear tetrads were found. However, two ovules contained nonlinear triads. A range from zero to 28 cells and nuclei, of various sizes, were identifiable in small megagametophytes and embryo sacs. Degeneration of these nuclei and cells was noted as early as the four‐nucleate gametophyte stage. Other ovules contained degenerated nucellar centers without embryo sacs. Two ovules appeared to be normal. Late postpollination stages were marked by shrunken nucellus and integuments. The presence of pollen tube traces, endosperm, and aborting embryos in ovules of hand‐pollinated flowers from sterile plants suggested that no incompatibility was involved. Degeneration of the gametophyte and embryo sac contents at many developmental stages indicated a wide array of effects, possibly resulting from meiotic irregularities similar to those seen in microsporogenesis of this mutant.
REGENERATION BY FRAGMENTATION IN TROPICAL MONTANE FOREST SHRUBS
Authors: Kinsman Sharon
Published: January 2018

The ability of neotropical forest shrubs to reproduce by establishment of severed fragments was demonstrated experimentally in a lower montane forest in Costa Rica. Twigs (N = 307) broken from 78 individual shrubs or large herbs (representing 22 species, 14 genera, and eight families) were individually marked, dropped to the forest floor, and measured periodically over 5 years. Ninety‐two percent of the fragments and all but one species persisted for 4 months (rainy season) or more. Adventitious roots were produced after the first month. For all fragments, both the net number of leaves and total stem length declined initially. Mortality was concentrated in a 10‐month period (that included the first dry season), in which 35% of the fragments (average by species) and 85% of the species survived. Species’ survivorship then was steady or declined slowly. Fourteen species, representing seven genera in three families (Piperaceae, Rubiaceae, and Acanthaceae) persisted for all 5 years of the study. A fragment's original size did not affect the likelihood that it would survive. Although there was continuous production of new leaves, few fragments showed a net gain in leaf number by 5 years. In contrast, most fragments showed a net gain in stem length (up to five‐fold), with vertical growth accounting for the gain. By the third year, most surviving fragments were upright plants and some had flowered and borne fruit. Several, broken again by falling branches, fragmented naturally. Regrowth from fragments is likely to be important in the persistence of individuals and in the structure and dynamics of populations of shrubs in tropical wet forests.
COMPARATIVE ANATOMY OF THE SPIKELET CALLUS OF ERIOCHLOA, BRACHIARIA, AND UROCHLOA (POACEAE: PANICEAE: SETARIINEAE)
Authors: Thompson Rahmona A. , Tyrl Ronald J. , Estes James R.
Published: January 2018

Anatomical investigation of the spikelet base in Eriochloa reveals a nonvascularized cup‐shaped structure composed of large parenchyma cells surrounding a column of tissue that is continuous with the pedicel. The cup and column are fused only at the base of the cup. No vestigial stelar node occurs in either the cup or the column. The stele branches above the cup at the rachillar node of the second glume. Therefore, the cup‐shaped callus characteristic of Eriochloa appears to be formed entirely of parenchymatous tissue and is not derived from the first glume as previously interpreted. The bead of callus at the base of the spikelet in some species of Brachiaria also comprises an unbranched stele surrounded by parenchyma. The vascular tissue branches and enters the first glume at the apex of the bead. The spikelet base of Urochloa has a distinct first glume, nodal complex, and no callus parenchyma. Thus, the cup‐shaped callus of Eriochloa and the callus bead of Brachiaria appear to be structurally similar.
FOSSIL CERATOPHYLLUM (CERATOPHYLLACEAE) FROM THE TERTIARY OF NORTH AMERICA
Authors: Herendeen Patrick S. , Les Donald H. , Dilcher David L.
Published: January 2018

Fossil fruits and a vegetative axis assignable to the extant genus Ceratophyllum are described from four North American Tertiary localities. Fossil fruits assignable to the extant species C. muricatum and C. echinatum are reported from the Eocene Green River and Claiborne formations, and the Miocene Esmerelda Formation, respectively. An extinct species, C. furcatispinum, is described from the Paleocene Fort Union Formation and represents the oldest published report of Ceratophyllum in the fossil record. The existence of extant angiosperm species in the Eocene is very unusual and may be attributable in this case to slow evolutionary rates and unusual evolutionary properties associated with hydrophily in the genus Ceratophyllum.
POLLEN MORPHOLOGY AND SYSTEMATICS OF SIPHONOGLOSSA SENSU LATO (ACANTHACEAE)
Authors: Hilsenbeck Richard A.
Published: January 2018

Pollen morphology of 15 species ofSiphonoglossaand of two closely related groups was investigated. Two tribal‐specific pollen types are found withinSiphonoglossasensu lato suggesting that the genus is artificial, composed of taxa belonging in several genera among two tribes (subtribes sensu Bremekamp) of Acanthaceae. Five taxa currently included in an informal subgeneric category ofSiphonoglossahave tricolporate, prolate pollen (termed Type I) that is characteristic of Odontonemeae (= Odontoneminae, Justicieae). Pollen of the remaining taxa, belonging in two formal sections of the genus, are mostly 2‐porate, bilateral (Type II) with a sexine sculpturing characteristic of Justicieae (= Justiciinae). Pollen of sectionSiphonoglossais rather uniform, 2‐porate, bilateral with lolongate pores, and seem to delimit a natural group. Taxa of sectionPentalobahave a more heterogeneous pollen morphology, mostly 2‐porate, bilateral with lalongate pores. Controversial aspects of the interpretation of pollen morphology in Justiciinae are presented and their relevance to this study are examined. Hypothetical trends in the evolution of pollen of Justiciinae are discussed and the application of pollen morphology to taxonomy of the genus is presented, including a recommendation for narrowing the generic concept ofSiphonoglossato the taxa of the type section.
COMPARATIVE ONTOGENY OF THE INFLORESCENCE AND FLOWER OF HAMAMELIS VIRGINIANA AND LOROPETALUM CHINENSE (HAMAMELIDACEAE)
Authors: Mione Thomas , Bogle A. Linn
Published: January 2018

A comparative developmental study of the inflorescence and flower of Hamamelis L. (4‐merous) and Loropetalum (R. Br.) Oliv. (4–5 merous) was conducted to determine how development differs in these genera and between these genera and others of the family. Emphasis was placed on determining the types of floral appendages from which the similarly positioned nectaries of Hamamelis and sterile phyllomes of Loropetalum have evolved. In Hamamelis virginiana L. and H. mollis Oliv. initiation of whorls of floral appendages occurred centripetally. Nectary primordia arose adaxial to the petals soon after the initiation of stamen primordia and before initiation of carpel primordia. In Loropetalum chinense (R. Br.) Oliv. floral appendages did not arise centripetally. Petals and stamens first arose on the adaxial portion, and then on the abaxial portion of the floral apex. The sterile floral appendages (sterile phyllomes of uncertain homology) were initiated adaxial to the petals after all other whorls of floral appendages had become well developed. In all three species, two crescent shaped carpel primordia arose opposite each other and became closely appressed at their margins. Postgenital fusion followed and a falsely bilocular, bicarpellate ovary was formed. Ovule position and development are described. The nectaries of Hamamelis and sterile phyllomes of Loropetalum rarely develop as staminodia, suggesting a staminodial origin. However, these whorls arise at markedly different times and are therefore probably not derived from the same whorl of organs in a common progenitor. This hypothesis seems probable when one considers that the seemingly least specialized genus of the tribe, Maingaya, bears whorls of both staminodia and sterile phyllomes inside its whorl of stamens.
CONTRASTING STOMATAL RESPONSES TO VARIABLE SUNLIGHT IN TWO SUBALPINE HERBS
Authors: Knapp Alan K. , Smith William K.
Published: January 2018

Gas exchange was measured in two subalpine herbs during alternating periods of sun and shade that simulated natural cloud patterns. Stomatal conductance (g) in the subalpine herb Helianthella quinquenervis was reduced by as much as 75% during 5‐min shade periods that ranged in photosynthetic photon flux density (PPFD) from 100 to 1,100 μmol m–2 sec–1. In contrast, responses in g in another herb, Frasera speciosa, to fluctuations in sunlight were small, apparently due to slower stomatal responses. Based on an earlier hypothesis that water stress may strongly influence nonsteady state gas exchange responses to fluctuations in PPFD, net photosynthesis and g were measured in these herbs as seasonal water stress increased and compared with responses in irrigated plants. Stomatal conductance was relatively unresponsive to changes in PPFD in F. speciosa regardless of water stress. In contrast, substantial decreases in g occurred for H. quinquenervis during shade only when this species experienced water stress later in the season. Little response in g was measured early in the season or in irrigated plants. The seasonal shift in nonsteady state responses in H. quinquenervis from little response in g to shade when plants were nonstressed to more rapid reductions in g as water stress increased would maximize carbon gain early in the season when soil water was abundant while conserving water during periods of soil drought.
SEASONAL CHANGES IN THE APICAL ZONATION AND ULTRASTRUCTURE OF COASTAL DOUGLAS FIR SEEDLINGS (PSEUDOTSUGA MENZIESII)
Authors: Krasowski M. J. , Owens J. N.
Published: January 2018

The apical meristems of one‐year‐old container‐grown seedlings of coastal Douglas fir were studied in two years during embryonic shoot development, dormancy, and dormancy release by light and electron microscopy. Apical zonation was evident at all times but prominence of some zones varied. Vacuolation was an important zone‐characteristic and was not an artifact created by lipid extraction. During late summer and fall the plasma membrane was relatively smooth, ER not abundant, nuclear membranes irregular, and lipid bodies sparse. Numerous autophagic vacuoles occurred in apical cells. These diminished after bud scale initiation was completed in September and reappeared again in midwinter. Maximum starch accumulation was in the fall then it decreased during the winter and remained low during cold storage. The number of lipid bodies gradually increased in late fall and was large in winter. A single night of –1 C caused an increase in the number of lipid bodies. Plastids contained electron‐dense material which accumulated further under subfreezing temperatures and eventually appeared to be released during winter into the cytoplasm and arranged into small globules along the cisternae of the ER. Granular protein bodies were observed at this time as well as deposits of electron‐dense material on the outer surface of the plasma membrane and in cell walls. During winter, the plasma membrane became convoluted, short cisternae of the ER abundant, the nuclear membranes evenly separated, and nucleolar components aggregated. At the end of dormancy, ribosomes and starch grains became very abundant. Most lipid bodies diminished by budbreak.
EVOLUTION OF THE CASUARINACEAE: MORPHOLOGICAL COMPARISONS OF SOME EXTANT SPECIES
Authors: Dilcher David L. , Christophel David C. , Bhagwandin Harry Omroa , Scriven Leonie J.
Published: January 2018

The Casuarinaceae consists of the 4 genera Gymnostoma, Ceuthostoma, Casuarina and Allocasuarina. All the genera are found living today in Australia, Malaysia, Melanesia, and Southeast Asia. An abundant and widespread fossil record of the genus Gymnostoma is known from New Zealand, Argentina, South Africa, and Australia. This paper provides a compilation of basic vegetative and reproductive morphological data of the 4 genera of the Casuarinaceae with special emphasis on these features in Gymnostoma. The features are presented in tabular form and the data are compared and discussed. Most of the genera can be clearly distinguished by the morphology of their vegetative and reproductive organs. Species differences within the extant genera often are difficult to distinguish; therefore, comparative systematic analysis of these fossils from fragmentary and incomplete remains ranging through time will be very difficult, and care must be taken when interpreting evolutionary trends from them.
EVOLUTIONARY STUDIES OF ATRIPLEX: PHYLOGENETIC RELATIONSHIPS OF ATRIPLEX PLEIANTHA
Authors: Stutz Howard C. , Chu Ge‐Lin , Sanderson Stewart C.
Published: January 2018

Atriplex pleiantha Weber differs from all other species of Atriplex in having 1) multiple female flowers subtended by two bracts, 2) female flowers with a perianth, and 3) embryos with radicles pointing downwards. Because of these significant differences it is proposed that Atriplex pleiantha be elevated to the level of a separate genus and be designated Proatriplex pleiantha (Weber) Stutz & Chu. The closest relatives of Proatriplex appear to be Archiatriplex, Endolepis, Exomis, and Microgynoecium. These are all diploid, monoecious annuals, have non‐Kranz type leaf anatomy, and female flowers with a perianth.
KARYOTYPIC STUDIES IN SOLANUM SECTION BASARTHRUM (SOLANACEAE)
Authors: Bernardello Luis M. , Anderson Gregory J.
Published: January 2018

Mitotic chromosomes of 450 individuals, representing 59 accessions of 18 of the 22 species of Solanum sect. Basarthrum were studied. Statistical analyses of chromosome length, genome length, and centromere position yielded estimates of karyotype composition and asymmetry. A generalized karyotype of the section shows that most of the chromosomes are metacentric (44%) or submetacentric (53%). A general trend emerged: the greater the total genome length, the more asymmetric the karyotype. However, karyotype asymmetry does not seem to be based on major chromosomal rearrangements. There is variation in species groups in the karyotype formula, and chromosome length differences were useful in distinguishing series. Patterns of cytological variation reinforce the systematic arrangement of the taxa based on morphological, chemical, and molecular studies. Chromosomal differences characterize most of the species. Five species bear subtelocentric chromosomes, two have telocentrics, and two have satellites. The genomes of the staminate and pistillate plants of the dioecious S. appendiculatum are identical. Of the species proposed as progenitors of the domesticated cultigen S. muricatum, S. caripense is the most similar karyotypically.
INFLUENCE OF ELECTRICAL FIELDS AND ASYMMETRIC APPLICATION OF MUCILAGE ON CURVATURE OF PRIMARY ROOTS OF ZEA MAYS
Authors: Marcum Heidi , Moore Randy
Published: January 2018

Primary roots of Zea mays cv. Yellow Dent growing in an electric field curve towards the anode. Roots treated with EDTA and growing in electric field do not curve. When root cap mucilage is applied asymmetrically to tips of vertically‐oriented roots, the roots curve toward the mucilage. Roots treated with EDTA curve toward the side receiving mucilage and toward blocks containing 10 mm CaCl2, but not toward “empty” agar blocks or the cut surfaces of severed root tips. These results suggest that 1) free calcium (Ca) is necessary for root electrotropism, 2) mucilage contains effector(s) that induce gravitropiclike curvature, and 3) mucilage can replace gravitropic effectors chelated by EDTA. These results are consistent with the hypothesis that the downward movement of gravitropic effectors to the lower sides of tips of horizontally‐oriented roots occurs at least partially in the apoplast.
BIOCHEMICAL HETEROPHYLLY AND FLAVONOID EVOLUTION IN NORTH AMERICAN POTAMOGETON (POTAMOGETONACEAE)
Authors: Les Donald H. , Sheridan Donna J.
Published: January 2018

Morphologically heterophyllous species of Potamogeton also commonly display biochemical heterophylly with respect to flavonoid compounds. Generally, floating leaves contain an assortment of flavonoids, whereas submersed leaves often exhibit reduced flavonoid profiles. In strictly submersed (homophyllous) species, two patterns occur. Linear‐leaved species have few flavonoids and their biochemical profiles resemble those of submersed leaves of heterophyllous species. Broad‐leaved homophyllous species possess flavonoid profiles more similar to those of the floating leaves of heterophyllous species. Numerical analysis of these chemical data is consistent with phylogenetic relationships within the genus derived independently on the basis of morphological and chromosomal data. Glycoflavones, which are probably maintained in floating leaves because of their UV filtering ability, exhibit the most pronounced biochemical heterophylly in Potamogeton. The lack of glycoflavones in submersed leaves of heterophyllous species and in linear‐leaved homophyllous species is attributable to the ability of naturally colored water to significantly absorb harmful UV radiation. These observations provide strong support for earlier hypotheses suggesting the importance of flavonoid evolution in the conquest of exposed terrestrial habitats by plants.
VA MYCORRHIZAE IN STRAND VEGETATION OF HAWAII: EVIDENCE FOR LONG‐DISTANCE CODISPERSAL OF PLANTS AND FUNGI
Authors: Koske R. E. , Gemma J. N.
Published: January 2018

Vesicular‐arbuscular mycorrhizal fungi (VAMF) were a nearly constant component of the coastal strand of the Hawaiian Islands, occurring in beach sand, driftline debris, in roots of 23 of 31 species of vascular plants examined, and in association with rhizomes of two native species, Sporobolus virginicus and Jacquemontia sandwicensis. Mycorrhizae were most frequent and intensity of VAM development was greatest in endemic plants, less in indigenous species, and least in alien species. Spores of VAMF were produced in abundance between the rhizome and the leaf sheaths of Sporobolus. Roots of two strand species, including roots of Sporobolus that were immersed in seawater for 7 days, functioned as inocula of VAMF in pot‐culture studies. The close association between propagules of VAMF and vegetative fragments of indigenous plants found in the present study suggests a mechanism of codispersal that appears to ensure the maintenance of the symbiosis in nutrient‐deficient sites where it is most beneficial. The codispersal of fungus and plant may explain the high frequency of mycotrophy in strand species in the tropical Pacific.
DEVELOPMENTAL CYCLES IN SHOOT GROWTH OF MALE CYCAS CIRCINALIS
Authors: Bork Joyce
Published: January 2018

Cycles of development in several male shoots of Cycas circinalis were studied by counting sequences of foliage leaves, scale leaves, and cones by observation of either their scar patterns or vascular remains. Although male cones are always produced subsequent to a cycle of foliage leaves and are fairly regularly spaced there is no obvious correlation between their presence and the previous cycles of leaves. Ratios of foliage leaves to scale leaves in each cycle are variable. The primary diameter of the axis is obconical, but a conical stem form results from secondary growth. The result of concentric development of xylem and phloem is positively correlated with stem diameter rather than stem age.
RELATIONS BETWEEN SUNFLECK SEQUENCES AND PHOTOINHIBITION OF PHOTOSYNTHESIS IN A TROPICAL RAIN FOREST UNDERSTORY HERB
Authors: Gouallec J. L. Le , Cornic G. , Blanc P.
Published: January 2018

We report the photosynthetic characteristics of a C3 shade plant native to the tropical rain forest understory. It was shown that Elatostema repens Lour. (Hall) f. (Urticaceae) presents a large light adjustment capacity. The effects of several lightfleck sequences on photoinhibition of photosynthesis and carbon gain are analyzed. Photoinhibition is measured both as a decrease in leaf net CO2 uptake in limiting light (shown to be linearly correlated to quantum yield of O2 evolution measured at saturating CO2) and as a decrease of the ratio of variable fluorescence (Fv) to maximum fluorescence (Fmax) measured in liquid nitrogen. It is shown that lightflecks (from 10 to 30 min in duration) of 700 μmol m–2 s–1 (high light) induce photoinhibition, and that the effects of those successive high light periods are additive; there is apparently no recovery from photoinhibition during the low light periods (from 10 to 45 min in duration). In contrast, the Fv/Fmax ratio, though decreasing similarly to quantum yield of net CO2 uptake on leaves submitted to a continuous illumination of 700 μmol m–2 s–1, is only decreased a little on leaves submitted to lightfleck sequences of the same photon flux density. Lightflecks of 250 μmol m–2 s–1 are not photoinhibitory. Compared to the control maintained under light growth condition (40 μmol m–2 s–1) carbon gain is increased on leaves submitted to lightflecks; this gain remains high throughout the light cycles on leaves submitted to nonphotoinhibitory lightflecks and to the photoinhibitory lightflecks followed by the shortest low light period. In the other cases, carbon gain, higher than that of the control at the beginning of the treatments, decreases and becomes lower than the control carbon gain. Finally, the relevance of photoinhibition in the tropical rain forest understory environment is discussed.
EVIDENCE OF PARTIAL APOMIXIS IN ANTENNARIA MEDIA (ASTERACEAE: INULEAE) DETECTED BY THE SEGREGATION OF GENETIC MARKERS
Authors: Bayer Randall J. , Ritland Kermit , Purdy Brett G.
Published: January 2018

The interplant variation in sexual and asexual reproduction in an Oregon population of the alpine perennial Antennaria media was investigated. Four polymorphic loci were assayed by enzyme electrophoresis of the progeny of 72 families from two subpopulations of A. media. The population was divided into two spatially distinct subpopulations. A multilocus model, incorporating a mixture of apomixis and random outcrossing, was used to estimate the mating system of pistillate plants both on the population and individual levels with statistical significance of the estimates based on bootstrap methods. The population contained a mixture of sexual individuals, partial apomicts, and obligate apomicts. The first subpopulation contained individuals that were partially apomictic and presumably produced both reduced and unreduced embryo sacs. There was a conspicuous difference in the breeding system composition between the two subpopulations. The first subpopulation had a “female” biased gender ratio and contained mostly obligate apomicts, some partial apomicts, and some outcrossing amphimicts. The second subpopulation, which had a nearly balanced gender ratio, contained mostly amphimicts, some obligate apomicts, but no facultative apomicts. This is the first study to document partial apomixis in individual plants by the use of genetic markers.
AGE STRUCTURE OF PHORADENDRON JUNIPERINUM (VISCACEAE), A XYLEM‐TAPPING MISTLETOE: INFERENCES FROM A NON‐DESTRUCTIVE MORPHOLOGICAL INDEX OF AGE
Authors: Dawson Todd E. , King Edward J. , Ehleringer James R.
Published: January 2018

We investigated the age‐structure of the xylem‐tapping mistletoePhoradendron juniperinumin relation to characteristics of its host tree,Juniperus osteosperma.We first correlated branch structure in the mistletoe with age of the mistletoe infection as determined anatomically; this correlation provided a nondestructive, field method of obtaining age structure information. We then surveyed the mistletoe plants, applying our aging index, within a population of their host trees in southwestern Utah; the majority of mistletoe plants were 2–12 years old. This peak in abundance of mistletoe infections showed no correlation to total annual precipitation within or 1 year previous to the peaks, minimum winter temperature, or to warmer than average winter temperatures. However, there was a positive correlation (r= 0.51,P< 0.06) with the amount of summer precipitation. A log‐linear analysis indicated that a greater than expected number of mistletoe infections occurred at 5–7 years of age and at approximately 3 m in height among all host trees. We suggest that this pattern resulted because this canopy position had greater leaf and branch areas and was visited most frequently by seed‐dispersing birds. The log‐linear analysis also revealed that fewer than expected mistletoe infections occurred at ages older than 10 years, yet our data indicate that plants can reach 20 years of age. The lack of infections > 10 years of age was correlated to a period of below average precipitation, especially during the growing season, but not with cold winter temperatures, which in other studies had been suggested as a factor influencing mortality. We feel that drought may play an important role in influencing mistletoe mortality through its direct affect on host tree water status, but in addition we offer two alternative hypotheses to explain mistletoe longevity; the first is concerned with the relationship between carbon and nitrogen costs and maintaining large leaf areas in older plants, and the second addresses how increased hydraulic resistance in older and larger plants may be too costly for the plant, and stems are abscised.
BIOMECHANICS OF PSILOTUM NUDUM AND SOME EARLY PALEOZOIC VASCULAR SPOROPHYTES
Authors: Niklas Karl J.
Published: January 2018

The elastic modulus E, flexural rigidity EI, static loading P, and volume fractions V of tissues of the aerial portions of Psilotum nudum are examined in terms of two Voigt models: 1) total elastic modulus ET of a branch element is considered the additive property of the elastic modulus of tissues times their respective volume fraction, i.e., ET = (EV), + (EV)2 + … (EV)n, and 2) ET is considered the product of the elastic modulus of cell walls and the apoplastic volume fraction, i.e., ET = EcwVa. The parameters EI and P, together with the length (l) of each branch element are combined into a dimensionless ratio, Pl2/EI (the load parameter L), to describe the relationship between static loading (Pl2) and the ability to sustain loading (EI). The load parameter of branch elements was found to decrease as the level of branching within aerial portions of this race of Psilotum was ascended. The magnitude of P also decreased acropetally. However, the decrease in L is primarily due to a disproportionate decrease in EI. The load parameter of the basalmost branch of aerial portions is smaller for larger aerial portions of this race of P. nudum. Thus, larger specimens are subtended by more rigid branch elements than smaller aerial portions. The Voigt models provide satisfactory approximations of the data from this race Psilotum and indicate that the principal load supporting tissues are the cortical sclerenchyma and other lignified tissues in older (lower branch elements). The mechanics of the three dimensional branching of P. nudum is extended to consider the aerial portions of some early Paleozoic vascular sporophytes (Algaophyton, Rhynia). Analyses indicate that biomechanical speculation about these fossils is potentially flawed by the ambiguity of anatomical data.
CHARLIEA MANZANITANA, N. GEN., N. SP., AND OTHER ENIGMATIC PARALLEL‐VEINED FOLIAR FORMS FROM THE UPPER PENNSYLVANIAN OF NEW MEXICO AND TEXAS
Authors: Mamay Sergius H.
Published: January 2018

Charliea is a new genus (type‐species: C. manzanitana), based on pinnately compound leaf material from the richly fossiliferous Virgilian (Upper Pennsylvanian) shales of the Kinney Brick Company quarry near Albuquerque, New Mexico. In several features Charliea resembles Russellites or a zamioid cycad. It has linear‐oblong pinnae with broad, oblique attachment and a truncate tip, which is deeply incised to form two to four nearly equal lobes. The venation is simple, parallel, and sparingly dichotomous, each vein ending at the distal margin. The Kinney beds also contain Plagiozamites planchardi, another zamioid form with parallel‐veined pinnae, differing from Charliea chiefly in having rounded tips and veins ending in the denticulate margins. An unnamed third form (genus B) in the Kinney beds has long, narrow pinnae with parallel veins and blunt tips; this strongly resembles the Mesozoic conifer Podozamites, but may just as well represent a cycadophyte. Another unnamed taxon (genus A), from an Upper Pennsylvanian deposit in Jack County, Texas, resembles genus B or Russellites in general shape and venation, but the critical distal margins are unknown. In their single‐ordered parallel venation, these four foliar types contrast sharply with the two‐ordered pinnate venation of most Pennsylvanian fern‐like leaves, and seem to foreshadow Mesozoic morphologies. This tendency toward precocious evolution of parallel‐veined foliar form in North America is also expressed by a single occurrence of the Asiatic, Permian genus Tingia in the Lower Pennsylvanian of Utah, and by the presence of the predominantly Triassic cycadeoid genus Pterophyllum in the Lower Permian of Texas.
PRODUCTION AND EFFECT OF SEED SIZE IN A GRASSLAND ANNUAL (ERODIUM BRACHYCARPUM, GERANIACEAE)
Authors: Stamp Nancy E.
Published: January 2018

Over its fruit maturation period in the field, Erodium brachycarpum (Geraniaceae) exhibited a striking decrease in average seed mass; seeds produced in the 1st week of fruiting were twice the size of those produced 6 weeks later at the time of drought‐induced plant senescence. Individuals with earliest fruit maturation produced the most seeds with the widest range of sizes and over a longer period than the others. In a greenhouse experiment, a similar decline in mean seed weight was generated by inducing drought conditions. Large seeds remained dormant longer and, once the seed coat was scarified, took longer to germinate than small seeds. This study indicates that small E. brachycarpum seeds (36% of the seed pool) produced late in the fruiting period are likely to germinate in the year of seed production, approximately 4–8 months after seed maturation. In contrast, the large seeds (23% of the seed pool), most of which are produced early in the fruiting period, are more likely to germinate in subsequent years (i.e., 15 months or more after seed maturation).
GENETIC VARIATION IN LATHYRUS LATIFOLIUS (LEGUMINOSAE)
Authors: Godt Mary Jo W. , Hamrick J. L.
Published: January 2018

Lathyrus latifolius (everlasting pea) is a perennial vine native to Europe. Naturalized populations of L. latifolius occur in fields and on roadsides over large areas of the United States. Widely cultivated as a garden flower, L. latifolius produces abundant racemes of showy flowers that are bumblebee‐pollinated. The seeds are heavy, large, and round, and exhibit no specialized means of dispersal. Allozyme diversity and population structure were determined for 32 populations of L. latifolius—30 from the southeastern United States and two from Oregon. Results from 21 allozyme loci indicate that genetic diversity is higher and population divergence is lower than expected based on the life history characteristics of the species. No association was found between genetic identity statistics and geographic distance between populations. Although the range in genetic diversity statistics among populations was unusually large, genetic drift did not appear to play a major role in structuring genetic variation. We conclude that the level of genetic diversity maintained within L. latifolius populations, and the level of population divergence found, is strongly influenced by its status as a cultivated garden flower and its human‐associated mode of gene flow via seed dispersal.
HETEROGENEITY IN POLLEN ALLELE FREQUENCIES AMONG CONES, WHORLS, AND TREES OF TABLE MOUNTAIN PINE (PINUS PUNGENS)
Authors: Gibson J. P. , Hamrick J. L.
Published: January 2018

Pinus pungens Lambert (Table Mountain pine) is characterized by serotinous cones that are borne several (two to five) per whorl. Sporophytic and gametophytic tissues from whorls collected in different canopy zones of eight trees were electrophoresed and surveyed for six allozyme loci. Pollen allele frequencies received by individual trees, whorls on trees, and cones in whorls were estimated and used to estimate outcrossing rates and the distribution of genetic diversity within and among each level. Significant differences in pollen allele frequencies were detected at all levels, indicating that the genetic composition of the pollen pool available to different female strobili is heterogeneous. The fine‐scale genetic structure in the seed pool is a record of past reproductive events and is the precursor to genetic structure in the next generation.
POLLINATION DROP IN RELATION TO CONE MORPHOLOGY IN PODOCARPACEAE: A NOVEL REPRODUCTIVE MECHANISM
Authors: Tomlinson P. B. , Braggins J. E. , Rattenbury J. A.
Published: January 2018

Observation of ovulate cones at the time of pollination in the southern coniferous family Podocarpaceae demonstrates a distinctive method of pollen capture, involving an extended pollination drop. Ovules in all genera of the family are orthotropous and single within the axil of each fertile bract. In Microstrobus and Phyllocladus ovules are erect (i.e., the micropyle directed away from the cone axis) and are not associated with an ovule‐supporting structure (epimatium). Pollen in these two genera must land directly on the pollination drop in the way usual for gymnosperms, as observed in Phyllocladus. In all other genera, the ovule is inverted (i.e., the micropyle is directed toward the cone axis) and supported by a specialized ovule‐supporting structure (epimatium). In Saxegothaea there is no pollination drop and gametes are delivered to the ovule by pollen tube growth. Pollination drops were observed in seven of the remaining genera. In these genera the drop extends over the adjacent bract surface or cone axis and can retain pollen that has arrived prior to drop secretion (“pollen scavenging”). The pollen floats upward into the micropylar cavity. The configuration of the cone in other genera in which a pollination drop has not yet been observed directly suggests that pollen scavenging is general within the family and may increase pollination efficiency by extending pollination in space and time. Increased pollination efficiency may relate to the reduction of ovule number in each cone, often to one in many genera, a derived condition. A biological perspective suggests that animal dispersal of large seeds may be the ultimate adaptive driving force that has generated the need for greater pollination efficiency.
ECOLOGICAL GENETICS OF SERPENTINE TOLERANCE IN THE MOSS, FUNARIA FLAVICANS: VARIATION WITHIN AND AMONG HAPLOID SIB FAMILIES
Authors: Shaw A. Jonathan
Published: January 2018

Many mosses occur both on and off serpentine soils, but experiments designed to test whether serpentine populations of widespread species display genetic adaptations for growth on serpentines have not been reported. Toward that end, two populations of the moss, Funaria flavicans, were grown on nutrient media varying in nickel and chromium concentration and in the ratio of magnesium to calcium. Three haploid siblings from each of five sporophytic families from the two populations were grown on five experimental media. There was no evidence that serpentine plants were more tolerant of nickel, chromium, high magnesium/calcium, or high nickel combined with high magnesium/calcium. In fact, plants from the nonserpentine population produced more protonemal growth than the serpentine plants on every medium except the control, on which plants from the two populations were indistinguishable. Large differences in nickel tolerance among haploid sib families (families of meiotic progeny derived from the same sporophyte) from the nonserpentine site provided evidence of genetic polymorphism in that population.
INTRA‐ AND INTERCLONAL COMPETITION IN THE CLEISTOGAMOUS GRASS AMPHIBROMUS SCABRIVALVIS
Authors: Cheplick Gregory P. , Salvadori Gema M.
Published: January 2018

The relationship of differences in life history traits among genotypes to competitive ability is not well known for most clonal plants. It has been hypothesized that genetically identical clones will compete more intensively than genetically distinct clones. The perennial grass Amphibromus scabrivalvis, which produces basal corms and cleistogamous seeds enclosed by leaf sheaths, exhibits pronounced clonal growth via rhizome and ramet production. In a controlled greenhouse experiment, clones of four genotypes of this species were grown under three regimes: alone in the absence of competition, paired with a clone of the same genotype (intraclonal competition), and paired with a clone of a different genotype (interclonal competition). There were differences in some biomass measures and in ramet and corm production among the four genotypes grown in the absence of competition. All genotypes showed a significant reduction in total biomass under both intra‐ and interclonal conditions, indicating that competition had occurred. For three of four genotypes, biomass allocation to corm increased under competition, while allocation to cleistogamous seeds was constant or increased slightly. Although some genotypes in specific interclonal combinations were less affected by competition than in intraclonal combinations, there was no support for the contention that the effects of competition were more intense for genetically identical clones.
TRACKING POLLEN FLOW OF SOLANUM ROSTRATUM (SOLANACEAE) USING BACKSCATTER SCANNING ELECTRON MICROSCOPY AND X‐RAY MICROANALYSIS
Authors: Wolfe Andrea D. , Estes James R. , Chissoe William F.
Published: January 2018

A technique using micronized metal powders was developed for both general labeling of pollen and marking of individual pollen grains. After labeling, pollen flow is analyzed by the use of backscatter scanning electron microscopy and X‐ray microanalysis. To test the efficiency and efficacy of the technique, we assessed differences in pollen distribution in Solanum rostratum, an enantiostylous species with dimorphic anthers which are putatively feeding and pollinating anthers. Pollen from each set of anthers was labeled using different micronized metal powders. We could not confirm the differentiation of functional anthers in S. rostratum. This technique provides an efficient and convenient method for tracking pollen movement within and between flowers, and anthers within a single blossom can be differentially marked.
CLONAL INTEGRATION: NUTRIENT SHARING BETWEEN SISTER RAMETS OF SOLIDAGO ALTISSIMA (COMPOSITAE)
Authors: Abrahamson Warren G. , Anderson Stephen S. , McCrea Kenneth D.
Published: January 2018

To test whether sharing of resources occurs among connected ramets of the tall goldenrod, Solidago altissima, we examined the extent of clonal integration for nutrients. In a greenhouse experiment, two‐ramet clones were grown in a triad of connected pots so that nutrients could be supplied to either sister ramet or to their old rhizome (mother rhizome). Mother rhizomes and their associated roots shared nutrients with daughter ramets; however, any nutrient sharing that occurred between sister ramets was too little to significantly affect their growth. In addition, sister ramets not only competed for nutrients through parental connections, but larger ramets inhibited the growth of smaller ramets. We suggest that, for tall goldenrod, a clonal growth strategy in which nutrients are not shared among sister ramets may increase genet fitness by reducing the rhizome production of ramets in poor‐nutrient microsites. Consequently, the genet would produce relatively fewer ramets in unfertile areas and make better use of heterogeneous nutrient resources.
ACROPETAL LEAF DIFFERENTIATION IN QUERCUS RUBRA (FAGACEAE)
Authors: Tomlinson P. T. , Dickson R. E. , Isebrands J. G.
Published: January 2018

Northern red oak (Quercus rubra L.) leaves were shown to mature progressively from base to tip of the lamina based on studies of growth rates, anatomical differentiation, and 14C‐transport. Lamina expansion in both length and width ceased in the basal quarter of the leaf before the apical quarter. Cell expansion and tissue differentiation were more advanced at the base than at the tip of leaves at 10%–20% of full expansion. Physiological data supported the morphological and anatomical data. Sink activity was examined by following the distribution of 14C imported into sink leaves with direct vascular connections to the source leaf to assure uniform assimilate supply to the sink leaves. Leaves approximately 50% of full expansion imported five to seven times more l4C‐assimilates into the tip than into the base of the leaf, consistent with continued sink activity in the leaf tip after import by the leaf base has ceased. Transport of 14C from portions of the leaf, indicating source activity, occurred first in the basal portion of the lamina. The base functioned as a source at approximately 40% of full expansion; the tip, at approximately 60%. Thus, northern red oak displays an acropetal pattern of leaf expansion and differentiation, unlike the more typical pattern of basipetal leaf development defined in many other dicotyledonous genera with simple leaves.
OWNBEY'S TRAGOPOGONS: 40 YEARS LATER
Authors: Novak Stephen J. , Soltis Douglas E. , Soltis Pamela S.
Published: January 2018

Two of the classic examples of recent allopolyploid speciation are Tragopogon mirus and T. miscellus. Previous studies have documented that both allotetraploids originated within the past 50–60 years; the diploid parents of T. minis are T. dubius and T. porrifolius; those of T. miscellus are T. dubius and T. pratensis. It has now been 40 years since these allotetraploids were first described by Ownbey in 1950. To assess whether population size (the absolute number of plants) and population number of these species have changed during the past 40 years, we determined their distribution and numbers in the Palouse region of eastern Washington and northern Idaho in the spring of 1990. We visited 90 localities, 60 in Washington and 30 in Idaho. Tragopogon minis is found in nine locations, with eight of these sites located in eastern Whitman County, Washington. Tragopogon miscellus is much more widespread, occurring in 38 of 90 locations. The latter species is now one of the most common weeds in the vicinity of Spokane, Washington. Comparison of the current distributions of these species with historical records indicates that both allotetraploids, especially T. miscellus, have increased substantially in both geographic range and numbers. These Tragopogon species offer an excellent model system for testing questions concerning the ecology and population biology of recently derived allotetraploid species and their diploid progenitors.
FLORAL INITIATION AND EARLY DEVELOPMENT IN ERIGERON PHILADELPHICUS (ASTERACEAE)
Authors: Harris Elizabeth M. , Tucker Shirley C. , Urbatsch Lowell E.
Published: January 2018

The order of floral initiation and subsequent organogeny of Erigeron philadelphicus L. (Asteraceae: Astereae) was found to deviate from the acropetal pattern generally reported for the Asteraceae. Light micrographs show periclinal divisions in the first, second, and deeper subsurface layers of cells on the flanks of the inflorescence apex as the earliest evidence of floral initiation. Scanning electron microscope micrographs indicate that the disk flowers appear first and arise as small protuberances approximately one‐third of the way up the previously and undifferentiated highly convex inflorescence apex. A succession of disk flowers arises acropetally in a complex anthotaxy characterized by about 21 dextrorse and 12–15 sinistrorse parastichies (although this pattern is obscured at the apex). After one to three disk flowers have been initiated in each parastichy, the first ray flower initials can be seen to initiate in sites proximal to the oldest and largest disk flowers. Additional ray flowers then initiate basipetally following the dextrorse parastichies established by the disk flowers. Overall floral initiation on the inflorescence apex proceeds acropetally for the disk flowers and basipetally for the ray flowers until the available space is filled. Floral development adheres to the same plan—proceeding bidirectionally on the inflorescence meristem with the oldest and most complete flowers of both types located on the equator established at initiation.