bluuebunny/crossref_metadata_2025 huggingface dataset:
INHERITANCE OF NUCLEAR 2C DNA CONTENT VARIATION IN INTRASPECIFIC AND INTERSPECIFIC HYBRIDS OF MICROSERIS (ASTERACEAE)
Authors: Price H. James , Chambers Kenton L. , Bachmann Konrad , Riggs Jennifer
Published: January 2018

Nuclear DNA content varies over 20% within the diploid (2n = 18) species M. douglasii and M. bigelovii. Two different intraspecific crosses were made between M. douglasii biotypes which differed by about 10% in 2C nuclear DNA content. The F2 progeny of one intraspecific cross showed no striking evidence of segregation for DNA content. The mean DNA contents of F2 progeny from two sister hybrids from the second intraspecific cross were significantly different at the 1% level.

An interspecific cross was made between biotypes of M. douglasii and M. bigelovii that differed by approximately 10% in DNA amount. The 12 F1 progeny did not cluster around the parental midpoint, but instead encompassed nearly the entire range between the parental means. The five families of F2 progeny studied each had a mean DNA content corresponding to that of the particular F1 from which they were derived, indicating that the F1 plants were not of identical DNA content.

The results of this study suggest that DNA sequences which account for the DNA content differences among the plants are unstable and can undergo deletion or amplification in a hybrid. The altered DNA content may be heritably stable and show little or no segregation in the F2 progeny.
THE RELATIONSHIP BETWEEN THE PRIMARY THICKENING MERISTEM AND THE SECONDARY THICKENING MERISTEM IN YUCCA WHIPPLEI TORR. I. HISTOLOGY OF THE MATURE VEGETATIVE STEM
Authors: Diggle Pamela K. , DeMason Darleen A.
Published: January 2018

Anatomical observations were made on 1‐, 2‐, and 3‐yr‐old plants of Yucca whipplei Torr, ssp. percursa Haines grown from seed collected from a single parent in Refugio Canyon, Santa Barbara, California. The primary body of the vegetative stem consists of cortex and central cylinder with a central pith. Parenchyma cells in the ground tissue are arranged in anticlinal cell files continuous from beneath the leaf bases, through the cortex and central cylinder to the pith. Individual vascular bundles in the primary body have a collateral arrangement of xylem and phloem. The parenchyma cells of the ground tissue of the secondary body are also arranged in files continuous with those of the primary parenchyma. Secondary vascular bundles have an amphivasal arrangement and an undulating path with frequent anastomoses. Primary and secondary vascular bundles are longitudinally continuous. The primary thickening meristem (PTM) is longitudinally continuous with the secondary thickening meristem (STM). Axillary buds initiated during primary growth were observed in the leaf axils. The STM becomes more active prior to and during root initiation. Layers of secondary vascular bundles are associated with root formation.
DYNAMICS OF SYNTHETIC PHLOX DRUMMONDII POPULATIONS AT THE SPECIES MARGIN
Authors: Levin Donald A. , Clay Keith
Published: January 2018

We compare the dynamics of artificial populations of the annual Phlox drummondii introduced along a transect extending from within to beyond the species margin southwest of San Antonio, Texas. The margin is defined by a shift from sandy, nutrient poor soils to clay, nutrient‐rich soils. Fourteen sites were chosen along the 6.5‐mi transect. In each site seeds were planted into 1.5‐m‐square cleared plots and uncleared 10‐m transects. Transplants also were introduced into cleared plots. Survival, flower production and seed set were monitored over the course of the growing season. Individual fitnesses and the reproductive rates of artificial populations generally declined as the distance from the margin increased. The results indicate soil type per se is not limiting Phlox and that plants can successfully grow and reproduce, albeit at a reduced level, in sites beyond their natural margin.
PHLOEM STRUCTURE IN THE CARBONIFEROUS FERN PSARONIUS (MARATTIALES)
Authors: Smoot Edith L.
Published: January 2018

Phloem anatomy in stems ofPsaroniusis described from coal ball specimens collected at the Berryville, IL and Lewis Creek, KY localities. Phloem completely surrounds the C‐shaped xylem segments, but is more extensively developed on the abaxial side of the trace. The phloem zone consists of a central band of large diameter (approximately 90–120 μm) sieve elements surrounded by a mixed zone of smaller sieve elements and phloem parenchyma. Phloem is separated from the xylem by a parenchymatous xylem sheath. On the abaxial side of the trace, a discontinuous arc of very small diameter cells (7.8 μm) is present between the xylem sheath and the metaxylem. These cells corrrespond in position and size to protophloem cells in living marattialeans. Metaphloem sieve elements exhibit discrete, circular‐oval sieve areas on their side and end walls, some of which show evidence of sieve pores. Phloem structure inPsaroniusis compared with that known for living members of the Marattiales.
THE ROLE OF RESIN IN ANGIOSPERM POLLINATION: ECOLOGICAL AND CHEMICAL CONSIDERATIONS
Authors: Armbruster W. Scott
Published: January 2018

Members of at least two unrelated genera of plants, Dalechampia (Euphorbiaceae) and Clusia (Guttiferae), attract pollinators by secreting resins from floral structures. Bees that pollinate these flowers collect and use the resin in nest construction; these include Euglossa, Eulaema, Eufriesea, Trígona and, Hypanthidium in the neotropics, and Heriades in Africa. Floral resins are slow in hardening as compared with many other plant resins; this facilitates collection and storage by bees, hence probably enhancing the attractiveness of the flowers. Floral resins are probably of great utility and dependability and may be an especially important resource to certain bees, which in turn are major pollinators of many species of tropical plants. Bees appear to forage floral resin using a “strategy” of energy efficiency; large bees collect resin only from copious sources, smaller bees collect resin from sources with small amounts as well as from sources with large amounts of resin. Resin secretion in flowers may have originated as defense against herbivores and secondarily assumed the role of pollinator reward.
SEED MORTALITY IN DAUCUS CAROTA POPULATIONS: LATITUDINAL EFFECTS
Authors: Lacey Elizabeth P.
Published: January 2018

Daucus carota, a common herbaceous weed, grows over a wide latitudinal range in eastern North America. Viability and germination tests of mature seeds collected from 36° to 45°N were conducted to measure predispersal seed mortality. Viability and germination declined as latitude of the seed source decreased. Only 30–50% of the seeds from southern populations germinated owing to high embryo inviability and absence of embryos. Sixty to ninety percent of the seeds from northern populations germinated. Reciprocal planting of seeds in outdoor experimental plots at three latitudes and testing of seeds over two generations together showed that the environment in which seeds mature, rather than environmental preconditioning over generations or genetically‐based differences among populations, explain this variation in germination ability. Within‐latitude germination declined in experimental plots as population age of the seed source within latitudes increased. The data indicate that predispersal seed mortality can influence local population persistence and that seed mortality is an increasingly important factor in population regulation at the southern limit of the species’ range.
ORDINATION AND CLASSIFICATION OF WESTERN OAK FORESTS IN OKLAHOMA
Authors: Dooley Karen L. , Collins Scott L.
Published: January 2018

Ordination and classification techniques were used to analyze patterns of forest vegetation, species diversity, and soil type in the Wichita Mountains Wildlife Refuge of southwestern Oklahoma. Cluster analysis based on tree species produced three general community types: 1) Quercus stellata‐Q. marilandica forests; 2) Q. stellata forests; and 3) mesophytic forests. A polar ordination produced a gradient of vegetation that corresponded to a moisture gradient. Many high diversity forests were located on loamy drainageway soils or north facing slopes. Tree species diversity (H') was inversely related to the importance of Quercus stellata. Cluster analysis based on species composition of the tree seedlings produced four general community types: 1) Q. marilandica type; 2) Q. marilandica‐Q. stellata‐Juniperus virginiana type; 3) Ulmus americana‐Celtis reticulata‐Bumelia lanuginosa type; and 4) Acer saccharum type. The third seedling type occurred almost exclusively on loamy drainageway soils. There was no relationship between stand location on the first axis of the tree ordination and the first axis of the seedling ordination suggesting that trees and seedlings respond differently along the moisture gradient.
EXPERIMENTAL NON‐STIGMATIC POLLINATIONS IN CLARKIA UNGUICULATA LINDL. (ONAGRACEAE)
Authors: Bowman Robert N.
Published: January 2018

Within angiosperms, the stigma‐style apparatus provides a barrier to direct contact between ovules and the external environment. In traversing this barrier, male gametophytes presumably are subject to intense competition and natural selection. Successful fertilizations and resultant seed set can be accomplished following surgical decapitation of the stigma and style, provided that these normally receptive sites are replaced with an optimal environment suitable for pollen germination and growth. Unlike other methodologies, these in situ‐in vitro pollinations are comparatively easily accomplished, and provide a means for circumventing natural fertility barriers; additionally, they may provide a simple means of artificially selecting pollen genomes. In Clarkia unguiculata 23.0% of attempted non‐stigmatic pollinations produced outcrossed F1 progeny.
ESTABLISHMENT OF A PLASTOCHRON INDEX FOR DIANTHUS CHINENSIS L.
Authors: McCauley Michele , Croxdale Judith
Published: January 2018

The plastochron index was used to determine which leaves of Dianthus chinensis are developmentally equivalent during vegetative growth of the shoot. Three conditions of the plastochron index had to be met in order for leaves to be defined as developmentally equivalent. The leaves had to be growing exponentially in their early stages, growing at the same rate, and initiated at equal intervals. Linear regression analysis was used to determine the goodness of fit of the exponential model and to calculate the relative rate of leaf elongation. Linear regression was also used to determine the relationship of leaf initiation to time. Both greenhouse‐grown (100 plants) and growth‐chamber‐grown (25 plants) D. chinensis were studied. Regression analysis of the greenhouse plants was performed only with values of averaged leaves. It was found that the greenhouse‐grown average leaves grow exponentially and are initiated at equal intervals, the plastochron equaling 4.55 days. The relative rates of leaf elongation are not constant, ranging from 0.05 to 0.16 cm cm−‐1 day−‐1. However, these rates are most likely the result of analyzing values of averaged leaves. Regression analysis of the growth‐chamber plants was performed with both average and individual leaves. The latter procedure provided a more accurate description of the data. It showed that the leaves of the growth‐chamber plants grow exponentially in their early stage, have the same relative rate of leaf elongation from Leaf 5 to Leaf 12 (0.23 ± 0.005 cm cm−‐1 day−‐1), and are initiated at equal intervals for Plastochrons 6–11 (3.68 ± 0.14 days). Therefore Leaves 6–12 of the growth‐chamber‐grown Dianthus chinensis meet the three criteria of the plastochron index and can be defined as developmentally equivalent from inception to maturation.
CYANOGENIC GLYCOSIDES OF CARICA PAPAYA AND ITS PHYLOGENETIC POSITION WITH RESPECT TO THE VIOLALES AND CAPPARALES
Authors: Spencer Kevin C. , Seigler David S.
Published: January 2018

Carica papaya L. (Caricaceae) was found to contain the cyclopentene‐ring containing cyanogenic glucoside tetraphyllin B as well as the aromatic cyanogenic glucoside prunasin. This is the first report of the isolation of cyanogenic glucosides from a species known to produce glucosinolates. The presence of both classes of compounds suggests that Carica papaya may be intermediate between the Capparales and the Violales.
THE MEGAGAMETOPHYTE OF HYDRASPERMA TENUIS LONG FROM THE UPPER DEVONIAN OF IRELAND
Authors: Matten Lawrence C. , Fine Tracey I. , Tanner William R. , Lacey William S.
Published: January 2018

Hydrasperma tenuis ovules containing cellular megagametophytes have been recovered from Upper Devonian (stage) strata near Ballyheigue, County Kerry, Ireland. The megagametophytes are elliptical in transverse section and obovate in longitudinal section. The vegetative cells are organized into three, distinct, concentric zones and exhibit the radial orientation characteristic of centripetal development. Up to three archegonia may be present at the apical end of the megagametophyte. They are elliptic to terete in cross‐section and elliptic in longitudinal section. Archegonia are thought to be sunken with each possessing a canal‐like connection to the surface of the megagametophyte. Archegonial jacket cells surround the egg cavity. A low, broad tent‐pole occurs at the top of the megagametophyte. This report represents the oldest, structurally‐preserved gymnosperm megagametophyte.
DEVELOPMENTAL ANATOMY AND HISTOCHEMISTRY OF LIGHT‐INDUCED CALLUS FORMATION BY DIÖON EDULE (ZAMIACEAE) SEEDLING ROOTS IN VITRO
Authors: Webb David T.
Published: January 2018

Light exposure caused massive areas of callus to develop from primary roots of aseptically cultured Diöon edule seedlings. Callus initiation and continued growth was due to cortical cell hypertrophy and subsequent periclinal cell division. Callus initiation occurred in the subdermal cortex and developed radially and centripetally from the locus of initiation. Callus formation encompassed virtually all of the cortex, but did not incorporate any of the vascular tissues. With very large calluses, sectors of internal periderm arose between the developing callus and the remaining quiescent cells of the inner cortex. Most of the callus cells were typical, vacuolate parenchyma with cellulose walls, and large, multilobed amyloplasts. Callus also contained idioblasts with globular deposits of polyphenols. Adjacent cortical cells were typical parenchyma with peripheral cytoplasm, but contained small plastids with little starch accumulation.
BASIDIOSPOROGENESIS IN BOLETUS RUBINELLUS. I. STERIGMAL INITIATION AND EARLY SPORE DEVELOPMENT
Authors: Yoon Kwon S. , McLaughlin David J.
Published: January 2018

Sterigmal initiation in Boletus rubinellus resembled hyphal tip growth. Four stages in early basidiospore development have been delineated based on gross morphology, and changes in wall layers and cytoplasm. Changes in wall layers and cytoplasm during spore development were stage‐specific. During Stage 1 the spore wall consisted of two layers identical to those of the sterigmal wall with occasional pellicle remnants on the outer surface. The onset of wall differentiation began in Stage 2, and during Stage 3 wall layers characteristic of the mature spore developed. At Stage 4 there was a pronounced gradient in wall thickness from the apex to the base of the spore. Small vesicles (30–60 nm diam) were uniformly distributed in the cytoplasm of spherically enlarging spores (Stage 2), but during spore elongation (Stages 3 and 4) numerous larger vesicles as well as small vesicles aggregated at the spore apex. A variety of cytoplasmic organelles entered the spore during Stage 3; however, migration of storage materials and the nucleus to the spore did not occur until late basidiospore development. The hilar appendix body developed in the earliest spore primordium and persisted until Stage 3. Development of wall layers and their differential thickening, distribution of vesicles, and probable function of the hilar appendix body are discussed with reference to the control of spore shape. Systematic implications of the data are considered.
ECOLOGICAL CONSTRAINTS ON WOOD DENSITY IN A TROPICAL MONTANE RAIN FOREST
Authors: Lawton Robert O.
Published: January 2018

In a Costa Rican tropical lower montane rain forest the wood densities of canopy tree species are related to the windiness of their preferred habitats, and to their abilities to tolerate shade. Shade‐intolerant species tend to have less dense wood than shade‐tolerant species from the same habitat. Species characteristic of windy sites tend to have denser wood than species characteristic of sheltered habitats. Stand mean wood density, the average of species’ wood densities weighted by their proportional contributions to stand basal area, increases with exposure to the wind. These trends in wood density should at least partially counteract the damaging effects of wind on exposed sites. Since investment in wood must come at the expense of growth elsewhere, such trends in wood density may help explain the small stature of elfin forest and montane thicket formations in tropical mountains.
ELEVATIONAL VARIATION IN FOLIAR FLAVONOIDS OF QUERCUS RUBRA L. (FAGACEAE)
Authors: McDougal Karen M. , Parks Clifford R.
Published: January 2018

Foliar extracts of high elevation Quercus rubra contain 20 major flavonol‐3‐0‐glycosides based primarily on the aglycones myricetin, quercetin, and kaempferol. These compounds display an altitudinal cline in the Appalachian mountains, with quercetin‐rich low elevation chemotypes intergrading into myricetin‐rich high elevation forms. These chemotypes appear to be correlated with previously documented variation in foliar morphology. The degree of interpopulation variation also differs with elevation. At higher elevations flavonoids differ only quantitatively between sites, while below 3,000 ft there is site‐to‐site variability in the hydroxylation level of the aglycones.
STERILITY BARRIERS OF SOME ARTIFICIAL F1 ORCHID HYBRIDS: MALE STERILITY. I. MICROSPOROGENESIS AND POLLEN GERMINATION
Authors: Stort Maria Neysa Silva
Published: January 2018

Microsporogenesis, pollen germination and fertility of males gametes were studied in 24 artificial intergeneric and interspecific F1 hybrids of orchids. Although parental species had the same chromosome number (2n = 40), microsporogenesis of the hybrids was irregular due to the lack of homology of the chromosomes of the parental species. This led to formation of tetrads of microspores without micronuclei, tetrads with 1–8 micronuclei, triads, dyads with and without micronuclei, and monads. Chromosomes numbers found in haploid microsporocytes ranged from 7 to 40; in micronuclei the chromosome number varied between 1 and 5.

In terms of pollen germination, three situations were observed: 1) hybrids whose pollen grains did not germinate in the stigma; 2) hybrids in which the pollen tubes grew down in the style, but did not penetrate into the ovary; 3) hybrids in which the pollen tubes grew down normally through the ovary, reaching the ovules. When the pollen tubes did not penetrate the ovary no fruit was formed. Therefore germination tests carried out in vitro may not indicate pollen fertility, because pollen tube growth in the style of the flower may be insufficient to induce fruit formation or to accomplish fertilization.
SPORE WALL DEVELOPMENT IN ANDREAEA (MUSCI: ANDREAEOPSIDA)
Authors: Brown Roy Curtiss , Lemmon Betty E.
Published: January 2018

The spore wall of Andreaea rothii (Andreaeopsida) is unique among mosses studied by transmission electron microscopy. The exine of other mosses is typically initiated on trilaminar structures of near unit membrane dimensions just outside the plasma membrane. The exine of Andreaea is initiated in the absence of such structures as discrete globules within the coarsely fibrillar network of the sporocyte wall. The sequence of wall layer development, nevertheless, is essentially like that of other mosses. The intine is deposited within the exine and the perine accumulates on the surface of the exine during the latter stages of spore maturation. The mature spore is weakly trilete and inaperturate. The wall consists of three layers, the inner intine, the spongy exine consisting of loosely compacted irregular globules of sporopollenin, and an outer layer of perine. The perine differs ultrastructurally from the exine only in its greater degree of electron opacity. This ultrastructural evidence of departure from the fundamental pattern of exine development in mosses supports the taxonomic isolation of Andreaea from mosses of the Sphagnopsida and Bryopsida.
DYNAMICS OF ARBUSCULE DEVELOPMENT AND DEGENERATION IN A ZEA MAYS MYCORRHIZA
Authors: Toth Ronald , Miller R. Michael
Published: January 2018

A quantitative light and electron microscope study of developing and degenerating mycorrhizal arbuscules of Glomus fasciculatum in Zea mays was carried out in order to estimate three parameters during the colonization cycle. These were: 1) Vv(f,c), the fraction of the host cell volume occupied by a volume of fungus; 2) Vv(cy,c), the fraction of the host cell volume occupied by host cytoplasm; 3) Sv(pr,c), the surface‐area‐to‐volume ratio of the host protoplast to the whole host cell. Uninfected cortical cells had an Sv(pr,c) of 0.13 μm2/μm3. As the fungus penetrates the cell wall, the protoplast invaginates, causing a decrease in protoplast volume and an increase in protoplast Sv. The Sv(pr,c) of a cell containing a mature arbuscule is 1.275 μm2/μm3. Because of the shrinkage of the protoplast, the Sv of the protoplast to its own volume rather than the original cell volume is 2.55 μm2/μm3, or almost a 20‐fold increase. Total cell size is unaffected. When the arbuscule is mature, the fungus occupies 42% of the cell, with 24% as 1‐μm‐diam branches, and 18% as trunk. Arbuscular branch formation progresses at a linear rate and is the most important factor in causing the increased host Sv. The correlation coefficient for Vv(br,c) the volume fraction for arbuscular branches, vs. Sv(pr,c) is r = 0.932 (P < 0.001). Degeneration of the arbuscule is marked by a rapid decrease in branches, host Sv, and host cytoplasm. The trunk develops and degenerates at a slower rate than the branches.
FLORAL NECTARIES AND TRICHOMES IN RELATION TO POLLINATION IN SOME SPECIES OF THEOBROMA AND HERRANIA (STERCULIACEAE)
Authors: Young Allen M. , Schaller Marilyn , Strand Melanie
Published: January 2018

Floral surfaces of two Theobroma spp. and one species of the allied genus Herrania (Sterculiaceae) were examined using scanning electron microscopy for reward system information of the pollinator‐adaptation syndrome. These flowers are structurally complex and have sheltered reproductive parts indicating an elaborate insect‐mediated pollination mechanism. Analysis of anther dehiscence, anthesis and pollen tube growth suggests a crepuscular pollination strategy. Suspected pollinators have been observed on floral parts of theobromas possessing stomate type nectaries and various shaped trichomes (blade of petal ligule and adaxial surface of petal hood). H. purpurea has elongate ligules devoid of stomates. Glandular clublike structures are found on the ovaries of all three spp. In numerous spp. of theobromas, except T. cacao, and two species of Herrania, a conspicuous ring of multicellular trichomes occurs at the adaxial base of the sepals. A possible function for the ring may be fragrance production because of its greatly reduced condition in the faintly scented T. cacao and the prevalence of pronounced fragrances in these other species.
AN ULTRASTRUCTURAL STUDY OF TRANSMITTING TISSUE DEVELOPMENT IN THE PISTIL OF LILIUM LEUCANTHUM
Authors: Gawlik Stanley R.
Published: January 2018

A study of developing transmitting tissue of Lilium Leucanthum pistils was undertaken in order to correlate structure with function. Lining the stylar canal are stigmatoid cells which contain a secretory zone consisting of a labyrinth of wall ingrowths characteristic of transfer cells. The functional feature of the labyrinth is a high surface‐to‐volume ratio that facilitates an intensive transmembrane flux of solutes. Stigmatoid cells in various stages of development and maturation have been investigated with the aid of electron and light optics in conjunction with cytochemical techniques. During development of the secretory zone, vesicles, formed by hypersecretory dictyosomes, fuse with the plasma membrane and contribute their contents to the growing wall. The pattern of secretory zone development is basipetal and is associated with initiation of chemotropism. In a mature pistil large crystals, having a basipetal pattern of development, and sensitive to protease, can be observed in the cytoplasm of stigmatoid cells. At anathesis, degradation of the crystal can be observed in the cells of the stigma surface and progresses basipetally as the pistil ages. The role of the crystal is uncertain. Immature pistils cultured in the presence of labeled proline take up the label which at maturity of the pistil is transferred to the canal of the pistil. The label is found in the crystals and the secretory zone of the stigmatoid cells. Pollen tubes growing in the canal of a labeled pistil take up the label.
COLEOCHAETE AND THE ORIGIN OF LAND PLANTS
Authors: Graham Linda E.
Published: January 2018

For a century the green algaColeochaetehas figured prominently in considerations of the origins of land plants (embryophytes). Certain of its advanced features contributed to Bower's (1908) theories on the origin of the land plant sporophyte by intercalation. Though Bower's ideas were disputed in later years, recent investigations ofColeochaeteand other green algae have lent strong support to them. At present it appears that further study ofColeochaeteand other charophycean algae may contribute much to our understanding of how a number of plant features, including reproductive ones, originated.
EXTRAFLORAL NECTARIES IN EBENACEAE: ANATOMY, MORPHOLOGY, AND DISTRIBUTION
Authors: Contreras Luz S. , Lersten Nels R.
Published: January 2018

Previous superficial reports, but only one anatomical study of one species, have supported the view that extrafloral nectaries (EFNs) of the unusual Benincasa type (i.e., with several layers of small nectariferous cells) of “Flachnektarien” (surface nectary) are common in Ebenaceae. An anatomical survey was made of 107 species (24% of the 450 species) of the four genera commonly accepted (Diospyros—73, Euclea—13, Maba— 12, Royena—9). There are 1–15 abaxial EFNs per leaf (two species each of Euclea and Royena had none). They were all of the Benincasa type, subtended by an irregularly 1–2‐layered sheath of cells with extremely thick radial walls. The pattern of minor vein association allowed recognition of two subtypes: apovascular (two or more subglandular layers between vein and sheath) and paravascular (one subglandular separating layer). Apovascular EFNs are smaller but more numerous per leaf, paravascular EFNs are larger but fewer per leaf. The apovascular subtype is most common in North America and Asia; a mixture of both subtypes occurs elsewhere; Euclea has only the latter subtype. Both subtypes have the most extensive vascular association yet described for Flachnektarien. They appear to have become specialized early in the family's evolution, before extensive migration occurred.
THE REPRODUCTIVE BIOLOGY OF RASPBERRIES AND PLANT‐POLLINATOR COMMUNITY STRUCTURE
Authors: Whitney Gordon G.
Published: January 2018

Rubus idaeus and Rubus pubescens are congeners which differ with respect to their life history patterns. Rubus idaeus is locally important in the Northeast in areas subject to windthrow, fire, and man‐made disturbances, while R. pubescens often forms a significant portion of the ground cover of shaded, damp, woodland areas. The life history pattern of R. idaeus is based upon the short term build up and slow decay of a large seed bank. Vegetative reproduction is more important in the eventual spread of R. pubescens. The reproductive traits of the two species reflect many of the above mentioned constraints and differences. Rubus pubescens produces relatively small quantities of nectar and flowers during a brief 1–2‐wk period late in May. Synchronous flowering probably minimizes the incidence of floral predation and makes the low nectar flowers more attractive by reducing the pollinators' flight time. Rubus idaeus is an abundant species, which offers almost unlimited supplies of nectar during at least part of its extended 3–4‐month flowering season. It is attractive to a wide range of pollinators and has figured prominently in the design, phenology, and reward structure of the early successional northern hardwoods plant‐pollinator community.
ARCHITECTURE AND CROWN GEOMETRY IN TABEBUIA ROSEA (BIGNONIACEAE)
Authors: Borchert R. , Tomlinson P. B.
Published: January 2018

In the tropical tree Tabebuia rosea, seedlings form an erect unbranched stem with rhythmic growth. Three distinct and predictable geometrical stages are then recognized in crown development. Sympodial branching begins with the arrest of the terminal bud of the trunk and symmetric outgrowth of a pair of subtending lateral buds. During an intermediate phase, branching becomes asymmetric at about Order 5. At each sympodial bifurcation there is differentiation between vigorous, relatively straight main branches (leaders) and less vigorous laterals forming regular pseudomonopodial branch complexes, which collectively constitute the cup‐shaped crown. Finally, dormant lateral buds in the lowest bifurcation of the trunk are released and reiterate the original crown form. Ultimately an erect, apparently monopodial tree is formed by a set of superimposed cup‐shaped crowns. Crown development of Tabebuia is unique because it involves predictable ontogenic changes in branching patterns. Crowns of open‐grown Tabebuia consist of relatively few, wide branch tiers, crowns of forest grown trees are tall and narrow. Analysis of the adaptive geometry of wide vs. narrow crowns through computer simulation illustrates the precise cost of mechanical support for terminal leaf rosettes at successive developmental phases and suggests that tall, erect, narrow, and multi‐tiered crowns are more efficient than wide open crowns.
REPRODUCTIVE FEATURES OF DENTARIA LACINIATA AND D. DIPHYLLA (CRUCIFERAE), AND THE IMPLICATIONS IN THE TAXONOMY OF THE EASTERN NORTH AMERICAN DENTARIA COMPLEX
Authors: Spooner David M.
Published: January 2018

Reproductive features including ovule development, megasporogenesis, megagametogenesis, microsporogenesis, microgametogenesis, pollen tube growth, embryogeny, and natural seed germination were studied in a single population each of Dentaria laciniata Muhl. ex. Willd. and D. diphylla Michx. to test for possible agamospermy. The population of D. laciniata studied is sexual. The archesporial cell functions directly as the megasporocyte. It undergoes two meiotic divisions, but the micropylar cell of the dyad fails to undergo meiosis II, and a linear triplet of three cells is formed. The chalazal megaspore divides to form an eight‐nucleate, seven‐celled megagametophyte of the Polygonum type. Simultaneous cytokinesis follows the second meiotic division of the microsporocyte yielding a tetrahedral tetrad of microspores. A three‐celled pollen grain is formed prior to anther dehiscence. Following apparent fertilization, the Capsella‐variation of the Onagrad type of embryogeny results in a conduplicate embryo. Endosperm is initially nuclear, but eventually becomes cellular. Seeds readily germinate in nature. Similar events are documented in one population of D. diphylla up to the organization of the embryo‐sac, which disintegrates before cellularization. These reproductive events and other data indicate that the eastern North American species of Dentaria may form a sexual polyploid complex with some sexual populations and some sterile ones.
FLOWER, FRUIT AND SEED ABORTION IN TROPICAL FOREST TREES: IMPLICATIONS FOR THE EVOLUTION OF PATERNAL AND MATERNAL REPRODUCTIVE PATTERNS
Authors: Bawa K. S. , Webb C. J.
Published: January 2018

Flower, fruit and immature seed abortion was studied in seven self‐incompatible species of trees in a tropical lowland semideciduous forest. The species showed considerable variability in fruit and seed set and the rate at which flowers and fruits were aborted. The amount of flower and fruit abortion also varied over time within species. Small samples of open‐pollinated flowers in three species showed adequate amounts of pollen on the stigma, but it could not be determined whether the pollen was compatible or incompatible. In a species with multiseeded fruits, the aborted fruits contained significantly fewer seeds than those retained on the plant. Position of fruit within the inflorescence and of seed within the ovary also had a marked effect on abortion: fruits and seeds at certain positions had a higher probability of abortion than those at other positions. Experiments to test the effect of pollen source on abortion were inconclusive. The factors underlying abortions were evaluated in the context of three mutually non‐exclusive hypotheses. It is concluded that selection for increased pollen dispersal and uncertainty in paternity of the zygotes are major factors underlying abortions.
WIND POLLINATION OF TAXUS CUSPIDATA
Authors: Niklas Karl J.
Published: January 2018

The air disturbance patterns created by and around the ovules of Taxus cuspidata are quantified for various orientations to the direction of ambient airflow, and are shown to largely dictate the motion (vectoral trajectories) and mode of deposition of windborne pollen on ovule surfaces. Perpendicular orientation to the direction of airflow results in two regions characterized by high densities of adhering pollen — one on the windward surface of the ovule, resulting from direct inertial collision, and another on the leeward surface resulting from non‐inertial sedimentation. Parallel and inclined orientations of the ovule to the direction of airflow produce quantitative and qualitative variations in the pattern of adhering pollen resulting from inertial and non‐inertial deposition. Direct collision of windborne pollen grains with the micropylar ends of ovules occurs for all orientations to wind direction. The aerodynamics of the ovulate shoot complex of Taxus cuspidata is related to that previously described for conifer ovulate cones, cycad megastrobili, and simulated wind tunnel analyses of archaic Paleozoic ovules based on scale models. Water transport of pollen (adhering to integument and bract surfaces) to micropyles quantitatively alters the distribution of adhering pollen grains on ovule surfaces. Although there is no evidence that pollen grains of this species are osmotically ruptured, observations do not preclude the possibility that water transport of pollen may reduce the number of viable pollen grains reaching the micropyle.
PHOTOSYNTHETIC RATE AND MESOPHYLL SURFACE AREA IN EXPANDING LEAVES OF ALTERNANTHERA PHILOXEROIDES GROWN AT TWO LIGHT LEVELS
Authors: Longstreth David J. , Bolaños Jorge A. , Goddard Russell H.
Published: January 2018

Leaves ofAlternanthera philoxeroides, alligator weed, developed at a photosynthetic photon flux density (PPFD, light energy at wavelengths of 400 to 700 nm) of 790 μmol sec−1m−2(High Light) had less surface area, were thicker, had a higher maximum Pn(net rate of CO2uptake), and required a higher PPFD for saturation of Pn, than leaves developed at 160 μmol sec−1m−2(Low Light). Mesophyll thickness at Low Light was within 19% of maximum 2 days after emergence but at High Light, thickness increased 79% between 2 and 16 days after leaf emergence. The ratio of mesophyll surface area to leaf surface area decreased during development in both light treatments; the ratio, however, was over 70% greater in fully expanded High Light leaves than in Low Light leaves. Maximum Pnexpressed on a leaf surface area basis was 158% greater in High Light leaves than in Low Light leaves, but Pnwas only 58% greater when expressed on a mesophyll surface area basis. It was estimated that fully expanded High Light leaves fixed 72% more CO2per leaf (Pnexpressed per unit surface area times the total surface area per leaf) than fully expanded Low Light leaves when Pnwas measured at the PPFD leaves expanded under. Both High and Low Light leaves would fix about the same amount of CO2per leaf when Pnwas measured at 160 μmol sec−1m−2because the larger surface area of the Low Light leaves offset small differences in Pn.
REPRODUCTIVE BIOLOGY OF TROPICAL LOWLAND RAIN FOREST TREES. I. SEXUAL SYSTEMS AND INCOMPATIBILITY MECHANISMS
Authors: Bawa K. S. , Perry D. R. , Beach J. H.
Published: January 2018

Sexual systems of tropical lowland rain forest trees were investigated to estimate the relative proportions of hermaphroditic, monoecious, and dioecious species. Controlled hand pollinations were performed on hermaphroditic species to determine the proportions of self‐compatible and self‐incompatible species. A total of 333 species was examined; 65.5% species were found to be hermaphroditic, 11.4% monoecious, and 23.1% dioecious. There were no differences between canopy and subcanopy habitats in the distribution of various sexual systems. Out of the 28 species subjected to controlled pollinations, 24 showed the presence of self‐incompatibility. The site of the incompatibility barrier in distylous species was either in the stigma or in the style. In most of the monomorphic species, the incompatibility barrier was in the ovary. Although a majority of tree species in the rain forest appear to be obligate outcrossers (xenogamons), the potential for inbreeding due to small effective population size still remains to be explored.
REPRODUCTIVE BIOLOGY OF TROPICAL LOWLAND RAIN FOREST TREES. II. POLLINATION SYSTEMS
Authors: Bawa K. S. , Bullock S. H. , Perry D. R. , Coville R. E. , Grayum M. H.
Published: January 2018

The reproductive biology of tree species of a tropical rain forest was investigated to determine the relative frequency and spatial distribution of different types of pollination mechanisms. Species pollinated by medium‐sized to large bees were most frequent, followed by those pollinated by moths, small diverse insects and small bees, in that order. Almost one half the total species were found to have pollinators with wide foraging ranges. Species pollinated by various groups of pollinators were distributed non‐randomly. The greatest diversity of pollination systems was found in the subcanopy. As compared to the subcanopy, pollination mechanisms in the canopy were monotonous, consisting primarily of species pollinated by bees and small diverse insects. The hummingbird‐ and sphingid moth‐pollinated species were found mainly in the subcanopy. The factors underlying the non‐random distribution of pollinators are discussed and the potential implications of such distribution on the forest structure are explored.
MORPHOLOGY AND ANATOMY OF THE LEAF OF COLEUS BLUMEI (LAMIACEAE)
Authors: Fisher David G.
Published: January 2018

Leaves of the Princeton and a variegated clone of Coleus blumei Benth. were examined with the light microscope to determine the course of their vasculature and the spatial relationship between the mesophyll, bundle sheath, and vascular tissues. In Princeton clone leaves two leaf traces enter the petiole at the node and quickly branch to form an arc of bundles which undergo further divisions as well as fusions in the distal half of the petiole. The anastomosing arc of bundles reaches its greatest complexity in the base of the midvein, where its lateral‐most bundles unite and diverge outward to form secondary veins. As the midvein bundles continue acropetally, they gradually fuse more and divide less until only a single bundle remains, from which secondaries and smaller veins branch. Major (ribbed) veins include not only the midvein and secondaries but also tertiary and quaternary veins. Decreasing vein size is accompanied by increasing direct contact between vascular and photosynthetic tissues. Minor veins, which make up 86% of the total vein length, are completely surrounded by photosynthetic bundle sheaths and mesophyll consisting of palisade and spongy parenchyma. Statoliths occur in a layer of cells just outside the phloem of the petiole‐midrib axis and secondary veins. Functional hydathodes are present at the apices of the marginal teeth. The overall organization of tissues in variegated leaves differs little in either the green or albuminous areas from corresponding (but always green) regions of Princeton leaves. Chloroplasts are lacking in mesophyll, bundle‐sheath, and most guard cells of the albuminous region but are present in guard cells which are within 1 mm of green areas.
STUDIES ON THE ROOT OF HORDEUM VULGARE L.– ULTRASTRUCTURE OF THE SEMINAL ROOT WITH SPECIAL REFERENCE TO THE PHLOEM
Authors: Warmbrodt Robert D.
Published: January 2018

Seminal root tissue of Hordeum vulgare L. var. Barsoy was fixed in glutaraldehyde and osmium tetroxide and studied with the light and electron microscopes. The roots consist of an epidermis, 6–7 layers of cortical cells, a uniseriate endodermis and a central vascular cylinder. Cytologically, the cortical and endodermal cells are similar except for the presence of tubular‐like invaginations of the plasmalemma, especially near the plasmodesmata, in the former. The vascular cylinder consists of a uniseriate pericycle surrounding 6–9 phloem strands occurring on alternating radii with an equal number of xylem bundles. The center of the root contains a single, late maturing metaxylem vessel element. Each phloem strand consists of one protophloem sieve element, two companion cells and 1–3 metaphloem sieve elements. The protophloem element and companion cells are contiguous with the pericycle. Metaphloem sieve elements are contiguous with companion cells and are separated from tracheary elements by xylem parenchyma cells. The protoplasts of contiguous cells of the root are joined by various numbers of cytoplasmic connections. With the exception of the pore‐plasmodesmata connections between sieve‐tube members and parenchymatic elements, the plasmodesmata between various cell types are similar in structure. The distribution of plasmodesmata supports a symplastic pathway for organic solute unloading and transport from the phloem to the cortex. Based on the arrangement of cell types and plasmodesmatal frequencies between various cell types of the root, the major symplastic pathway from sieve elements to cortex appears to be via the companion and xylem parenchyma cells.
HYPHAL WALL COMPOSITION OF MINDENIELLA SPINOSPORA AND ARAIOSPORA SP.
Authors: Bertke Charles C. , Aronson Jerome M.
Published: January 2018

Mechanically isolated hyphal walls of the rhipidiacean fungi Mindeniella spinospora Kanouse and Araiospora sp. (Oomycetes) were examined by biochemical, cytochemical and x‐ray diffraction analyses. In both fungi, the most abundant wall constituents were 1 → 3‐ and 1 → 6‐linked β‐glucans accounting for 91% of wall dry weight in M. spinospora and 87% in Araiospora sp. In addition, hyphal walls of M. spinospora contained 1.7% mannose, 4.3% protein, 2.0% ash and 1.0% lipid. The quantities of these components in Araiospora sp. were 1.9%, 1.8%, 1.5%, and 1.3%, respectively. Both species had cellulose contents ranging from one‐fifth to one‐fourth of wall dry weight and chitin was apparently absent. In general, wall composition of both fungi is quite similar to that of the related species Sapromyces elongatus, lending support to the assertion that a biochemical dichotomy exists with respect to hyphal wall composition between Rhipidiaceae and Leptomitaceae, the two families comprising the order Leptomitales.
GENETIC VARIATION IN THE HOMOSPOROUS FERN PELLAEA ANDROMEDIFOLIA
Authors: Gastony Gerald J. , Gottlieb L. D.
Published: January 2018

Genetic variability was examined in nine sexual and three apogamous natural populations of the homosporous fern Pellaea andromedifolia by electrophoretic analysis of enzymes specified by eight loci. Genetic interpretations of heterozygous banding patterns were determined by segregational analysis of gametophytes. High levels of segregating heterozygosity characterized the sexually reproducing populations, and genotype frequencies at the five polymorphic loci were consistent with those expected under conditions of random intergametophytic mating. Multiple‐banded patterns in the apogamously reproducing populations resembled those of heterozygous sexual individuals, but did not segregate. The results suggest that genetic variation in sexual homosporous vascular plants is produced by cross fertilization of genetically different gametes and may not result from pairing between homoeologous chromosomes carrying duplicated loci as previously thought.
THE RELATIONSHIPS BETWEEN SEASONAL VARIATION IN LIGHT INTENSITY, RAMET SIZE, AND SEXUAL REPRODUCTION IN NATURAL AND EXPERIMENTAL POPULATIONS OF ASTER ACUMINATUS (COMPOSITAE)
Authors: Pitelka Louis F. , Ashmun Jeffrey W. , Brown Robert L.
Published: January 2018

We conducted experiments to evaluate the effects of different patterns of seasonal light availability on ramet size and sexual reproduction in the understory herb, Aster acuminatus. In April 1982, 200 potted rhizomes were divided equally between a high light and a shaded site. Twice during the growing season subsets of pots were reciprocally transferred between the sites, resulting in eight different light treatments. There was significant variation among treatments in mean ramet weight (0.41–1.21 g), height (15.0–23.4 cm), number of flowers (0.4–7.9) and percentage of ramets flowering (14–95). Periods of high light increased ramet height, weight, rhizome production and flowering, but high light earlier in the season increased ramet height more than did high light later in the season, while high light later had pronounced effects on the other three traits. Measurements taken in nine natural patches experiencing different patterns of seasonal light availability are consistent with the experimental results. The results provide new insights into the general phenomenon of size‐dependent reproduction in herbs and illustrate how the phenology of biomass allocation can affect growth and reproduction.
ISOZYME VARIATION IN THE RACES OF MAIZE FROM MEXICO
Authors: Doebley John. F. , Goodman or M. , Stuber Charles W.
Published: January 2018

Twelve plants each of 94 collections of maize (Zea mays L. subsp. mays) representing 34 races from Mexico were analyzed for 13 enzyme systems encoded by 23 loci. This analysis revealed an exceptionally high level of variation within and among the races. We recorded an average of 7.09 alleles/locus and an expected heterozygosity of 0.182. Seventy‐two percent of the isozyme variation resided within collections, and 27% among collections. Races from northern and northwestern Mexico tend to possess higher levels of variation than those from the south. Variation for some isozyme alleles is strongly correlated with altitude. Maize is among the most variable species that have been studied isoenzymatically. Maize has levels of variation comparable to those found in its wild relatives, the teosintes. Principal component and cluster analyses showed continuous variation among the races with no well‐defined racial complexes; however, three weakly differentiated groups were apparent: 1) the high‐elevation Mexican pyramidal races, 2) the northern and northwestern races, and 3) most remaining races including the southern and western low‐elevation dent and flour corns.
DIFFERENTIAL ANTHERIDIOGEN RESPONSE AND EVOLUTIONARY MECHANISMS IN CYSTOPTERIS
Authors: Haufler Christopher H. , Ranker Thomas A.
Published: January 2018

It has been demonstrated that antheridiogens determine gametangial initiation in cultures of some homosporous fern gametophytes. Studies of natural populations have implicated these compounds as breeding system controllers. In Cystopteris, response to antheridiogen varied significantly among species. While Cystopteris protrusa responded to exogenous antheridiogen, C. bulbifera did not. The allopolyploid derivative of these two species, C. tennesseensis, had an intermediate level of response. This marked physiological difference among morphologically similar taxa is valuable in delineating species and suggests a mechanism that may be associated with interspecific hybridization.