bluuebunny/crossref_metadata_2025 huggingface dataset:
BOTANICAL AFFINITIES OF SOME TRIPROJECTACITES FOSSIL POLLEN
Authors: Farabee Michael J.
Published: January 2018

During Late Cretaceous to Oligocene times, fossil pollen of the Triprojectacites group (also known as Aquilapolles or triprojectates), comprised a temporally and environmentally distinctive element of palynofloras in eastern Asia and western North America. Several species of this group serve as biostratigraphic index fossils for this interval. Using electron microscope and numerical analyses, primarily of North American triprojectate pollen, it is possible to recognize the presence of three distinct subgroups. One group, corresponding to the fossil genus Mancicorpus, has no morphologically close modern representative. Characters resembling those in Santalaceae (Santalales, Rosidae) occur in the second group, which is represented by a previously underscribed fossil triprojectate genus. The third group contains retipilate, isopolar pollen and strioreticulate, isopolar pollen. Forms exhibiting the latter morphology are commonly assigned to the genus Integricorpus, while the retipilate morphology characterizes another underscribed genus. This third group may have some phylogenetic connection to Apiaceae (Apiales, Asteridae). Pollen of some other extant families exhibits triprojectate features, although no close fossil representative can be presently identified. The triprojectate morphology is thus interpreted in modern and fossil forms as resulting from convergence rather than close phylogenetic relationships at the group level.
BIOMECHANICS OF CLADODES AND CLADODE‐CLADODE JUNCTIONS FOR OPUNTIA FICUS‐INDICA (CACTACEAE)
Authors: Nobel Park S. , Meyer Richard W.
Published: January 2018

Shoots of Opuntia ficus‐indica (L.) Miller consist of a sequence of flattened stem segments (cladodes) in contact over only a small portion of their periphery. The maximum angular deflection for an upper terminal cladode under a weight equal to its own fresh mass applied perpendicular to its face increased from 5° to 9° as cladode length increased from 20 cm to 60 cm, consistent with an increase in mass proportional to length2.83. Just over half of the angular deflection of an upper cladode represented flexure of the cladode‐cladode junction; the angular deflections averaged fourfold more for mass loadings perpendicular to the cladode face compared with those parallel to it. Compared with such static loading by mass, dynamic loading by wind for a 31‐cm‐long cladode led to a maximum angular deflection of only 0.13° at a wind speed of 1 m sec−1 and 2.3° at 10 m sec−1. Drought caused the angular deflections to increase 9% for 21‐cm‐long cladodes over a 90‐day period and to decrease 45% for 44‐cm‐long cladodes. Increases in stem temperature from 0 C to 20 C increased angular deflections of a 27‐cm‐long cladode about 10%, with little further increase up to 50 C. Even though the cladodes were thin compared with stems of many perennials and the cladode‐cladode junction comprised only about 3.5% of their peripheral area, the shoots of O. ficus‐indica proved to be quite rigid, as angular deflections of cladodes were only slightly influenced by temperature and wind, were not markedly enhanced by drought, and were less than 10° under loading by a cladode's mass.
SECONDARY PULVINUS OF ROBINIA PSEUDOACACIA (LEGUMINOSAE): STRUCTURAL AND ULTRASTRUCTURAL FEATURES
Authors: Moysset Luisa , Simón Esther
Published: January 2018

The structure of the secondary pulvinus of Robinia pseudoacacia has been examined together with ultrastructural features of motor cells both in open and closed pulvini, to identify ultrastructural changes associated with leaflet movement. Pulvini have a central vascular core bordered by thick‐walled collenchyma cells, which in turn are surrounded by several layers of cortical parenchyma cells. Cortical motor cells exhibit ultrastructural features similar to those reported in homologous cells of other pulvini. The vacuolar compartment contains two kinds of vacuoles: nontannin vacuoles, which change both in number and size during leaflet movement, and tannin vacuoles, which may act as an ion reservoir. No differences in wall thickness were found between flexor and extensor motor cells. Thick walls of collenchyma cells show numerous pits with plasmodesmata through which the phloem parenchyma cells and the inner cortical motor cells are connected. Tannin vacuoles and calcium oxalate crystals are common inclusions of phloem parenchyma cells. The tissue arrangement and the occurrence of pits with plasmodesmata in the central cylinder cells provide evidence of symplastic continuity through the central cylinder between the extensor and flexor regions of the motor organs. The greater amplitude of Robinia leaflet movements may be related to the extension of motor regions, the scarcity of lignification in the central vascular core, and the thin flexor walls.
CYTOLOGICAL BASIS FOR CYTOPLASMIC INHERITANCE IN PSEUDOTSUGA MENZIESII. II. FERTILIZATION AND PROEMBRYO DEVELOPMENT
Authors: Owens John N. , Morris Sheila J.
Published: January 2018

Douglas fir (Pseudotsuga menziesii [Mirb.] Franco) ovules were used to study male gamete formation, insemination of the egg, and free nuclear and cellular proembryo development. Two male nuclei form as the pollen tube either reaches the megaspore wall or as it enters the archegonial chamber. No cell wall separates them. They are contained within the body‐cell cytoplasm. A narrow extension of the pollen tube separates the neck cells and penetrates the ventral canal cell. The pollen tube then releases its contents into the egg cytoplasm. The two male gametes and a cluster of paternal organelles (plastids and mitochondria) migrate within the remains of the body‐cell cytoplasm toward the egg nucleus. Microtubules are associated with this complex. The leading male gamete fuses with the egg nucleus. The zygote nucleus undergoes free nuclear division, but the cluster of paternal organelles remains discrete. Free nuclei, paternal and maternal nucleoplasm, maternal perinuclear cytoplasm, and the cluster of paternal organelles migrate en masse to the chalazal end of the archegonium. There, paternal and maternal organelles intermingle to form the neocytoplasm, the nuclei divide, and a 12‐cell proembryo is formed. The importance of male nuclei or cells, the perinuclear zone, and large inclusions in cytoplasmic inheritance are discussed in the Pinaceae and in other conifer families. This completes a two‐part study to determine the fate of paternal and maternal plastids and mitochondria during gamete formation, fertilization, and proembryo development in Douglas fir.
A NEW BASIDIOMYCETOUS SEPTAL TYPE: THE MULTIPERFORATE SEPTUM IN KRIEGERIA ERIOPHORI
Authors: Doubles James C. , McLaughlin David J.
Published: January 2018

Septa from metabasidia and clamp connections of the heterobasidiomycetous sedge parasite Kriegeria eriophori were studied with light and electron microscopy. Septa from clamp connections subtending probasidia were reconstructed from serial sections. Septa at clamp connections are perforated by multiple, simple pores, while metabasidial septa possess single, central swellings which probably represent pores occluded by wall material. The occurrence of multiperforate septa in the fungi is reviewed. The septal morphology of K. eriophori is compared to that of simple‐septate heterobasidiomycetes, and the systematic and functional implications are discussed.
EFFECT OF MALE POLLEN DONOR AND FEMALE SEED PARENT ON ALLOCATION OF RESOURCES TO DEVELOPING SEEDS AND FRUIT IN CHAMAECRISTA FASCICULATA (LEGUMINOSAE)
Authors: Fenster Charles B.
Published: January 2018

In Chamaecrista fasciculata, fruit abortion levels are high and seed mass is highly variable, necessary preconditions for differential resource allocation of the female to seed and fruit sired by different males. This study investigated the relative role of pollen donor and seed parent on the allocation of resouces to developing seed and fruit, and assessed the role of genetic relatedness in contributing to any observed paternal effect in C. fasciculata. In addition, pollen donor effects were contrasted to within‐seed parent sources of variation in resource allocation due to pollination date and ovule position in the pod. Plants collected from the field were brought to a greenhouse where single‐donor crosses were conducted controlling for pollen donor source and interplant distance, a measure of genetic relatedness. Seed mass, number of seed/fruit, fruit maturation time, and fruit abortion rate were measured as indicators of resource allocation to developing seed and fruit. Variation in resource allocation was largely determined by the seed parent. Pollen donor effects were limited to differences between self vs. non‐self pollinations, suggesting that inbreeding depression following mating events between related individuals is the source of any variation among pollen donors on differential resource allocation to developing seed and fruit. Once the effect of inbreeding was removed, however, pollination date and ovule position played larger roles than pollen source. Since there was no detectable variation among male pollen donors in their ability to accrue resources from the female seed parent apart from inbreeding effects, it is concluded that the opportunity for postzygotic mate choice is limited in C. fasciculata.
OUTCROSSING IN THE WEED, SOLANUM PTYCANTHUM (SOLANACEAE): A COMPARISON OF AGRESTAL AND RUDERAL POPULATIONS
Authors: Hermanutz Luise
Published: January 2018

Levels of outcrossing, using a Pgm polymorphism, were estimated for individuals from ruderal and agrestal populations of the predominantly monomorphic weed Solanum ptycanthum, at the northern edge of its range, and compared to agrestal populations sampled from the southern portion of its distribution. Individuals were grown in agricultural habitats in Ontario. Outcrossing estimates of the northern agrestals were very low (< 3%) and did not differ from ruderal estimates. Southern agrestals exhibited much higher outcrossing rates (10%–17%). Of the floral traits measured, degree of stigma exsertion and style position showed interpopulation variation and correlated with outcrossing rate. Outcrossing in northern individuals was largely precluded by the complete overlap in female and male functions and stigmatic surfaces that were in direct contact with anther sacs as the flower opened. The observed flexibility in mating system may have played an important role in colonization success of 5. ptycanthum.
VERY LOW GENETIC HETEROZYGOSITIES IN SEXUAL AND AGAMOSPERMOUS POPULATIONS OF EUPATORIUM ALTISSIMUM (ASTERACEAE)
Authors: Yahara Tetsukazu , Ito Motomi , Watanabe Kuniaki , Crawford Daniel J.
Published: January 2018

An electrophoretic study revealed very low genetic heterozygosities for both sexual and agamospermous populations of Eupatorium altissimum in eastern North America. Low heterozygosity or gene diversity (HT = 0.03) can be explained by the small sizes of the extant sexual populations, estimated to be on the order of 104. There was no substantial difference in observed heterozygosity between sexual and agamospermous races. This result shows that a higher level of heterozygosity is not a prerequisite for the evolution of agamospermous races from the sexual ancestor.
TEMPORAL VARIATION OF FLOWER AND FRUIT SIZE IN RELATION TO SEED YIELD IN CELANDINE POPPY (CHELIDONIUM MAJUS; PAPAVERACEAE)
Authors: Kang Hyesoon , Primack Richard B.
Published: January 2018

Ecological and evolutionary studies typically consider variation in single reproductive characters in isolation, without considering how they might be correlated with other reproductive and vegetative characters. In our study, we examined temporal patterns of variation and correlation in flower diameter and fruit length during a reproductive phase in two Massachusetts populations of the herb, Chelidonium majus. We also examined the relationships of such variation to measurements of seed yield components (mean seed weight and number per fruit) and aspects of plant vegetative size. Most of the variation in the sizes of reproductive characters occurred within individual plants, instead of among plants or between populations. Flower and fruit sizes as well as seed number per fruit declined significantly during the season in both populations. Only mean seed size per fruit was relatively stable for individual plants in both populations. Conserving resources by a gradual reduction in the size of reproductive characters over the season may be a strategy for maternal plants to continue seed production. The strong, persistent patterns of correlation between certain characters, such as flower and fruit size, in spite of extensive phenotypic plasticity, was interpreted as indirect evidence for developmental correlation. Furthermore, vegetatively larger plants produced not only more flowers and fruits, but also consistently larger flowers and fruits. The results emphasize that variation in fitness characters, such as seed size and number, should not be viewed in isolation from vegetative characters, flower, and fruit sizes in ecological and evolutionary studies, if the goal is to understand the mechanisms of natural selection in wild populations.
RELATIVE GROWTH RATES OF VINES AND SHRUBS OF WESTERN POISON OAK, TOXICODENDRON DIVERSILOBUM (ANACARDIACEAE)
Authors: Gartner Barbara L.
Published: January 2018

Because of the different mechanical constraints on vines and self‐supporting plants, vines are thought to differ from trees and shrubs in a variety of their growth characteristics. I tested the hypotheses that vines grow faster than shrubs and that supported shoots have delayed leaf expansion relative to stem elongation, using western poison oak, Toxicodendron diversilobum (T. & G.) Greene, a plant that grows as a vine when externally supported but otherwise as a shrub. In the field, supported shoots (vines) had significantly higher aboveground biomass and relative growth rates than did their paired unsupported shoots (shrubs) growing nearby. This was not due to differences in leaf phenology, but may have resulted from vines growing into more favorable habitats for growth. In contrast, whereas 2‐yr‐old cloned plants in a common garden differed in their stem and internode lengths, they had the same aboveground dry weight, proportion of dry weight that was leaf, and relative rate of increase in primary stem length whether grown with stakes (vines) or without stakes (shrubs). These results suggest that there is no inherent requirement of vines to grow faster than shrubs. As hypothesized, leaf elongation was more delayed relative to stem elongation in staked than unstaked individuals in 19 paired plants (each pair cloned from a different source plant). Thus, physical cues resulting from the presence of support can alter the plant's spatial and temporal patterns of development, but do not necessarily dictate the quantity of biomass that will be produced.
POLLEN MORPHOLOGY AND ULTRASTRUCTURE OF THE CABOMBACEAE: CORRELATIONS WITH POLLINATION BIOLOGY
Authors: Osborn Jeffrey M. , Taylor Thomas N. , Schneider Edward L.
Published: January 2018

Of all species comprising the two genera of the Cabombaceae, only Brasenia schreberi J. F. Gmel. and Cabomba caroliniana Gray have been critically investigated with regard to their pollination biology. Brasenia schreberi has been shown to be anemophilous, while C. caroliniana has an entomophilous (myophilous) pollination syndrome. In the present paper, a number of pollen and pollen‐related characters, including pollen size, shape, quantity, terminal settling velocity, pollen‐ovule ratios, and overall exine architecture of B. schreberi and C. caroliniana are evaluated. Pollen from both species is elliptic, monosulcate, and has a tectate‐columellate sporoderm with supratectal surface ornamentation. Grains of B. schreberi are small, produced in copious amounts, and settle relatively slowly. Flowers of this species have large pollen‐ovule ratios. The exine of B. schreberi pollen is scabrate, relatively thin, has a uniformly thick sexine composed of a two‐zoned (homogeneous/granular) tectum and distinct columellae, and a homogeneous nexine. Pollen of C. caroliniana is relatively large, produced in small quantities, and has a rapid terminal settling velocity. Flowers exhibit small pollen‐ovule ratios. Exine organization of C. caroliniana pollen is typically two times thicker than that of B. schreberi; ornamentation is striate. Nonapertural sexine regions have a thick tectum and well‐defined columellae, with both sexine components traversed by a dense system of channels. The nexine is relatively thin. All of the palynological characters examined correlate well with the anemophilous and entomophilous syndromes of B. schreberi and C. caroliniana, respectively. Moreover, several other parameters of exine ultrastructure from each species exhibit positive correlations with the respective pollination mechanisms, including: tectum thickness, columellae diameter, tectum‐nexine ratios, and the consistency, distribution, and total amount of pollenkitt present. Overall exine ultrastructure is also discussed from a historical perspective as well as with respect to its phylogenetic significance.
NUCLEIC ACID AND PROTEIN SYNTHESIS DURING LATERAL ROOT INITIATION IN MARSILEA QUADRIFOLIA (MARSILEACEAE)
Authors: Lin Bai‐Ling , Raghavan V.
Published: January 2018

The pattern of DNA, RNA, and protein synthesis during lateral root initiation in Marsilea quadrifolia L. was monitored by autoradiography of incorporation of 3H‐thymidine, 3H‐uridine, and 3H‐leucine, respectively. DNA synthesis was associated with the enlargement of the lateral root initial prior to its division. Consistent with histological studies, derivatives of the lateral root initial as well as the cells of the adjacent inner cortex and pericycle of the parent root also continued to synthesize DNA. RNA and protein synthetic activities were found to be higher in the lateral root initials than in the endodermal initials of the same longitudinal layer. The data suggest a role for nucleic acid and protein synthesis during cytodifferentiation of a potential endodermal cell into a lateral root initial.
ALLOCATION OF REPRODUCTIVE RESOURCES WITHIN AND AMONG INFLORESCENCES OF LAVANDULA STOECHAS (LAMIACEAE)
Authors: Herrera Javier
Published: January 2018

Patterns of fruit set were studied in Lavandula stoechas, a Mediterranean shrub commonly occurring in southern Spain. The small, hermaphroditic flowers of this shrub are aggregated into dense, headlike inflorescences and exhibit extensive variations in fecundity. It was shown that as the number of developing fruits in the inflorescence increased, the probability of a flower setting fruit, the size of seeds, and their germinability decreased, most likely because of strong within‐inflorescence resource limitation. An experiment was designed to ascertain whether increased fertility in late‐opening flowers could be induced through reallocation of reproductive resources between different inflorescences. The experiment consisted of removing half of the inflorescence buds from a set of plants and comparing their fecundity with that of intact individuals. Thinning did not increase the proportion of flowers setting fruit which, in fact, was slightly lower than that of intact individuals (probably due to some reduction of floral display brought about by thinning). Although treated plants produced heavier seeds than controls, results suggest that inflorescences of L. stoechas behave as autonomous modules among which resources cannot be reallocated. Predispersal seed predation by insects accounted on average for a 31% reduction in fruit set. Predation was found to be nonrandomly distributed within inflorescences, with most damage concentrated on late fruits (i.e., those with smaller and less germinable seeds).
PROXIMATE AND ULTIMATE SOURCES OF WITHIN‐INDIVIDUAL VARIATION IN SEED MASS IN PRUNELLA VULGARIS (LAMIACEAE)
Authors: Winn Alice A.
Published: January 2018

Substantial variation in seed mass within individual seed parents is at odds with predictions of models for the evolution of optimum offspring size and with empirical observations of directional selection on seed mass. To elucidate the ultimate causes of this variation, I examined several proximal sources of within‐individual variation in seed mass in the perennial herb Prunella vulgaris. Position of inflorescence, position of flower within an inflorescence, date of anthesis, and number of seeds produced per flower all explained some within‐individual variation in seed mass. Hand pollination in the field failed to reveal any effect of pollen source (self pollen or outcross pollen) on seed mass. My results, in conjunction with those from studies of selection on seed mass in P. vulgaris, do not support hypotheses that within‐individual variation in seed mass is favored by the pattern of natural selection on seed mass. Rather, the results suggest that seed parents are not capable of producing a uniform seed crop in the face of changes in resource availability in the course of a season. The inability to produce a uniform seed crop may persist because of selection for variability in traits correlated with seed mass or because of a true constraint on the evolution of uniform offspring size.
SEED DYNAMICS OF ABIES BALSAMEA AND ACER SACCHARUM IN A DECIDUOUS FOREST OF NORTHEASTERN NORTH AMERICA
Authors: Houle Gilles , Payette Serge
Published: January 2018

We studied the seed dynamics of Abies balsamea and Acer saccharum in a sugar maple‐yellow birch forest of Québec, Canada. Seed rain was censused every week from spring to autumn in 1988 and 1989. The soil seed bank was sampled four times during the 1988 growing season. Abies seed rain varied significantly between 1988 and 1989. A total of 92.5 ± 7.0 seeds nr‐2 (mean ± 1 SE) were produced in 1988; 1989 seed production was null. Seed viability in 1988 averaged 31.5%. Dispersal during the winter period accounted for ca. 22% of the annual seed crop. The spatial dispersion pattern of the seed rain was contagious for the autumn period, but was not significantly different from random for the winter period. There was only a weak relationship in the spatial distribution of the seed rain between the autumn and winter periods. Abies did not maintain a persistent seed bank on the site; viable seeds were present on the soil only after seed dispersal had started. Postdispersal seed mortality was relatively high, ca. 70%. Acer seed rain started soon after the flowering period, but consisted at that time only of aborted, underdeveloped samaras. Viable seeds were disseminated from September through early winter. Dispersal during the autumn accounted for ca. 98% of the annual seed crop. There were significant differences between seed rain abundance of 1988 and that of 1989 (118.1 ± 9.5 samaras m‐2 and 158.9 ± 16.3 samaras m‐2 in 1988 and in 1989, respectively). Seed viability also varied significantly between the 2 years, i.e., 19% in 1988 and 5% in 1989. For both 1988 and 1989, samaras were contagiously dispersed over the site. There was a significant positive relationship between the spatial distribution of the seed rain in 1988 and that in 1989. Seed rain abundance was high mainly in the proximity of mature Acer trees. As for Abies, Acer did not maintain a persistent seed bank in the soil; viable seeds were present only in the autumn seed bank sampling, after seed fall had started. Postdispersal seed mortality was relatively low, i.e., 20%. Abies and Acer are quite similar in their regenerative traits, and these contrast sharply with those of Betula alleghaniensis, a regular member of this forest community. Differences in regenerative traits may contribute to the coexistence of these tree species considering the gap regime of the system studied.
PRIMARY AND SECONDARY EFFECTS OF WATER CONTENT ON THE SPECTRAL REFLECTANCE OF LEAVES
Authors: Carter Gregory A.
Published: January 2018

Leaves of six species selected to represent a broad range in internal structure were collected in the field and studied in the laboratory to determine primary and secondary effects of water content on leaf spectral reflectance. Primary effects were those that resulted solely from the radiative properties of water. Secondary effects were those that could not be explained solely by these properties. Decreased leaf water content generally increased reflectance throughout the 400‐2,500‐nm wavelength range. For the aquatics Eichhornia crassippes and Nuphar luteum, the broadleaved trees Liquidambar styraciflua and Magnolia grandiflora, the cane‐grass Arundinaria tecta, and the needle‐leaved Pinus taeda, the sensitivity of reflectance to water content was greatest in the water absorption bands near 1,450, 1,940, and 2,500 nm. Sensitivity maxima occurred also between 400 and 720 nm, indicating secondary effects that resulted from decreased absorption by pigments. Secondary effects of water content on reflectance that were largely wavelength‐independent, together with any wavelength‐independent effects of leaf internal structure, were far less significant than primary and secondary effects resulting from decreased absorption by water and pigments, respectively.
ISOZYME DIVERGENCE BETWEEN EASTERN ASIAN, NORTH AMERICAN, AND TURKISH SPECIES OF LIQUIDAMBAR (HAMAMELIDACEAE)
Authors: Hoey Margaret T. , Parks Clifford R.
Published: January 2018

The deciduous woody genus Liquidambar has four morphologically similar species in eastern and western Asia, eastern North America, and Central America. Liquidambar styraciflua is found in the eastern United States and Central America, L. orientalis is native only to southwest Turkey, and L. formosana and L. acalycina occur in eastern Asia. This genus is one of many that contributes to the floristic similarities observed between these different regions. Allelic variation was scored at 22 isozyme loci from 41 populations. The level of genetic divergence between species on different continents is high. Nei's genetic identity was 0.431 between L. formosana and L. styraciflua, 0.485 between L. acalycina and L. styraciflua, 0.512 between L. orientalis and L. styraciflua, 0.256 between L. formosana and L. orientalis, and 0.305 between L. acalycina and L. orientalis. Estimates of time of divergence from the isozyme data suggest that the current species diverged before or during the Miocene. The pattern of relationships portrayed by the isozyme data suggest a longer period of separation between the eastern and western Asian forms of this genus. In addition, the eastern North American and Turkish species appear to be the most closely related intercontinental pair of species providing evidence for a North Atlantic land bridge as late as the Miocene. It would appear, therefore, that the North American populations were in contact with the Asian populations over the North Pacific and North Atlantic possibly as late as the Miocene, but that the separation between the two Asian populations occurred much earlier. The time of divergence as measured from the isozyme data correlates with an independent assessment of the origin of these disjuncts as determined from the fossil record.
THE ECOLOGICAL IMPACT OF ALLELOPATHY IN AILANTHUS ALTISSIMA (SIMAROUBACEAE)
Authors: Lawrence Jeffrey G. , Colwell Alison , Sexton Owen J.
Published: January 2018

Compounds inhibitory to the growth of neighboring plant species were found in significant concentrations in the leaves and stems of young Ailanthus altissima ramets. The surrounding soil also contained appreciable concentrations of similarly acting toxins. Individuals of neighboring plant species have either incorporated active portions of inhibitory compounds or responded to Ailanthus by producing growth‐inhibiting substances. Under greenhouse conditions, individuals of neighboring plant species previously unexposed to Ailanthus in the field were found to be more susceptible to the Ailanthus toxins than individuals previously exposed. Moreover, seeds produced by unexposed populations were also more susceptible to Ailanthus toxins than seeds produced by previously exposed populations. These differences demonstrated that the allelochemicals of Ailanthus altissima exhibited a measurable impact upon neighboring plant species. Since the progeny of these populations displayed a differential response to Ailanthus toxin, this phenotypic difference between the two populations may have a heritable basis.
CONSEQUENCES OF EMERGENCE PHENOLOGY FOR REPRODUCTIVE SUCCESS IN RANUNCULUS ADONEUS (RANUNCULACEAE)
Authors: Galen Candace , Stanton Maureen L.
Published: January 2018

This study explores the effects of emergence time and reproductive phenology on seed number, seed size, and seedling survival in a population of the alpine buttercup, Ranunculus adoneus. Phenology in this snow bowl population is structured by snow depth. Plants in late melting interior portions of the bowl emerged and flowered 3 to 4 wk after those in early melting zones at the bowl perimeter during the summers of 1988 and 1989. Flowering time differences of buttercups across the bowl were consistent from one year to the next. In 1988, late flowering plants tended to set fewer seeds than early flowering ones; in 1989 no decrease in seed number accompanied flowering date. Path analysis showed that equal fecundity in early and late emerging portions of the bowl population during 1989 resulted from balancing spatial and temporal constraints on seed production. Spatial aspects of habitat quality improved toward the interior of the bowl, but temporal regimes deteriorated in these late melting sites. In both 1988 and 1989 seed size declined with delays in flowering. Path analysis of 1989 data showed that because of reduced time for seed growth, plants in late melting portions of the bowl set smaller seeds than those in earlier melting zones. Differences in seed size due to parental phenology are likely to influence fitness in snow buttercups. Under natural conditions, seedlings from large seeds (>;0.65 mg) have sixfold higher survival than do those from smaller seeds (<;0.65 mg). We conclude that seedling recruitment may be infrequent in late‐melting portions of the snow bowl due to delayed parental phenology.
EVIDENCE FOR A CLOSE RELATIONSHIP BETWEEN IOSTEPHANE AND VIGUIERA (ASTERACEAE: HELIANTHEAE)
Authors: Schilling Edward E. , Panero Jose L.
Published: January 2018

The phylogenetic relationship of Iostephane is assessed using data from morphology, flavonoid chemistry, and chloroplast DNA and nuclear ribosomal DNA restriction fragment analysis. Morphological evidence supports placement of Iostephane in subtribe Helianthinae, but fails to clarify the placement of the genus within this assemblage. Further evidence for the placement of Iostephane in subtribe Helianthinae is provided by the presence in all species of the genus of floral flavonoids of the chalcone/aurone type, which provides a distinctive trait for the subtribe within the tribe Heliantheae. Analysis of chloroplast DNA from two species of Iostephane, I. heterophylla and I. madrensis, in comparison to Viguiera and related genera indicates that the restriction site patterns with 16 enzymes for the Iostephane species are virtually identical to one another as well as to those of Viguiera sect. Maculatae. Data from restriction fragment patterns of nuclear rDNA are concordant with the results from chloroplast DNA in suggesting a direct relationship between the two groups. The close phylogenetic relationship between Iostephane and Viguiera sect. Maculatae suggested by the DNA restriction fragment data was not suggested by any other set of data.
GENETIC DIVERSITY IN THE MONOECIOUS HYDROPHILE CERATOPHYLLUM (CERATOPHYLLACEAE)
Authors: Les Donald H.
Published: January 2018

This study surveys genetic variation in two clonal, monoecious, water‐pollinated species that differ in their extent of sexuality and distributional range. Electrophoresis was used to quantify allozyme variability in 12 Wisconsin populations of the widespread Ceratophyllum demersum and the rare C. echinatum. Electrophoretic data indicate that populations of both species have low levels of sexual recombination, low levels of variation, and are structured genetically like inbreeding terrestrial plants. Ceratophyllum populations differ from “typical” clonal terrestrial plants by lower genetic diversity, lower proportions of multiclonal populations, and fewer genotypes per population. In two populations where sexual recombination is documented, heterozygosity is low with significant deficiencies. Monoecy in Ceratophyllum may be related to historical evolutionary factors, whereas vegetative reproduction has a greater influence on the genetic population structure of extant populations. The low genetic identity between C. demersum and C. echinatum supports their recognition as distinct species.
ALLYL ISOTHIOCYANATE RELEASE AND THE ALLELOPATHIC POTENTIAL OF BRASSICA NAPUS (BRASSICACEAE)
Authors: Choesin Devi N. , Boerner Ralph E. J.
Published: January 2018

The allelopathic potential of Brassica species has been attributed to release of the mustard oil glycosides which they produce in large quantities. Upon hydrolysis, these glucosinolates yield isothiocyanates, compounds with strong antibiotic properties. The objective of this study was to assess whether Brassica napus, a common and widespread crop and weed crucifer, is capable of allelopathic interference, and if so, whether its glycoside derivative, allyl isothiocyanate (AI), is capable of producing this interference. Wild type and low glucosinolate‐mutant B. napus were grown in low organic content soil under greenhouse conditions, and AI release into soil was monitored. Most plants released low levels of AI, though approximately 10% released much higher levels. Wild type plants released more AI than mutants. Growth of the target species, Medicago sativa, was not affected by additions of AI to soils at concentrations equal to the median and 95% quantile from the B. napus soils. In replacement series experiments, the two B. napus genotypes suppressed growth of M. sativa equally despite differences in AI release rate. In an intraspecific replacement series experiment, the two B. napus genotypes were equal competitors. Under our experimental conditions, B. napus showed no indication of being allelopathic, and AI concentrations typical of soils around B. napus plants did not inhibit target plants.
CUTICLE DEVELOPMENT ON GLANDULAR TRICHOMES OF CANNABIS SATIVA (CANNABACEAE)
Authors: Mahlberg Paul G. , Kim Eun‐Soo
Published: January 2018

The dermal sheath of glandular trichomes of Cannabis sativa L., consisting of cuticle and a subcuticular wall, was examined by transmission electron microscopy. Cuticle thickened selectively on the outer wall of disc cells of each trichome prior to formation of the secretory cavity, whereas thickening was less evident on the dermal cells of the bract. Membraned secretory vesicles that differ in size and appearance in the secretory cavity were the source of precursors for synthesis of cuticle. Vesicle contents, released following the degradation of the vesicle membrane upon contact with the subcuticular wall, contributed to both structured and amorphous phases of cuticle development. The structured phase was represented by deposition and thickening of cuticle at the subcuticular wall‐cuticle interface to form a thickened cuticle. In the amorphous phase precursors permeated the cuticle in a liquid state, as shown by fusion of cuticles and wax layers between contiguous glands, and may have contributed to growth in surface area of the expanding sheath. Disc cells are interpreted to control growth of secretory cavity by secretion of membraned vesicles into the cavity. The thickened cuticle, which increased eightfold in thickness during enlargement of the gland, provided structural strength for the extensive surface area of the dermal sheath. The gland of Cannabis in which vesicle contents contribute to the growth in thickness and surface area of the cuticle of the sheath is interpreted to represent a phylogenetically derived state as contrasted to secretory glands possessing only cuticle and lacking a complement of secretory vesicles.
POPULATION STRUCTURE, BIOMASS ALLOCATION, AND PHENOTYPIC PLASTICITY IN MURDANNIA KEISAK (COMMELINACEAE)
Authors: Dunn Christopher P. , Sharitz Rebecca R.
Published: January 2018

Field and glasshouse studies were used to explain differences in plant biomass, shoot length, and reproductive effort in four populations of a wetland annual herb, Murdannia keisak. Populations were chosen from continually thermally disturbed, intermittently thermally disturbed, revegetating, and undisturbed portions of a floodplain forest in South Carolina, USA. Plants in the two thermally disturbed areas were shorter, flowered earlier in the autumn, and produced more and smaller seeds than plants in revegetating and undisturbed sites. Reproductive effort was higher in populations from undisturbed and revegetating sites than in the two thermally disturbed sites. Generally, differences observed in the field were not expressed in the glasshouse plants. Glasshouse experiments suggested that most of the observed among‐population differences in size and reproductive effort in the field study were a result of a plastic response to water depth and light. The combination of field and glasshouse data showed that this wetland weed adjusts readily to newly disturbed habitats, thus spreading rapidly and maintaining local dominance.
EFFECTS OF FIRE IN TALLGRASS PRAIRIE ON GROWTH AND REPRODUCTION OF PRAIRIE CONEFLOWER (RATIBIDA COLUMNIFERA: ASTERACEAE)
Authors: Hartnett David C.
Published: January 2018

Effects of fire on growth and reproduction of the perennial forb Ratibida columnifera were studied on the Konza Prairie Research Natural Area in northeastern Kansas, USA. Populations were sampled in seven different tallgrass prairie watersheds that varied in fire frequency and in the number of years elapsed since the last fire. Plants from sites not burned for many years were 2.6 times larger and produced 50% more stems than plants from recently burned sites. Number of seeds per plant was also higher in long‐unburned sites due to greater numbers of flower heads per plant and greater numbers of achenes produced per head. Reproductive effort (ratio of inflorescence biomass to total vegetative biomass) was 33% lower in annually burned prairie than in any of the other sites. Significant differences in the relationships of inflorescence biomass to vegetative plant biomass in burned vs. unburned sites indicated that burning causes direct changes in plant reproductive effort independent from its effects on plant size. There was no clear relationship between patterns of seed production among sites and patterns of R. columnifera abundance. Ratibida columnifera responses to fire are most likely a result of changes in the relative competitive abilities of forbs and the dominant perennial grasses due to post‐fire changes in abiotic conditions rather than a result of direct effects of fire on the fate of buds and subsequent vegetative and floral development.
PATTERNS OF ALLOZYME DIVERSITY IN THE WEST INDIES CYCAD ZAMIA PUMILA (ZAMIACEAE)
Authors: Walters Terrence W. , Decker‐Walters Deena S.
Published: January 2018

The West Indies cycad, Zamia pumila, is restricted to the Greater Antilles, northern Bahama Islands, Florida, and the southeastern coast of Georgia. An electrophoretic study based on nine enzymes compared 21 accessions from throughout the range of the species. Lower levels of intrapopulation variation than those reported for ferns, other gymnosperms, and angiosperms were discovered for the two more extensively sampled populations. However, this variation was similar to that found in other island taxa and in the endemic Australian cycad, Macrozamia communis. In contrast, allozyme divergence among accessions of Z. pumila appeared relatively high, mostly as a result of rare alleles restricted in geographic distribution. The age and biogeography of Z. pumila may gave contributed to population differentiation. Also, mean number of alleles per locus was low for the species (1.75). Finally, the time‐since‐divergence value (10.8 million years ago) between Z. pumila and its closest extant relative, Z. splendens, was much smaller than the age of Z. pumila suggested by the fossil record and historical geology of the Caribbean (30–60 million years ago). Together, these data indicate that biochemical evolution within this species, and perhaps in all cycads, is slow when compared to that of noncycad seed plants.
GENETICS OF SEX EXPRESSION IN FRAG ARIA SPECIES
Authors: Ahmadi Hamid , Bringhurst Royce S.
Published: January 2018

Hermaphroditism is the normal mode of sex expression in diploid species of Fragaria (Rosaceae, 2n = 14, x = 7) with one known exception, gynodioecious F. vesca L. ssp. bracteata. The polyploid species of Fragaria are all trioecious. An extensive study involving appropriate hybridization, testcrossing, selling, and backcrossing revealed that the repression of sporangia and the inhibition of sporogenesis are controlled by a single gene (or a gene complex) with at least three alleles in the sporophytes of trioecious octoploid species (2n = 56, x = 7). A male suppressor (allele F) reduces microsporangia and represses microsporogenesis completely, but it allows normal development of the stigma, style, and ovary. A female suppressor (allele M), in the absence of modifier genes, inhibits megasporogenesis and drastically reduces the number of carpels and size of receptacles. The allele H, conferring perfect flowers at an early stage of flower organogenesis, acts as an inducer of microsporogenesis in females, but leaves both microand megasporangial development intact. At the sex locus, the F allele (femaleness) is dominant to H and M and the H allele (hermaphroditism) is dominant to M (maleness). Females are exclusively heterogametic (F/H or F/M), hermaphrodites may be homo‐ or heterogametic (H/H or H/M), and males are homogametic (M/M). The sex gene is expressed precisely in the genetic background of octoploid × diploid hybrids of Fragaria and their derivatives and in crosses with closely related hermaphroditic diploid Pontentilla glandulosa L. Gene dosage phenomena are absent. First generation progeny of colchi‐decaploids (F/F, –/–) are exclusively female, but all generations thereafter segregate in a normal diploidized manner (1:1). Application of phytohormones alters sex expression to a limited extent.
DROUGHT ACCLIMATION OF AN UNDERSTORY SHRUB (PSYCHOTRIA LIMONENSIS; RUBIACEAE) IN A SEASONALLY DRY TROPICAL FOREST IN PANAMA
Authors: Mulkey Stephen S. , Wright S. Joseph , Smith Alan P.
Published: January 2018

Physiological responses to seasonal drought were explored for Psychotria limonensis (Rubiaceae), an abundant understory shrub in a seasonally dry tropical forest in Panama. Control and irrigated plants were compared at the beginning and again at the end of the 4‐mo dry season. Stomatal conductance remained high throughout for irrigated plants, but fell to very low levels for control plants late in the dry season. Net assimilation rates under both saturating and ambient light were unaffected by irrigation. As a consequence, instantaneous water‐use efficiency (assimilation ÷ evapotranspiration), derived from gas exchange measures, and long‐term water‐use efficiency, estimated from stable carbon isotope ratios of leaf tissue, were similar for both treatments. The maintenance of high assimilation rates despite drought may be related to osmotic adjustment. Control plants had more negative osmotic potentials at full turgor and higher moduli of elasticity in the late dry season.
NONDEEP COMPLEX MORPHOPHYSIOLOGICAL DORMANCY IN SEEDS OF OSMORHIZA CLAYTONII (APIACEAE)
Authors: Baskin Jerry M. , Baskin Carol C.
Published: January 2018

Freshly matured seeds of Osmorhiza claytonii exhibit a type of morphophysiological dormancy (MPD). Under natural conditions, embryo growth begins in late September and early October and continues until mid***‐ to late February, with the peak in October and November. Most seeds germinate between mid‐February and late March. Embryos did not grow in seeds incubated for 24 weeks at 30/15 (warm stratification) or 5 C (cold stratification). However, in seeds given 12 weeks at 30/15 and then 12 weeks at 5 C, embryo length increased 1,246% while seeds were at 5 C. Zero to 7 days of warm followed by 24 weeks of cold stratification resulted in 2%–27% germination of fresh seeds, whereas 2 to 12 weeks of warm followed by 24 weeks of cold stratification resulted in 80%–98% germination. Warm plus cold stratification was required for embryo growth and germination of seeds that remained undispersed for a year in the field. GA3 was partially effective in substituting for warm stratification. The name “nondeep complex MPD” is proposed for the type of MPD found in O. claytonii and a few other species, making a total of eight types of MPD presently known.
POLLEN‐MEDIATED GENE FLOW IN CUCURBITA FOETIDISSIMA (CUCURBITACEAE)
Authors: Kohn Joshua R. , Casper Brenda B.
Published: January 2018

Pollen‐mediated gene flow along a linear series of patches of the functionally gynodioecious, bee‐pollinated Cucurbita foetidissima was assessed using electrophoretic analysis of seed allozymes. Gene flow was documented at distances up to 0.7 km. For the 13 patches examined, interpatch pollen must have sired from 0% to 48.3% (X̄ = 8.5%) of the seeds of monoecious plants (hermaphrodites). Rates of interpatch siring of seeds of pistillate plants (females) averaged 20.4% (range 8.6%‐40%) for the three patches examined. Heterogeneity among fruits in seeds sired by interpatch pollen indicates that the arrival of interpatch pollen is clumped with respect to stigmas. Within patches, plants of the same sex type usually shared identical five‐locus genotypes, suggesting that clonal propagation predominates. Since approximately 90% of seeds are sired by intrapatch pollen, seeds of monoecious plants appear to result primarily from geitonogamous (self‐) fertilization. This may help explain the existence of female plants in natural populations, since self‐fertilization has been shown to severely reduce the survival of seedlings in this species.
GENETIC DIVERSITY AND CLONAL STRUCTURE IN A COLUMNAR CACTUS, LOPHOCEREUS SCHOTTII
Authors: Parker Kathleen C. , Hamrick J. L.
Published: January 2018

In southern Arizona the columnar cactus, Lophocereus schottii, inhabits desert riparian environments. Reproduction in this part of its range is predominantly asexual and occurs by either the dispersal of stems in the immediate vicinity of parents or the long‐distance transport of detached stem pieces downstream by floodwaters. Genetic diversity and clonal structure of eight populations of L. schottii in Organ Pipe Cactus National Monument, Arizona, were examined. In all populations ramets were mapped and stem tissue from each ramet was examined electrophoretically. At the species level, 44.4% of the loci were polymorphic and the genetic diversity was 0.145. Within populations, the mean proportion of polymorphic loci and genetic diversity were 34.4% and 0.126%, respectively. Although most of the allozyme variation was within populations, appreciable heterogeneity was found among populations (GST = 0.130). Genetic and genotypic diversity was greatest in three of the four populations located in the principal area of L. schottii occurrence in the monument. Genotypic diversity was lowest in the smallest population and in the most isolated population. Ramets in all populations were spatially aggregated. Plant pairs with identical multilocus genotypes were usually ≤ 10 m apart, but some widely separated individuals had identical genotypes. Occasional long‐distance dispersal of stems and the periodic recruitment of seedlings have caused genets to intermingle, promoting outcrossing and maintaining genetic diversity.