bluuebunny/crossref_metadata_2025 huggingface dataset:
TREE SEEDLING EMERGENCE ON INTERACTIVE TEMPERATURE AND MOISTURE GRADIENTS AND IN PATCHES OF OLD‐FIELD VEGETATION
Authors: Burton Philip J. , Bazzaz F. A.
Published: January 2018

Seeds of tree species commonly invading old‐fields (Fraxinus americana, Gleditsia triacanthos, Morus rubra, Platanus occidentalis, and Prunus serotina) were germinated at eight temperatures from 5 C to 40 C, with six moisture levels (2% to 18% gravimetric moisture content) at each temperature. For most species, total seedling emergence and emergence rate exhibited approximate bivariate Gaussian response surfaces. Emergence of all species, except Gleditsia, was much more sensitive to differences in temperature than to differences in moisture. Species differed considerably in their response breadths across the interactive gradients, with moisture response bearing little relationship to temperature response.

Seeds of Acer saccharum, Crataegus mollis, Fraxinus americana, Gleditsia triacanthos, Morus rubra, and Prunus serotina were sown into old‐field vegetation patches dominated by eight different plant species, across three different soils. Acer and Morus emergence exhibited no significant differences among vegetation patches. Emergence of other tree species differed among patch types, but identity of the vegetation (often early successional) most conducive to emergence typically varied from year to year. Emergence of most species responded more strongly to vegetation than to soil series. High Fraxinus and Prunus emergence was associated with dampened temperature ranges, while high Crataegus emergence was associated with low amounts of plant litter. Despite great variability, vegetation differences can predict tree seedling emergence better than do year‐to‐year or soil differences. Extrapolations from the laboratory experiments predicted approximate levels of overall seedling emergence in the field, but prevailing temperatures and moisture differences among plant neighborhoods alone were not sufficient to explain observed differences in seedling emergence among these patches.
OSMOTIC ADJUSTMENT AND DYNAMIC CHANGES IN DISTRIBUTION OF LOW MOLECULAR WEIGHT SOLUTES BETWEEN CELLULAR COMPARTMENTS OF CARROT AND BEET ROOT CELLS EXPOSED TO SALINITY
Authors: Reuveni Moshe , Lerner Henri R. , Poljakoff‐Mayber Alexandra
Published: January 2018

Carrot cells (Daucus carota L.) in suspension culture exposed to medium containing 150 mM NaCl plasmolyzed immediately and deplasmolyzed within 35 to 40 hr. Three days after exposure to NaCl the cells resumed proliferation. Accommodation to salinity and renewal of growth was accompanied by absorption of Na+ from the external medium. On completion of deplasmolysis, K+ concentration in the cytosol doubled and Na+ concentration approximated that of K+. The vacuolar K+ concentration was practically unchanged while Na+ accumulated to a concentration double that of K+. Cl−‐ accumulation started later and eventually exceeded that of Na+ plus K+. Malate was redistributed during accommodation to salinity and eventually returned to its initial level. Amino acid content in the cytosol increased fivefold, while in the vacuole it remained unchanged. These results show that: 1) recovery from osmotic shock requires absorption of easily penetrating solute, mainly Na+; 2) distribution of solutes, absorbed or synthesized in cells exposed to salinity, is a dynamic process; 3) cells could grow and proliferate in high NaCl content in the cytosol; 4) red beet root cells grown in the presence of NaCl contain higher cytoplasmic Na+ than K+; and 5) during adjustment to salinity small spherical carrot cells survive the osmotic shock and do not show any detectable damage.
GEOGRAPHICAL VARIATION IN ASIMINA TRILOBA DUNAL (ANNONACEAE) REVEALED BY THE M13 “DNA FINGERPRINTING” PROBE
Authors: Rogstad Steven H. , Wolff Kirsten , Schaal Barbara A.
Published: January 2018

Genetic variation for variable DNA loci was investigated in Asimina triloba using the M13 “fingerprinting” probe. A survey of plants from widely separated sites across portions of the geographical range of the species showed that each site possessed a distinct set of DNA fragments. The probability of two individuals having identical fragment patterns was approximately 1/1,700 at this geographical range. Levels of variation at local sites were quite different than at a wide geographic scale. Within‐population variation ranged from moderate levels to none. The fragment profile of a fruit‐bearing tree was compared with those of nine of its offspring; all progeny were identical with the maternal parent, indicating that both the staminate and carpellate sources were homozygous at all detected loci. These results suggest that while genetic variation is detectable both among distant individuals and within some very local populations, clonal propagation and/or inbreeding have led to a lack of genetic variation in some populations of A. tribola.
TEMPERATURE‐INDUCED CAVITIES AND SPECIALIZED PARENCHYMA CELLS IN THE VASCULAR CYLINDER OF PEA ROOTS
Authors: Lu Pengzhe , Gladish Daniel , Rost Thomas L.
Published: January 2018

Pea seeds (Pisum sativum L.) of six cultivars were planted in the field, in the greenhouse, or in growth chambers, in five different media, in light or dark, and at various temperatures (10–32 C). Under all conditions above 15 C the central portion of the vascular cylinder, in all cultivars except “Ageotropum,” tended to form cavities in almost every primary root examined. These cavities then became filled by the ingrowth of specialized parenchyma cells (SP cells). The formation of cavities and SP cells was temperature dependent since the roots grown below 15 C always formed central metaxylem tracheary elements (MTEs), without cavities and SP cells. Cavities and SP cells did not form over the entire root length. When the roots were longer than 3 cm, they started to form cavities and SP cells and continued for an additional 10–30 cm. After that, late MTEs formed in the central vascular cylinder, and no cavities and SP cells occurred regardless of temperature. Within an individual root grown above 15 C, cavities and SP cells tended to form during periods of fast growth, while during periods of slow growth large central MTEs formed instead.
CHARACTERIZATION OF A NARROW HYBRID ZONE BETWEEN TWO SUBSPECIES OF BIG SAGEBRUSH (ARTEMISIA TRIDENTATA: ASTERACEAE)
Authors: Freeman D. C. , Turner W. A. , McArthur E. D. , Graham J. H.
Published: January 2018

Hybridization between Artemisia tridentata ssp. tridentata and A. t. ssp. vaseyana occurs in a narrow elevational zone along the west face and canyons of the Wasatch Mountains of Utah. Two sites in central Utah (Orem and Salt Creek) were examined. The parental taxa differ in anatomy, morphology, flavonoid and coumarin content, as well as various growth parameters. Hybrids are intermediate for the majority of traits examined, including flavonoid and coumarin composition. Multivariate statistics show that these taxa can be unambiguously identified using simple field measures of morphology. A hybrid index was constructed using principal component analyses on morphological variables.
RELATIVE ELEMENTAL RATES OF ELONGATION AND THE PROTOXYLEM‐METAXYLEM TRANSITION IN HYPOCOTYLS OF SOYBEAN SEEDLINGS
Authors: Paolillo Dominick J. , Rubin Gail
Published: January 2018

The transition from helical to reticulate wall patterns in the conducting elements of the xylem was located in etiolated soybean hypocotyls in conjunction with the distribution of elongation in the axis. The most acropetal reticulate elements are interpreted as the most acropetal metaxylem. Evidence is given that these elements experience strain as they mature. Predicted strain correlated significantly with maximum relative elemental rate of elongation (RELEL), which ranged from 0.08 to 0.12‐hr‐1. RELEL varied from 0.03 to 0.06hr‐1 at the point of transition from helical to reticulate xylem element wall patterns. Estimates of strain to be experienced in the reticulate elements varied from 0.11 to 0.13 in untransplanted plants and from 0.04 to 0.11 in plants transplanted to the same, fully watered medium. Transplanting suppressed elongation in the region of maximum RELEL for ca. 12 hr and caused an upward migration of the region of depressed rates on the outside of the axis that accounts for hook‐opening. Attention is called to the fact that this region of depressed growth corresponds with the onset of transverse enlargement of the hypocotyl axis.
DISTANCE BETWEEN MATES AFFECTS SEEDLING CHARACTERS IN A POPULATION OF IMPATIENS CAPENSIS (BALSAMINACEAE)
Authors: McCall Claire , Mitchell‐Olds Tom , Waller Donald M.
Published: January 2018

We tested for the presence of an optimal outcrossing distance in a population of Impatiens capensis, an annual herb that possesses a mixed mating system, by measuring fitness components for offspring of parents that were separated by distances of 2, 10, or 50 m. Heavier seed weights and later seed maturation enhanced probabilities of emergence and subsequent survival, but emergence and survival were unaffected by outcrossing distance. Path analysis showed that most characteristics of seeds and seedlings were positively correlated. Effects of maternal family were strong through the first month of growth. Analyses of covariance reveal that, as anticipated, the effects of maternal family, seed weight, and seed maturation date declined over time. Seeds that were produced late in the season were heavier than early seeds, and late seeds germinated at later dates than early seeds. Surprisingly, although late germination dates were associated with taller plants after 1 and 3 months of growth, late germination resulted in lighter dry weights at maturity. The distance between parents had a negative direct effect on seed weight but a positive effect on height after 1 month. Height at 1 month responded positively to outcrossing distance and negatively to the square of distance when seed weight, collection date, and maternal family were held constant. This implies an optimal outcrossing distance for height at 1 month, which we estimate as 29 m using a quadratic procedure. However, path analysis suggests that the apparent optimum is due to a negative correlation between the interparent distance and seed weight.
DISTINGUISHING PLANT TISSUES WITH MAGNETIC RESONANCE MICROSCOPY
Authors: Veres John S. , Cofer Gary P. , Johnson G. Allan
Published: January 2018

Using magnetic resonance microscopy at 7 Tesla, spin‐lattice relaxation times (Tl), spinspin relaxation times (T2), and spin densities (N(H)) of live squash stem tissues were measured in order to gain an understanding of live tissue water relations and to improve imaging protocols that allow the clear distinction of tissues. T1 and N(H) differences among tissues were found to be much greater than T2 differences. Most tissues can be distinguished with high resolution T1 weighted images. Sclerenchyma and vessel elements are more easily seen with N(H) weighted images because of the relatively low water content of sclerenchyma and high water content of vessel elements. This work demonstrates further improvements in the ability of MR microscopy to distinguish tissues and individual cells and also to make measurements regarding water status at the tissue and cellular level of live plants in a nondestructive manner.
IMPORTANCE OF TIME OF GERMINATION AND SOIL DEPTH ON GROWTH OF PROSOPIS GLANDULOSA (LEGUMINOSAE) SEEDLINGS IN THE PRESENCE OF A C4 GRASS
Authors: Bush J. K. , Van Auken O. W.
Published: January 2018

In an investigation of the causes of the invasion of woody plants into grasslands, competition between seedlings of Prosopis glandulosa Torr. and Bouteloua curtipendula (Michx.) Torr. was examined. Introduction of P. glandulosa into a B. curtipendula neighborhood significantly reduced P. glandulosa dry mass when compared to P. glandulosa growth alone. The greater the time interval from P. glandulosa germination to addition of B. curtipendula, the less interference the grass had on woody plant growth. Reciprocally, the greater the time interval from B. curtipendula germination to addition of P. glandulosa, the more interference the grass had on woody plant growth. Prosopis glandulosa belowground dry mass was <0.02 g (all in the upper 30 cm of soil) when planted after B. curtipendula at any soil depth, but if planted alone its root dry mass ranged from 2 to 8 g depending on depth. Prosopis glandulosa seedling dry mass increased linearly with soil depth, while B. curtipendula dry mass reached a plateau. In general, belowground dry mass of P. glandulosa was distributed throughout the soil depth examined (decreasing with depth), while 80% of B. curtipendula dry mass was found in the upper 30 cm of soil, suggesting a partitioning of soil resources. Data suggest that P. glandulosa and perhaps other shade‐intolerant woody species that establish in grasslands do so in disturbances or vegetation gaps. Gaps may close, but by this time woody plant roots are below grass roots, thus partitioning soil resources and reducing interspecific competition.
MULTIPLE PATERNITY AND SELF‐FERTILIZATION IN RELATION TO FLORAL AGE IN MIMULUS GUTTATUS (SCROPHULARIACEAE)
Authors: Dudash Michele R. , Ritland Kermit
Published: January 2018

To gain some understanding of the mechanisms responsible for the intermediate levels of both multiple paternity and selfing observed previously in the common monkeyflower, Mimulus guttatus, we performed a field experiment to assess the role of 1) multiple paternity through sequential pollinator visits and 2) selfing through corolla abscission. In M. guttatus, flowers remain open for several days; then, in the process of corolla abscission anthers drag past the stigma. We predicted that multiple visitation by pollinators over this period should increase the degree of multiple paternity of sibling arrays, and that corolla dragging may be the primary cause of the observed selfing. In three northern California populations corollas were removed after being open for 1 day (preventing further mating), and the type of matings resulting was compared to matings from adjacent flowers with undisturbed corollas. On average, seed set was twice as great in flowers with unmanipulated corollas, indicating that about half of all matings in the lifespan of a M. guttatus flower occur after 1 day. Pollen supplementation revealed that pollen was limiting in one population. Electrophoretic assay of progeny showed multiple paternity was greater in unmanipulated flowers in the two populations that were not pollen limited, suggesting that sequential pollination may be an important source of multiple paternity. However, no difference was detected in the selfing rate between the two treatments, suggesting that corolla dragging was not a source of selfing even under pollen‐limited conditions.
ELECTROPHORETIC AND CYTOGENETIC EVIDENCE FOR ALLOPOLYPLOID ORIGIN OF MARSHALLIA MOHRII (ASTERACEAE)
Authors: Watson Linda E. , Elisens Wayne J. , Estes James R.
Published: January 2018

Marshallia mohrii is a tetraploid species, 2n = 4x = 36, with approximately 17% of its pollen mother cells exhibiting a single quadrivalent at diakinesis of Meiosis I. The species is morphologically most similar to M. grandiflora, a member of the Grandiflora complex along with M. mohrii and M. trinervia. These data led to the preliminary hypothesis that M. mohrii originated by autopolyploidy. However, we rejected the autopolyploid hypothesis because the number of quadrivalents observed in 93 cells is significantly less than predicted by the Jackson‐Casey‐Hauber model for autotetraploids that have zero to two chiasma per pachytene bivalent. Enzyme electrophoresis was used to test the alternative hypothesis of allotetraploidy and to determine possible diploid progenitor(s). Eleven enzymes encoded by 25 loci were resolved for the three species in this complex. Marshallia mohrii exhibits fixed heterozygosity for the polymorphic loci. The diploid species possess three duplicated loci, one for isocitrate dehydrogenase and two for phosphoglucose isomerase. Of sixteen alleles among the polymorphic loci in M. mohrii, one allele (for Tpi‐1) is also found in M. trinervia, and three alleles (one each for Tpi‐1, Tpi‐2, and Lap) are found in M. grandiflora. Marshallia mohrii also possesses one allele each at Idh‐1, Idh‐2, Pgi‐4, and two each at Me and Mnr that are not shared with either of the two diploid species analyzed in this study. The cytogenetic and electrophoretic evidence suggest an allotetraploid origin of M. mohrii, possibly involving M. grandiflora, M. trinervia, and a third species. Inferences about ancestry are difficult because of the paucity of qualitative allozyme divergence among the diploids and because of the number of high frequency alleles in M. mohrii, not found in either M. grandiflora or M. trinervia.
MESOCOTYL ROOT FORMATION IN ECHINOCHLOA PHYLLOPOGON (POACEAE) IN RELATION TO ROOT ZONE AERATION
Authors: Everard John D. , LeCain Daniel R. , Rumpho Mary E. , Kennedy Robert A.
Published: January 2018

Echinochloa phyllopogon was grown hydroponically under four root zone gassing treatments to determine aeration effects on the growth and development of the plant root system. Although mesocotyl growth and the number of nodal roots were unaffected by the treatments, other aspects of plant growth were altered. Shoot growth was reduced by hypoxic (5 kPa partial pressure O2 in nitrogen gas) and anoxic conditions (O2 free nitrogen gas), but not by ethylene (0.1 ppm in air). Seminal root growth was unaffected by hypoxia or ethylene treatments, but was reduced under anoxia. Hypoxic environments stimulated the emergence of roots along the length of the mesocotyl when compared to aerobic controls; anoxic and ethylene treatments had no significant effects. Mesocotyl roots elongated from primordia that were produced de novo in response to the hypoxic treatment. Under hypoxic conditions, aerenchyma was present in the cortex of nodal roots and to a lesser extent in seminal roots, but mesocotyl roots were devoid of aerenchyma under these conditions. The results are compared with the literature concerning flooding and aeration effects on growth and development in other species.
GENETIC RELATIONSHIPS AND PATTERNS OF ALLOZYMIC DIVERGENCE IN THE IPOMOPSIS AGGREGATA COMPLEX AND RELATED SPECIES (POLEMONIACEAE)
Authors: Wolf Paul G. , Soltis Pamela S. , Soltis Douglas E.
Published: January 2018

The Ipomopsis aggregata complex consists of diploid, outcrossing, perennial herbs. The group is highly variable morphologically and is treated as three species: I. aggregata, I. tenuituba, and I. arizonica. Geographic races of I. aggregata and I. tenuituba are recognized as subspecies. Enzyme electrophoresis was used to examine genetic relationships among populations and taxa in the Ipomopsis aggregata complex and some related species. Genetic data for 23 allozyme loci from 60 populations were also used to determine how genetic variation is distributed geographically. Populations in the southwestern United States were more variable than those in the northwest: the center of genetic diversity corresponded to the center of species diversity. Allozymic data provided no evidence of loss of genetic variability associated with recent and rapid divergence. Genetic relationships based on Nei's genetic identity did not correspond to taxonomic relationships. For example, populations of both I. arizonica and I. tenuituba clustered within I. aggregata. Despite relatively high levels of genetic diversity among populations, diversity among taxa was low. Results indicated that floral divergence and concomitant speciation have occurred recently in the Ipomopsis aggregata complex. Allozymic patterns also reflected convergent evolution for floral morphology and possible introgression. Despite morphological differences among species, insufficient evolutionary time has elapsed for allelic fixation at neutral or near‐neutral allozyme loci.
VARIATION IN SEX EXPRESSION IN CANADA YEW (TAXUS CANADENSIS)
Authors: Allison Taber D.
Published: January 2018

Sex expression was measured in several Canada yew (Taxus canadensis Marsh.) populations of the Apostle Islands of Wisconsin and southeastern Minnesota to determine the extent of variation within and among populations. Sex expression was recorded qualitatively (monoecious, male, or female) and quantitatively (by male to female strobilus ratios or standardized phenotypic gender). No discernible trends in differences in sex expression among populations or habitats were recorded. Trends in sex expression of individuals within populations were complex. Small yews tended to be male or, if monoecious, had female‐biased strobilus ratios. Large yews were monoecious but had male‐biased strobilus ratios. Phenotypic gender, recorded as relative maleness, however, was negatively, but weakly, correlated with plant size. Gender distribution in four of five populations was bimodal, suggesting that cosexual populations consist of male and female morphs. Strobilus ratios of individuals in Apostle Island populations showed significant annual variation, but gender for these same plants was significantly correlated from year to year. Annual adjustments in gender were most pronounced in small yews. The results indicate that relative investment in male and female reproductive structures by Canada yew individuals is responsive to environmental variation, but sex expression also has a proximate genetic component.
COMPARATIVE RESTRICTION SITE MAPPING OF CHLOROPLAST DNA IMPLIES NEW PHYLOGENETIC RELATIONSHIPS WITHIN RUBIACEAE
Authors: Bremer Birgitta , Jansen Robert K.
Published: January 2018

Phylogenetic analyses of 33 species of Rubiaceae were performed using chloroplast DNA restriction site mutations. Complete cleavage maps of eight enzymes were constructed for Psychotria bacteriophila and used as a reference in comparisons among other species. The species examined represent 33 genera from 18 tribes and four subfamilies of the Rubiaceae. A total of 268 restriction site mutations was detected, 161 of which were phylogenetically informative. Wagner and Dollo parsimony trees were compared to the classifications of Verdcourt, Bremekamp, and Robbrecht. The Wagner analysis resulted in six equally parsimonious trees with 348 steps and 54% homoplasy. Dollo analysis resulted in a single most parsimonious tree. Most clades were identical in the two analyses. The subfamily Cinchonoideae is paraphyletic. The subfamilies Antirheoideae, Ixoroideae, and Rubioideae are monophyletic, although their circumscriptions differ from previous classifications. Several new phylogenetic relationships are indicated: the tribe Chiococceae (Ixoroideae) groups with Exostema and Coutarea (Cinchonoideae); the subfamily Ixoroideae including tribe Vanguerieae is closely related to Pogonopus, Pinckneya, Calycophyllum, and Mussaenda (Cinchonoideae); and tribe Hamelieae forms a monophyletic group outside the subfamily Rubioideae.
CYCLING OF STOMATAL APERTURE IN LEAVES OF PLANTS WITH CRASSULACEAN ACID METABOLISM UNDER CONSTANT CONDITIONS
Authors: Thimann Kenneth V. , Tan Zhi‐Yi , Park Jonathon
Published: January 2018

When leaves of plants with C3 metabolism are detached and held in darkness, they senesce and the stomata close. Because the relation of senescence and stomatal closure is very close, if not actually causal, the question arose as to whether in the leaves of plants with Crassulacean acid metabolism whose stomata open at night the relationship to senescence would be reversed. Detached leaves of four species of Hoya, floated on water in constant darkness or constant light, were found to show no large differences in stomatal aperture (measured as diffusion resistance) between those in the light or dark, but the aperture changed in a regular circadian rhythm. In some leaves the rhythm was simple, in others the peak showed small secondary peaks, but in all cases the values were nearly the same in the light as in the dark, throughout the cycle. Previous culture of the intact plants under normal day/night conditions gave results similar to those with plants that had had prolonged culture under constant light or darkness. In those cases when the stomata were more open in the dark, the chlorophyll content was greater than when the stomata were more open in the light; but when they were more open in the light, the chlorophyll content showed little difference between light and dark. When the leaves had only their petioles in water they showed greater senescence in the light than in the dark, and the stomata were more tightly closed in the light, especially at the apical ends. All four species of Hoya gave similar results. We deduce that senescence of these leaves is modified by stomatal aperture, and generally in the same direction as in C3 leaves, but that in continuous light or darkness the primary control over the aperture is the endogenous cycle.
THE DEVELOPMENT OF THE FEMALE GAMETOPHYTE OF EPIPACTIS (ORCHIDACEAE) AND ITS INFERENCE FOR REPRODUCTIVE ECOLOGY
Authors: Fredrikson Margit
Published: January 2018

The development of the female gametophytes ofEpipactis atrorubens, E. helleborine,andE. palustrishave been investigated using confocal scanning laser microscopy. These species have T‐tetrads and eight‐nucleate female gametophytes in common. The development of the female gametophyte is monosporic in accordance with thePolygonumtype. Furthermore, the outer integument grows slowly and reaches to the middle of the inner integument, when the female gametophyte is mature. In the first two species, T‐tetrads develop prior to anthesis, which may be correlated with autogamy. The development of the female gametophyte ofE. palustrisappears to be similar in plants from different localities.
PATTERNS OF HYBRIDIZATION AND INTROGRESSION IN POPULATIONS OF OAKS, MANZANITAS, AND IRISES
Authors: Nason John D. , Ellstrand Norman C. , Arnold Michael L.
Published: January 2018

We used a maximum likelihood (ML) method to examine hybridization and introgression in mixed populations of black oaks (Quercus kelloggii and Q. wislizenii var. frutescens), manzanitas (Arctostaphylos patula and A. viscida), and irises (Iris fulva and I. hexagona). This method uses codominant molecular markers, such as allozymes and restriction fragment length polymorphisms, to estimate the frequencies of six genealogical classes of individuals (parental species, F1 and F2 hybrids, and first generation backcrosses) present in a mixed population. We contrasted these estimates with those from the traditional “direct method” which estimates hybrid frequencies directly from observed frequencies of molecular phenotypes. Both methods indicated that the putative hybrid oaks were all F1 hybrids. For the manzanitas, only ML estimates could reject the hypothesis that introgression was limited to first generation backcrossing. At least 27% of the individuals were estimated to represent second or later generation introgressants. Analysis of the irises indicated bidirectional localized introgression. These methods, in conjunction with clinal variation in the frequency of marker alleles, indicated that this pattern of introgression probably resulted from asymmetric density‐dependent gene flow by pollen. The ML method provides a more reliable description of the pattern of hybridization and introgression because it accounts for overlap among parental species and hybrid phenotype distributions.
LEAF INITIATION CORRELATES WITH TIME OF MAXIMAL SENSITIVITY OF THE SDP XANTHIUM (ASTERACEAE) TO DARK INTERRUPTION
Authors: Jacobs William P.
Published: January 2018

The hypothesis was tested that the well‐known maximal sensitivity to a light break at or near the middle of the dark period of short‐day plant Xanthium is correlated with a specific stage of leaf initiation. Samples were collected at various hours before and during noninductive 6‐hr dark periods. Lengths of leaf primordia were calculated from serial transverse sections. The reproducible results confirmed that leaf initiation occurred at or near middark under the 18:6 hr light: dark growing conditions. The author suggests the working hypothesis that for a light break to be effective in nullifying the effect of a “long” night in photoperiodically sensitive plants, the light must react with a specific early stage of leaf initiation.
PATTERNS OF PROTEIN ACCUMULATION IN DEVELOPING ANTHERS OF LILIUM LONGIFLORUM CORRELATE WITH HISTOLOGICAL EVENTS
Authors: Wang Co‐Shine , Walling Linda L. , Eckard Kathleen J. , Lord Elizabeth M.
Published: January 2018

Differentiation in the anther of Lilium longiflorum occurs in discrete stages that correlate well with flower bud length. Using both sodium dodecyl sulfate and two‐dimensional polyacrylamide gel electrophoresis, detectable proteins that accumulated during the development of lily anthers were documented. In terms of histology and protein patterns, anther ontogeny was divided into three major phases. Phase I encompassed early proliferative stages as well as the differentiation of the locules. Phase II extended from the onset of meiosis through to mature microspores. Phase III began after microspore mitosis occurred to form pollen. Ten floral organ‐enriched and 17 floral organ‐specific polypeptides were detected during development. The appearance and disappearance of these polypeptides correlated well with the transitions between phases. Two groups of floral organ‐specific proteins in Phase II were chosen for further analysis. Both groups of polypeptides were stamen‐specific. The 15.0 kD proteins were anther‐specific and were the most abundant floral proteins detected; the 75.0 kD proteins were detected in both the anther and filament.
SECRETORY VESICLE FORMATION IN GLANDULAR TRICHOMES OF CANNABIS SATIVA (CANNABACEAE)
Authors: Mahlberg Paul G. , Kim Eun‐Soo
Published: January 2018

Formation of secretory vesicles in the noncellular secretory cavity of glandular trichomes of Cannabis saliva L. was examined by transmission electron microscopy. Two patterns of vesicle formation occurred during gland morphogenesis. 1) During initial phases of cavity formation small hyaline areas arose in the wall near the plasma membrane of the disc cell. Hyaline areas of elongated shape and different sizes were distributed throughout the wall and adjacent to the secretory cavity. Hyaline areas increased in size, some possibly fusing with others. These hyaline areas, possessing a membrane, moved into the cavity where they formed vesicles. As membraned vesicles they developed a more or less round shape and their contents became electron‐dense. 2) During development of the secretory cavity and when abundant secretions were present in the disc cells, these secretions passed through the wall to accumulate as membraned vesicles of different sizes in the cavity. As secretions emerged from the wall, a membrane of wall origin delimited the secretory material from cavity contents. Vesicles released from the wall migrated in the secretory cavity and contacted the sheath where their contents permeated into the subcuticular wall as large or diffused quantities of secretions. In the subcuticular wall these secretions migrated to the wall–cuticle interface where they contributed to structural thickening of the cuticle. This study demonstrates that the secretory process in glands of Cannabis involves not only secretion of materials from the disc cell, but that the disc cell somehow packages these secretions into membraned vesicles outside the cell wall prior to deposition into the secretory cavity for subsequent structural development of the sheath.
ORIGIN AND ONTOGENESIS OF SOMATIC EMBRYOS IN HEYEA BRASILIENSIS (EUPHORBIACEAE)
Authors: Michaux‐Ferrière N. , Grout H. , Carron M. P.
Published: January 2018

In Hevea, currently described culture conditions allow the induction of two modes of embryogenesis in callus formed on excised portions of the internal integument of immature seeds. One mode is of unicellular origin and is transitory, only resulting in the production of globular proembryos. The other is of multicellular origin and produces embryos. Specific culture conditions appear to favor one or the other mode of development in a given genotype. The ontogenesis of embryos of multicellular origin bypasses the classical stages of zygotic embryogenesis. The structural abnormalities observed in most somatic embryos are probably responsible for the low germination rates obtained.
FRUITS AND SEEDS OF TRIBE GORDONIEAE (THEACEAE) FROM THE EOCENE OF NORTH AMERICA
Authors: Grote Paul J. , Dilcher David L.
Published: January 2018

A new genus and species Gordoniopsis polysperma and two new species of Gordonia (Gordonieae, Camellioideae, Theaceae) are described based on fossil fruit and seed remains. These specimens are part of a large flora consisting of various plant organs from the middle Eocene Claiborne Formation in western Kentucky and Tennessee. Gordoniopsis is a five‐valved loculicidally dehiscent capsule similar to capsules of Gordonia but differing in having unwinged seeds and a greater number of seeds per locule. The two Gordonia species are among the earliest unequivocal records of the genus and two of only four fossil Gordonia species known with in situ seeds. Two extinct genera, Gordoniopsis and Andrewsiocarpon, and the extant genus Gordonia in the tribe Gordonieae are known from the middle Eocene Claiborne flora, suggesting an early radiation within the tribe. Based on a survey of Recent fruits and seeds we concur with Keng's proposal to merge Laplacea with Gordonia.
THE GENETICS OF GENDER AND THE EFFECTS OF GENDER ON FLORAL CHARACTERS IN GYNODIOECIOUS PHACELIA LINEARIS (HYDROPHYLLACEAE)
Authors: Eckhart Vincent M.
Published: January 2018

The evolution of gynodioecy depends in part on the location (nucleus or cytoplasm) of gender‐determining genes. Characters genetically correlated with gender also can be important in the evolution of this sexual system. For example, gender differences in the costs of flowers affect the potential for resource compensation by females for the loss of male function. This paper reports the genetics of gender and the nature of secondary sex characters of flowers in Phacelia linearis (Hydrophyllaceae), a gynodioecious annual in which females exhibit substantial compensation. A single nuclear gene has a major effect on gender, recessive homozygotes being male‐sterile, but not all the data can be explained by this or other simple inheritance models. In nature, hermaphrodites have wider corollas than females and begin to flower slightly later than females. In a common environment, gender effects on corolla size are modified by genetic background and/or maternal effects. Hermaphrodite flowers have 15% greater dry biomass than female flowers, but similar ovule number and nectar sugar production. Hermaphrodite and female flowers differ in the linear dimensions and biomass allocation of several floral organs. In particular, the androecia and corollas of female flowers are smaller than those of hermaphrodite flowers, both in absolute terms and relative to the size of the rest of the flower. Corolla size reduction could be an important source of resources for compensation by females.
PHYSIOLOGICAL SENSITIVITY OF PLANTS ALONG AN ELEVATIONAL GRADIENT TO UV‐B RADIATION
Authors: Ziska L. H. , Teramura A. H. , Sullivan J. H.
Published: January 2018

Seeds from four plant pairs collected from contrasting elevations in Hawaii were grown in greenhouses at the University of Maryland at UV‐B radiation levels that approximated a 20% and 40% stratospheric ozone depletion anticipated at sea level in Maui. In general, increases in UV‐B radiation resulted in earlier reproductive effort, increased dark respiration and maintenance of relative water content (RWC), photosynthesis, and apparent quantum efficiency (AQE) in plants from higher elevations where natural UV‐B radiation is already high. In contrast, plants collected from low elevational ranges showed a significant decline in average plant and floral dry biomass, a decline in AQE and RWC, and a reduction in light‐saturated photosynthetic capacity. Increases in UV‐B‐absorbing compounds (e.g., flavonoids), were noted for low elevation but not high elevation plants. However, plants from high elevations produced a consistently larger amount of these compounds even in the absence of UV‐B radiation. This study suggests that plants growing in a naturally high UV‐B environment may have developed or maintained mechanisms related to reproductive phenology and carbon uptake which may maintain productivity in a high UV‐B environment. This would also suggest that ecotypic differentiation may have occurred in response to increasing UV‐B radiation over an elevational gradient. The range of adaptability to increased UV‐B also implies changes in species and community dynamics that might be anticipated in natural plant populations if stratospheric ozone depletion continues.
TAXONOMIC AND GEOGRAPHIC DISTRIBUTION OF INTERNAL GEITONOGAMY IN NEW WORLD CALLITRICHE (CALLITRICHACEAE)
Authors: Philbrick C. Thomas , Bernardello Luis M.
Published: January 2018

Internal geitonogamy (IG) is a unique self‐fertilization system that occurs in the genus Callitriche. In IG self‐fertilization is effected by pollen tube growth through vegetative tissues from the staminate to pistillate flowers. IG occurs in seven of the 22 species of Callitriche in the New World (C. heterophylla, C. heteropoda, C. lechleri, C. nubigena, C. rimosa, C. trochlearis, C. verna). Callitriche verna occurs in both the New and Old Worlds and represents the only known instance of IG in the latter region. IG is correlated with the amphibious growth habit and polyploidy, although not all polyploid amphibious species of Callitriche have IG. Correlations between IG and geographic distribution are not apparent. There is a tendency for species that possess IG to occur at higher elevations than those that lack this system.
POLLEN AND OVULE SOURCES AFFECT SEED PRODUCTION OF LOBELIA CARDINALIS (LOBELIACE AE)
Authors: Schlichting Carl D. , Devlin B.
Published: January 2018

To examine the breeding system and components of male and female reproductive success in the hermaphroditic plant Lobelia cardinalis, we performed three crossing experiments with plants taken from natural populations. The experiments were designed to determine if the crossing success of plants as pollen and ovule parents was affected by the distance among mates, including self‐pollinations and pollinations between populations; to determine if plants differed in their abilities to sire or mature seed; and to determine if there was a correlation between a plant's success at siring and maturing seed. Selfpollinations resulted in significantly fewer seeds per fruit and significantly smaller seeds. There were no significant differences in germinability between selfed and outcrossed seeds. Distance among parents within a population did not affect any of the traits. Outcrosses within and between population produced similar numbers of seeds per fruit, similar seed weights, and similar germination success. There were highly significant differences among maternal plants in all three experiments in the number of seeds they matured, mean seed weight, and seed germinability. The maternal parent was the most important factor determining seed production, but there were also significant differences among paternal plants in the number of seeds they sired (all three experiments), in the germinability of the seeds they sired (two experiments), and in the sizes of seeds they sired (one experiment). Our results indicate that differences in success of Lobelia plants as male parents cannot be due solely to their relatedness to the female parent.
A NEW SPECIES OF MARSILEA FROM THE DAKOTA FORMATION IN CENTRAL KANSAS
Authors: Skog Judith E. , Dilcher David L.
Published: January 2018

Discovery of compression/impression megafossil material from the Cenomanian (mid‐Cretaceous) in Kansas documents the occurrence of the genus Marsilea during this age. Only vegetative material has been found as complete plants; associated structures that may be fertile structures could belong to the genus also. This new fossil species extends the megafossil record of the genus back to the mid‐Cretaceous when previously only megaspores attributed to the family occurred during this time. The fossil record of the heterosporous aquatic fern families is reviewed with emphasis on the Marsileaceae.
A NEW SCIADOPITYACEOUS SEED CONE FROM THE UPPER CRETACEOUS OF HOKKAIDO, JAPAN
Authors: Saiki Ken'ichi
Published: January 2018

A sciadopityaceous seed cone, Sciadopityostrobus kerae, gen. et sp. nov., is described on the basis of a permineralized specimen from the Upper Cretaceous (Cenomanian–Coniacian) of Hokkaido, Japan. The peel method was applied for anatomical observations. The seed cone consists of a cone axis receiving numerous cone scale complexes that are arranged helically. Each complex generally has five inverted ovules that are oriented adaxially. The cone is similar to those of living Sciadopitys verticillata with respect to its peltate cone scale complex, with free apices of both bract and ovuliferous scale, trichomes on the bract, and a trifurcated ovuliferous scale strand. In the fossil, the bract and ovuliferous scale strands fuse with each other in the basal part of the cone scale complex, while S. verticillata bract and ovuliferous scale strands are derived separately from the vascular cylinder and remain separate throughout their length. The present specimen is one of the oldest records of structurally preserved cones that can be assigned to the family Sciadopityaceae.
MEASURING THE HYDRAULIC DIAMETER OF A PORE OR CONDUIT
Authors: Lewis Ann M.
Published: January 2018

A method for estimating the hydraulic diameter of a pore or conduit having a noncircular opening is presented with special reference to plant anatomy. An ellipse or a rectangle is inscribed within the opening, and the length of the short axis (a) is measured. The hydraulic diameter (Dh) is estimated for the ellipse (Dh = 1.4a) or rectangle (Dh = 2a). Use of these equations often gives a more accurate estimate of the hydraulic diameter of a pore or conduit than does averaging the lengths of the short and long axes (Dh = [a + b]/2, b is the long axis) or assuming that the opening is circular (Dh = a). A table of the error in each method is included, and the errors inherent in the use of Dh are discussed. Because fewer measurements are required, estimation based on the measurement of one axis is much faster than calculation using both the short and long axes. The equations and table should permit anatomists and physiologists to rapidly determine the best method for estimating the hydraulic diameter of a pore or conduit, and to more accurately and quickly estimate the hydraulic diameters of large numbers of openings. However, because of potential pitfalls in applying theoretical fluid dynamics equations to real‐world functional anatomy, botanists must ensure that their applications of hydraulic diameter are appropriate in each case.
PLANTING DENSITY INFLUENCES THE EXPRESSION OF GENETIC VARIATION IN SEED MASS IN WILD RADISH (RAPHANUS SATIVUS L.: BRASSICACEAE)
Authors: Mazer Susan J. , Wolfe Lorne M.
Published: January 2018

To determine the effects of density, genotype, and their interaction on individual seed mass in Raphanus sativus L., we replicated maternal and paternal families of seed across two planting densities in an experimental garden. Seeds were produced by a nested breeding design performed in the greenhouse. Among garden‐raised plants, density had a strong negative effect on the mass of seeds produced. At low density, the identity of the greenhouse‐grown maternal plants had a strong effect on F2 seed mass, while in high‐density plots, there were no significant parental effects on mean seed mass. Significant parental genotype density interactions contributed to variation in F2 seed mass. Norms of reaction for each of the 15 paternal sibships illustrate paternal family density interactions. Three sibships exhibited significant declines in mean seed mass with increasing density; 12 sibships showed no change. Maternal family density interaction effects on seed mass were also detected; among maternal sibships, mean seed mass at low density was negatively correlated with mean seed mass at high density. These results demonstrate: a) planting density has a strong effect on mean individual seed mass produced by adults; b) density influences the magnitude of maternal effects on progeny phenotype; and c) genotype density interactions influence seed mass, potentially contributing to the maintenance of maternal genetic variation in seed mass in natural populations of wild radish.
INTERNAL PHLOEM IN THE PULVINUS OF SOYBEAN PLANTS
Authors: Grignon Nicole , Touraine Bruno , Grignon Claude
Published: January 2018

Glycine max, like many species of Fabaceae, has pulvini at the base of the petiole. In this structure, the vascular cylinder is constricted and consists of a ring of phloem surrounding a ring of xylem. A combination of light and transmission electron microscopy and histochemistry showed that, in addition, there are groups of internal phloem strands in the pulvinar pith. This was confirmed by direct observation of sieve plates and crystalline P‐protein inclusions typical of leguminous sievetube members. Serial sections through the stem–pulvinus–petiole revealed that a spatial reorientation of the vascular tissue in the pulvinus resulted in the formation of internal phloem strands, which are continuous with the external phloem bundles above and below the pulvinus. Using 6(5)carboxyfluorescein (6CF) as a fluorescent tracer of phloem transport, we have shown that the internal phloem was active. In most of the experiments, when 6CF was applied to a source leaf, the internal phloem was not stained when the stem was girdled between the source leaf and the roots. Thus, we suggest that the internal phloem of the pulvinus of soybean is specialized for transport toward the root.
INFLUENCE OF FLOWER CHARACTERISTICS, WEATHER, TIME OF DAY, AND SEASON ON INSECT VISITATION RATES IN THREE PLANT COMMUNITIES
Authors: McCall Claire , Primack Richard B.
Published: January 2018

Pollination biology at the community level was investigated using quantitative techniques, comparative methodology, measurements of the physical habitat, and consideration of floral characteristics. The frequency of insect visits to flowers was investigated in three contrasting communities: a deciduous woodland‐meadow site in eastern Massachusetts, alpine tundra in New Hampshire, and Mediterranean scrub (fynbos) in South Africa. Visits to flowers were most common in woodland‐meadow, followed by alpine tundra, and least frequent in fynbos. Bees were the most common visitor in the woodland‐meadow and the fynbos, but flies were the most common visitor in the tundra. Flower color often influenced visitation rates and had a weak but significant effect on the type of insect that visited flowers. Preferences for color by different types of insects often changed in different communities, which suggests that floral syndromes may be community‐specific. In all communities, tubular flowers were visited less often than open flowers. Less specialized insects were more common on open than tubular flowers, but large variances made few differences statistically significant. Combining measurements of temperature, light, humidity, wind speed, time of day, and season (using cluster analysis) with the shape of a flower, it was predicted that a 10‐minute observation would include at least one visit. Flower shape, temperature, light, and season appear to be the most important variables influencing insect visitation rates. Results of this study indicate that relationships between insects and flowers are nonspecific and vary among communities.