bluuebunny/crossref_metadata_2025 huggingface dataset:
DEATH OF STEPPE CRYPTOGAMS UNDER THE ASH FROM MOUNT ST. HELENS
Authors: Harris Elaine , Mack Richard N. , Ku Maurice S. B.
Published: January 2018

Terrestrial mosses and lichens in the steppe of Washington were buried under volcanic ash from the 18 May 1980 eruption of Mount St. Helens. Unlike adult vascular plants in these communities, these cryptogams died following the deposition of silt‐size ash. Death within as little as four months was demonstrated by anatomical deterioration and these organisms' inability to fix CO2, to fluoresce in IR radiation, and to absorb vital stains. Although cryptogams in the steppe have probably been destroyed repeatedly by ash falls during the Holocene, this recent destruction is the first since the arrival of alien plants in the nineteenth century. Death of cryptogams may allow the initiation of further colonization by alien plants because a cryptogamic crust forms a barrier to seedling establishment.
EFFECT OF SEED DIMORPHISM ON THE DENSITY‐DEPENDENT DYNAMICS OF EXPERIMENTAL POPULATIONS OF ATRIPLEX TRIANGULARIS (CHENOPODIACEAE)
Authors: Ellison Aaron M.
Published: January 2018

The importance of seed size and density in determining individual plant performance and plant population dynamics in experimental populations of the halophyte Atriplex triangularis was studied. Two distinct seed morphs—large, light seeds and small, dark seeds—are produced by individual A. triangularis plants. Experimental populations consisting of seed size monocultures (large or small seeds) and seed size mixtures were established at three different densities, and the time of germination, plant size, plant survivorship, and plant fecundity were monitored. Marked variation in time of germination was observed among treatments and between seed sizes, but germination within any given treatment occurred over a five‐ to ten‐day period. Large seeds produced larger plants than small seeds did, and this dichotomy was maintained over the course of the entire experiment. Germination date and seed size interacted such that larger plants grew from seeds which germinated earlier than those which germinated later, regardless of seed size. Germination date had a more pronounced effect than seed size did on plant mortality in high density populations. At high density, large seed monocultures experienced greater mortality than small seed monocultures did, but in seed size mixtures, the mortality was evenly distributed between plants from the two seed sizes. Regardless of density conditions and parentage, large and small seeds were produced in equal proportion by the plants. Total seed production, however, was dramatically affected by plant density, and to a lesser degree by germination date. Although seed size effects alone did not appear to affect directly final plant biomass and fecundity, effects of seed size early in ontogeny may have contributed to differences in fecundity.
LEAF TYPES IN THE ARACEAE
Authors: Ray Thomas S.
Published: January 2018

Leaf types in the Araceae are described and classified on the basis of their morphology and functional role. Four classes are recognized on the basis of their association with the initiation of new shoot axes, the continuation of axes, the resting of axes, or the termination and renewal of axes. The basic types are described with the terms leaf, prophyll, mesophyll, bracteole, mesobracteole, cataphyll, and blastophyll. These terms are modified with the terms monopodial, sympodial, proleptic, sylleptic, resting, flagellar, stolon, reduced, and foliage. This represents an unconventional terminology because some of the modifiers refer to the structure of the stem to which the leaves are attached, rather than to the form of the leaf itself. The intent is to draw attention to the impact of shoot organization on leaf form, and to develop a leaf terminology that will aid in describing shoot organization.
XYLEM ANATOMY AND HYDRAULIC CONDUCTANCE OF PSILOTUM NUDUM
Authors: Schulte Paul J. , Gibson Arthur C. , Nobel Park S.
Published: January 2018

Psilotum nudum (L.) Beauv. (Psilotopsida) has a simple, vascularized sporophyte with a dichotomously branching aerial axis. The number and lumen diameters of tracheids in the actinostele decrease in each subsequent branch, leading to an approximate halving of the measured hydraulic conductance (Kh) from segment to segment. To understand how the anatomy of P. nudum affects Kh, a biophysical model based on the Hagen‐Poiseuille relation was developed that incorporated lumen diameter, tracheid taper, pit cavities, and pit membranes. Using a technique previously developed for ferns, pit membrane resistance was determined by measuring water flow before and after dissolving the pit membranes with cellulase. Measured Kh was in good agreement with Kh calculated with the model after excluding thick‐walled late metaxylem tracheids that dye studies showed were nonconducting. Model simulations showed that the approximately 40% overlap observed for tracheids of P. nudum was in the range leading to greatest conductance and that Kh decreased to half for 20% overlap. The model also showed that the pit membranes account for an increasing percentage of total resistance to water flow as the lumen diameter increases. Thus, the removal of such primary wall material and the evolutionary origin of vessels would have substantially increased Kh.
COMPARISON OF SHOOT APEX DYNAMICS AND EARLY LEAF ONTOGENY IN TWO SPECIES OF SARACA (LEGUMINOSAE)
Authors: Stein Otto L. , Johnson Claire M.
Published: January 2018

Shoot apices of Saraca indica produce adult leaves that have 4 to 6 pairs of leaflets, whereas those of S. bijuga usually have only 2 pairs. In both species one leaflet pair is found during the juvenile phase. Juvenility lasts many plastochrons in S. bijuga but is restricted to a few in S. indica. The shoot apical meristems of these two taxa are similar in structure, cell number, and cell size; however, the shoot apex of Saraca bijuga is slightly more stratified, having 2–3 tunica layers as opposed to 1–2 in S. indica. For most of the plastochron the apical meristem in both species is situated laterally at the base of the most recently formed leaf. A newly forming primordium and its internode shift the apical meristem upward unilaterally; the meristem passes through a brief apical dome stage and becomes positioned 180° from its origin at the beginning of the plastochron. Hence, there is a true pendulum meristem in both species. In S. bijuga the maximum length of the youngest leaf primordium, just prior to the formation of its successor, is twice that of S. indica. The internodes immediately below the shoot apex and the axillary buds develop more rapidly in S. bijuga than in S. indica. It is suggested that the bijugate leaf of S. bijuga represents a case of neoteny in plants.
LEAF HAIRS IN ENCELIA (ASTERACEAE)
Authors: Ehleringer J. R. , Cook C. S.
Published: January 2018

Four different kinds of leaf hairs occur in Encelia species. These are unicellular‐based and multicellular‐based uniseriate hairs, moniliform hairs, and biseriate glandular hairs. The unicellular‐based uniseriate hairs appear responsible for increased leaf spectral reflectance by species within the genus. In particular, it appears that elongation of the distal cell of the uniseriate hair is necessary for increased leaf reflectance.
EFFECTS OF FLOODING AND NUTRIENT ENRICHMENT ON BIOMASS ALLOCATION IN ACER RUBRUM SEEDLINGS
Authors: Day Frank P.
Published: January 2018

A greenhouse experiment was conducted on Acer rubrum seedlings to evaluate the effects of flood frequency on production and allocation of biomass and to test the effects of N and P fertilization on production and allocation. Seedlings from the Dismal Swamp were subjected to three flood treatments (no flooding, intermittent flooding, and continuous flooding) and four enrichment treatments (no enrichment, N additions, P additions, and N + P additions). More continuous flooding resulted in less biomass production. Biomass increased during the study in all treatments except for root mass in the continuously flooded treatment. However, production of abundant adventitious roots compensated for the lack of normal root growth. Root/shoot ratios exhibited the greatest decreases in the continuously flooded plants. Plants with N + P added had significantly more leaf, stem, and total mass than the nonenriched plants four months into the study. The N + P additions had apparently compensated for the effects of flood stress in the continuously flooded plants by the end of the study. The fertilized seedlings accumulated higher concentrations of N and P, but their nutrient use efficiency (biomass production per unit nutrient absorbed) was lower than in the nonenriched plants. Acer rubrum seedlings survive flooded conditions through several adaptations; however, theirgrowth is slowed by continuous flooding.
METABOLIC ASPECTS OF THERMOGENESIS IN MALE CONES OF FIVE CYCAD SPECIES
Authors: Tang William , Sternberg Leonel , Price David
Published: January 2018

High starch concentrations in the sporophylls of male cones of five species of cycad and their depletion during their heat‐producing phase of development suggest that starch is a major fuel source for thermogenesis in these plants. Carbon‐13/carbon‐12 ratio analyses of respired CO2, starch, and lipids in a male cone of one of these species, Macrozamia moorei F. Muell., indicate that although starch is a major contributor to respiration, lipids are also an important respiratory substrate.
INFLUENCE OF ENVIRONMENT AND POPULATION ORIGIN ON SURVIVORSHIP AND REPRODUCTION IN RECIPROCAL TRANSPLANTS OF AMPHICARPIC PEANUTGRASS (AMPHICARPUM PURSHII)
Authors: Cheplick Gregory P.
Published: January 2018

Reciprocal transplants of both seeds and seedlings were utilized to determine whether populations of the annual grass Amphicarpum purshii have become locally adapted to specific habitats due to the consistent production of cleistogamous subterranean seeds from year to year. The hypothesis was that subterranean seeds placed in the same habitat as the parents will produce seedlings of greater vigor and adults of higher reproductive capacity than plants from seeds transplanted to a different habitat far removed from the parents. For both seed and seedling transplant experiments involving three sites in the Pine Barrens of New Jersey, the effects of site on shoot dry weight and production of aerial spikelets, subterranean spikelets, and seeds were generally much more significant than the effects of population origin. With one exception, there was no tendency for seedlings (or plants from seeds) replanted into their home sites to outperform alien seedlings (or plants from seeds) transplanted into these same sites. The overriding importance of environmental factors (relative to genetic differences among populations) in determining the phenotypic expression of life history characters, and selection occurring during succession at a site may retard the evolution of genetic adaptation to local habitat conditions in this species.
ANAEROBIOSIS AS A STIMULUS TO GERMINATION IN TWO VERNAL POOL GRASSES
Authors: Keeley Jon E.
Published: January 2018

Tuctoria greenei and Orcuttia californica are two aquatic annual grasses in the small tribe Orcuttieae. They are endemic to seasonal pool habitats in California and Baja California. In years of poor rainfall their seed banks remain dormant until a season of rainfall which is adequate to fill the pool basins. This study attempts to elucidate the factors responsible for cuing germination. Tuctoria greenei germination is almost entirely dependent upon a combination of anaerobic conditions and light. It is suggested that in nature, such cues would be relatively specific to the uppermost soil substrate overlain by water. Orcuttia californica germination exhibits far less dependence upon anaerobic conditions. There is some indirect evidence that fungi may play an important role in stimulating germination of this species.
REASSIGNMENT OF ASPIDIUM HETEROPHYLLUM TO A NEW GENUS IN THE FAMILY M ATONI ACE AE
Authors: Skog Judith E.
Published: January 2018

A fossil fern described originally by W. Fontaine as Aspidium heterophyllum has been reexamined. Based upon characteristics of the sorus, indusium, sporangium, and spores the plant belongs to the family Matoniaceae. There is no genus within the family to which the fossil can be assigned; thus, a new genus (Delosorus) is proposed. This report increases the number of plants within the Lower Cretaceous Potomac Group that belong in the Matoniaceae.
CHROMOSOME NUMBERS AND THEIR SYSTEMATIC IMPLICATIONS IN HAWAIIAN LOBELIOIDEAE (CAMPANULACEAE)
Authors: Lammers Thomas G.
Published: January 2018

Chromosome numbers are reported for 20 collections of Hawaiian Lobelioideae (Campanulaceae), representing six genera, 13 species, and two interspecific hybrids. All are n = 14. Chromosome numbers are reported for the first time for eight species of Clermontia, Cyanea, Delissea, Lobelia, and Trematolobelia; the report for Delissea is the first for that genus. Additional determinations confirmed previously reported numbers in five other species of Brighamia, Clermontia, and Cyanea. Chromosome numbers are now known for all seven genera and 20 of the 110 species. All accepted counts are n = 14. It is suggested that all Hawaiian Lobelioideae share this number and are paleotetraploid. There is no evidence that the prolific speciation evident among these plants was accompanied by euploid or aneuploid change in chromosome number. The Hawaiian Lobelioideae, particularly the monophyletic lineage of 91 baccate species, offer further support for the generalization that change in chromosome number is an uncommon mode of speciation in insular floras.
GENE FLOW IN LICHENS
Authors: Culberson Chicita F. , Culberson William Louis , Johnson Anita
Published: January 2018

Experimental studies of the evolutionary biology of lichen fungi have been hampered by massive difficulties of in vitro culture and artificial crosses are still not possible. Gene flow in these organisms is demonstrated here for the first time by the analysis of secondary products in the progeny of individuals from natural populations of mixed chemotypes of the Cladonia chlorophaea complex. All of the chemotypes in this study have been interpreted as distinct sibling species. In the Appalachian Mountains of North Carolina, however, the grayi and merochlorophaea chemotypes are found to belong to a single interbreeding populations that is reproductively isolated from the cryptochlorophaea chemotype. In the Coastal Plain, the cryptochlorophaea chemotype hybridizes with the local endemic perlomera chemotype. This study has major impact for species concept in lichens because consideration of neither morphologial tendencies nor biogenetic relationships of the secondary products could have predicted its result.
COMPETITIVE RELATIONSHIPS OF OENOTHERA SPECIES WITH DIFFERENT RECOMBINATION SYSTEMS
Authors: Russell Joanna , Levin Donald A.
Published: January 2018

The hypothesis that outcrossers are competitively superior to close relatives with specialized genetic systems was tested. Interspecific competition between three closely related Oenothera species was examined in common garden environments. Oenothera grandis, an obligate outcrosser, is competitively superior to its derivative, O. laciniata, an obligate chromosomal heterozygote. Both of these species are superior to O. mexicana, a closely related facultative selfer. These relationships were consistent over two levels of density stress. Therefore, in this species triad, the outcrosser has a competitive advantage over its close relatives with derived breeding systems.
RESPONSE OF WOODY SWAMP SEEDLINGS TO FLOODING AND INCREASED WATER TEMPERATURES. I. GROWTH, BIOMASS, AND SURVIVORSHIP
Authors: Donovan Lisa A. , McLeod Kenneth W. , Sherrod K. C. , Stumpff Nancy J.
Published: January 2018

Growth, biomass, and survival of bald cypress (Taxodium distichum [L.] Richard), water tupelo (Nyssa aquatica L.), black willow (Salix nigra Marshall), and button bush (Cephalanthus occidentalis L.) were examined in a 3 times 3 factorial experiment varying water temperatures (AMBIENT, MID, and HIGH [~40 C]) and water levels (DRAINED, SATURATED, and FLOODED). Stem diameter and height, biomass, and survivorship for water tupelo and bald cypress were all reduced by the HIGH/FLOODED treatment. Black willow growth had the greatest variability among nonlethal flooding and temperature treatments, and achieved the greatest biomass of the four species. In the HIGH/FLOODED treatment, however, only 47% of the black willow seedlings survived and stem diameter, height, and biomass of survivors were greatly reduced. Button bush had intermediate variability of growth to the nonlethal treatments as compared to the other study species. Survival of button bush seedlings in the HIGH/FLOODED treatment was high (87%), but root biomass of the survivors was reduced. Interspecific differences in growth, biomass, survivorship, and morphological characteristics existed among these swamp species to experimental conditions. These responses may help explain vegetation patterns in a thermally impacted swamp.
DISPERSAL OF HETEROMORPHIC SEEDS IN AMPHICARPAEA BRACTEATA (FABACEAE)
Authors: Trapp E. Joseph
Published: January 2018

The dispersal of the chasmogamous, aerial cleistogamous, and subterranean cleistogamous seeds of Amphicarpaea bracteata was examined. The chasmogamous and aerial cleistogamous seeds are ballistically dispersed. Chasmogamous seeds were dispersed farther than the aerial cleistogamous seeds due to the height advantage of the chasmogamous pods. There was no difference in the firing angle or the initial velocity of the seeds discharged from the two aerial pod types. The subterranean cleistogamous seeds are “dispersed” the shortest distance by the elongation of runners. Differential dispersal of the three types of seeds may be a factor involved in the evolution of cleistogamy in A. bracteata.
HOMEOSIS IN PLANTS
Authors: Sattler Rolf
Published: January 2018

According to a broad definition, homeosis is the assumption by one part of an organism of likeness to another part. In developmental terms this means that at the site of one part another part or features of another part are expressed. Whereas homeosis continues to be actively investigated in animals, especially at the genetic level, it has been almost completely ignored or overlooked in plants. One purpose of this article is to draw attention to the fact that homeosis is widespread in plants from the cellular to the organismal level. Another purpose is to examine some of the consequences of this phenomenon for developmental and evolutionary plant biology, particularly homology, punctuated equilibra, and macroevolution.
SEXUAL DIMORPHISM IN BIOMASS ALLOCATION AND CLONAL GROWTH OF XANTHOXYLUM AMERICANUM
Authors: Popp James W. , Reinartz James A.
Published: January 2018

Reproduction can have a high resource cost. It has been suggested that greater investments in sexual reproduction by female dioecious plants leads to a lower rate of vegetative growth in females than in males. In this study, we investigated sexual dimorphism in biomass allocation and genet growth of the dioecious clonal shrub, northern prickly ash (Xanthoxylum americanum). The allocation of biomass over the course of one growing season to reproductive tissue, leaves, and growth of aboveground first‐year wood, was compared in 18 clones growing in fields and six clones in woods in southeastern Wisconsin during 1985 and 1986. In addition, the number of shoots per clone, and weight of nonfirst‐year wood (accumulated biomass) above‐ and below‐ground were estimated. In open field sites, male clones allocated more biomass to new wood and less to reproduction than females, although males allocated more to flowers alone. Accordingly, male clones had significantly more shoots and more accumulated biomass both above‐ and below‐ground than female clones. In the woods, where fruit set was near zero, there were few significant differences between male and female clones in either biomass allocation or accumulated biomass. These results support the hypothesis that the high resource investment in fruit production by females reduces their vegetative growth relative to males.
AEROBIOLOGY AND POLLEN CAPTURE OF ORCHARD‐GROWN PISTACIA VERA (ANACARDIACEAE)
Authors: Niklas Karl J. , Buchmann Stephen L.
Published: January 2018

The phenology of pollen release and pollen capture by Pistacia vera was studied in the field and laboratory respectively. Inflorescences of Pistacia vera were examined in a wind tunnel to determine whether the behavior of airborne conspecific pollen around receptive flowers differed as a result of changes in the shape and size of the inflorescence. In addition, the behavior of unclumped (single) and clumped pollen grains was studied to determine differences in the probability of their capture. Wind speeds within a commercial orchard during pollen shedding averaged 0.9–2.2 m/sec and atmospheric pollen concentrations were highest between 0900–1100 hr MST. Each of three stages in inflorescence development (defined on the basis of the number of exserted stigmas) was examined under identical ambient airflow conditions with equal concentrations of airborne pollen (1,000 grains/m3). The general pattern of pollen grain motion involves direct inertial collision by windward surfaces and by sedimentation of pollen onto leeward surfaces; clumped pollen rarely sedimented onto leeward surfaces. Small changes in ambient wind speed (0.5 m/sec to 1.0 m/sec) produced significant changes in the pattern of pollen motion around inflorescences and altered the number of pollen grains captured by leeward surfaces. Thus, wind pollination in P. vera is affected both by windspeed and by the shape or size of flower clusters. Differences in the behavior of clumped and unclumped pollen result from their inertial properties and responsiveness to local changes in the direction and speed of airflow. Unclumped pollen has a higher probability of being captured by leeward surfaces. The apparent insensitivity of pollen motion to differences in inflorescence size may ensure equitable pollination during the acropetal development of flowers.
ANDROMONOECY AND VARIATION IN PHENOTYPIC GENDER OF PASSIFLORA INCARNATA (PASSIFLORACEAE)
Authors: May Peter G. , Spears E. Eugene
Published: January 2018

We studied the perennial vine Passiflora incarnata Linnaeus (Passifloraceae) in Alachua County, Florida, from May to August 1983 to determine the breeding system and investigate seasonal changes in phenotypic gender of individual plants. Passiflora incarnata is an obligate outcrosser, incapable of self‐fertilization. The major pollinators were carpenter bees (Xylocopa sp.). The proportion of flowers setting fruit was not limited by pollinator service, but the weight of individual fruits and number of seeds/fruit was increased over naturally pollinated flowers by manually performing cross‐pollination. Morphological differences in style position among flowers caused some flowers to function primarily as males and others to function as hermaphrodites. Although some of the flowers that functioned as males set fruit when manually cross‐pollinated, the proportion of these male flowers capable of setting fruit was lower than the proportion of hermaphroditic flowers setting fruit when manually cross‐pollinated. Further, some male flowers had atrophied ovary and styles and were completely incapable of setting fruit. Passiflora incarnata is thus functionally andromonoecious. The relative production of male versus hermaphroditic flowers varied among individuals and over the course of the flowering season. Unmanipulated plants in the population became increasingly male‐biased in floral sex ratios as the reproductive season progressed. We attempted to modify phenotypic gender in experimental plants by limiting the ability of plants in some treatment groups to set fruit. Treatment groups significantly affected production of hermaphroditic flowers, but production of male flowers was not affected by treatment. Treatment did not significantly affect fruit weight, number of seeds per fruit or the percentage of hermaphroditic flowers that successfully matured fruit. These results suggest that andromonoecy in P. incarnata is a mechanism for adjusting allocation of reproductive effort to male and female function, and that maternal investment in this species is regulated primarily by varying production of hermaphroditic flowers.
REPRODUCTIVE BIOLOGY OF DIPLOID AND TRIPLOID APIOS AMERICANA (LEGUMINOSAE)
Authors: Bruneau Anne , Anderson Gregory J.
Published: January 2018

Apios americana Medicus (Leguminosae; Phaseoleae), a tuberous, herbaceous vine, consists of diploid and triploid clones which are morphologically nearly identical. Although A. americana is widespread in eastern North America and flowers profusely throughout its range, fruit set is low. In part, this is because populations north of Connecticut consist almost exclusively of sterile triploid individuals. Although triploid populations occur south of this region, diploids predominate. Fruit set is also low in diploids. We attribute this to partial self‐incompatibility and to a low rate of floral visits by leaf‐cutter bees (Megachile spp.), the only legitimate pollinator. Visitation is easily measured because flowers have a nonrepetitive explosive tripping mechanism which must be triggered by insects. In two Connecticut populations only 10% of 299 flowers were tripped, and on average only about one‐half of these set fruit. We conclude that A. americana maintains populations by vegetative propagation, but expands its range and retains variability through sexual reproduction of diploids.
GENETIC VARIATION AND POPULATION STRUCTURE IN THE FERN BLECHNUM SPICANT (BLECHNACEAE) FROM WESTERN NORTH AMERICA
Authors: Soltis Pamela S. , Soltis Douglas E.
Published: January 2018

Population genetic structure in the homosporous fern Blechnum spicant was analyzed in six populations from western North America. Each population was divided into approximately 10 m by 10 m subpopulations, and genetic variation within and among subpopulations was compared using enzyme electrophoresis and F statistics. These analyses indicated that there was no evidence of genetic structure in four of the six populations examined. However, significant genetic heterogeneity among subpopulations was observed for the other two populations. The genetic structure of these populations may be attributable, in part, to family structure resulting from high rates of intragametophytic selling and/or spatial patchiness in the distribution of individuals due to limited habitat availability in these areas. Outcrossing populations of B. spicant generally lack genetic structure, whereas the most highly inbreeding population maintains significant genetic structure. The information obtained in this investigation of population genetic structure in Blechnum spicant is consistent with data for angiosperms and gymnosperms. It appears that the outcrossing mating system and effective mechanism of spore dispersal in B. spicant may account for the general lack of genetic structure within populations of this species.
GERMINATION ECOPHYSIOLOGY OF HERBACEOUS PLANT SPECIES IN A TEMPERATE REGION
Authors: Baskin Carol C. , Baskin Jerry M.
Published: January 2018

Germination phenology data have been collected from 75 winter annuals, 49 summer annuals, 28 monocarpic perennials, and 122 polycarpic perennials, and experimental investigations of dormancy breaking and germination requirements have been conducted on 56 winter annuals, 32 summer annuals, 18 monocarpic perennials, and 73 polycarpic perennials. The purpose of these studies was to determine if there are correlations between the dormancy breaking and germination requirements of seeds and the germination phenology, life cycle type, habitat requirements, range of geographical distribution, and phylogenetic relationships of the species. Germination phenology is highly correlated with the responses of seeds to the yearly temperature cycle. Species with winter and summer annual life cycles have predictable germination characteristics, but monocarpic and polycarpic perennials do not. Several dormancy types may be found in a given habitat, and narrowly endemic and widely‐distributed species in the same genus may have similar germination characteristics. Within some families there is a tendency for a particular type of seed‐temperature response to be very important, but frequently this is related to the predominance of a given life cycle type in the family.
APOMIXIS IN EUPATORIUM TANACETIFOLIUM (COMPOSITAE)
Authors: Rozenblum Ester , Maldonado Sara , Waisman Celina E.
Published: January 2018

Cytogenetics and embryological studies of male sterility have been reported for the first time in Eupatorium tanacetifolium Gill, ex H. et A. (Gyptis pinnatifida Cass.). This species produces viable seeds but abnormal pollen that is not shed by the anthers. There are great abnormalities in karyokinesis and cytokinesis in microsporogenesis that result in irregular sporads formed by 5–10 cells of variable size, shape, and chromosome number. There is an irregular distribution of chromosomes, due to absence of regular pairing and disjunction, presence of chromatinic bridges in most of telophases, and to succesive aberrant cytokinesis without formation of cell plate and with variably oriented walls. The two chromatids of each chromosome presumably remain joined until the end of the process. Somatic chromosome number of 2n = 30 is reported for one population of this species, an apomict taxon of probable triploid origin. Embryo‐sac ontogeny is of the Antennaria type of diplospory, wherein embryo and endosperm development are parthenogenetic.
ANATOMY OF SOME LEAF GALLS OF ROSA WOODSII (ROSACEAE)
Authors: Krishnan Hari B. , Franceschi Vincent R.
Published: January 2018

Infection of Rosa woodsii by some members of the order Hymenoptera results in neoplasmic outgrowths on the leaves. One type of outgrowth produces a spherical swelling (leaf gall) while the other has extensive hair‐like proliferations (hairy gall). The anatomy and ultrastructure of these galls were examined by light microscopy and transmission electron microscopy. The leaf gall cells were considerably larger than normal cells, lacked well‐developed chloroplasts and were loosely arranged with prominent intercellular spaces. Vascular bundles were scattered throughout the gall tissue. The upper three cell layers of the leaf gall tissue resembles a periderm, having many suberin lamellae. The suberin lamellae were often traversed by pores which may represent incomplete plasmodesmata. Phenolic compounds were commonly seen both in the normal and gall cells. A layer of internal cells of the hairy galls have remarkably thickened cell walls, presumably due to the deposition of cellulosic substances. Unlike leaf galls, the epidermal cells of the hairy galls were not heavily cuticularized and no periderm was found. The hair‐like outgrowths present on the outer surface of these galls had a central vascular bundle. The epidermis of the outgrowths also had thickened cell walls, and trichomes occurred on the outer surface. The structural modifications brought about by the insect invasion in these two galls are compared and their roles in gall formation are discussed.
ECOLOGICAL CONSEQUENCES AND PHENOTYPIC CORRELATES OF PETAL SIZE VARIATION IN WILD RADISH, RAPHANUS SATIVUS (BRASSICACEAE)
Authors: Stanton Maureen L. , Preston Robert E.
Published: January 2018

In this paper we examine some ecological consequences and phenotypic correlates of flower size variation in wild radish, Raphanus sativus. Mean corolla diameter varied significantly among individuals within natural populations of R. sativus in California. On the average, almost 40% of flower biomass was allocated to corolla tissue. In field experiments, pollinator visitation increased significantly with corolla size. Large flowers also accumulated more nectar when pollinators were excluded from plants. In three populations, corolla size was positively correlated with allocation to pollen per flower (either anther weight or pollen grain number), but there was usually no phenotypic relationship between corolla size and several measures of female allocation (ovule number per flower, proportion fruit set, and total seed mass per fruit). Plants growing in the field produced fewer large flowers per unit of stem, and stem biomass was negatively related to corolla size for plants grown under controlled greenhouse conditions. Male and female fitness may covary differently with allocation to attractive floral features in species such as R. sativus, where seed production is often limited by resources rather than by pollen.
ULTRASTRUCTURAL AND HISTOCHEMICAL CHARACTERISTICS OF THE STIGMA OF CICER ARIETINUM
Authors: Baird Lisa Morrison , Turano Margaret Jorgensen , Webster Barbara D.
Published: January 2018

The stigma of Cicer arietinum L. cv. UC‐5, a self‐compatible legume, is comprised of a small central region of papillate cells which exhibit a localized surface secretion at the white bud stage of development, and of surrounding peripheral cells which lack surface secretion at the white bud stage and at anthesis. The cuticle of cells of the central region is thin and smooth and is displaced from subtending cells and fragmented as a result of secretory production. The cuticle of peripheral cells is thick and rugose. Although it is also displaced by secreted material, it is not disrupted during the white bud stage of development or at anthesis. The contents of central and peripheral papillate cells are similar. Cells are densely cytoplasmic, often with starch‐containing plastids. Mitochondria, Golgi bodies, and associated vesicles are abundant, along with strands of smooth and rough endoplasmic reticulum. The limited stigma surface area covered by the secretion may restrict pollen capture and retention. This limited area may partly account for the notably unsuccessful hybridization attempts to broaden the genetic base and to develop improved cultivars of Cicer.
STRUCTURAL CORRELATES OF IMBIBITIONAL INJURY IN TYPHA POLLEN
Authors: Sack Fred D. , Leopold A. Carl , Hoekstra Folkert A.
Published: January 2018

The ultrastructure of Typha latifolia pollen was examined as a function of pollen moisture content and incubation temperature, in order to identify possible lesions induced by imbibitional chilling. A syndrome of structural traits was found which characterizes damaged grains. Compared to viable grains, the protoplast of damaged pollen has a higher proportion of its volume occupied by vesicles, and less volume occupied by cytoplasm. Damaged grains also tend to have dilated cisternae of endoplasmic reticulum, larger starch grains and lipid bodies, poorly preserved mitochondria and membranes, and, sometimes, numerous electron‐dense globules associated with membranes. The percentage of grains exhibiting this damage syndrome correlates closely with the number of ungerminated grains in most samples, regardless of moisture content or incubation temperature.

Injury due to rapid imbibition from the dry state or to imbibitional chilling appear to be similar structurally, regardless of whether the stresses are imposed singly or together. The injury is not confined to one cell component (e.g., mitochondria), but may involve a generalized disruption of membranes. These results suggest that similar stress responses are elicited by imbibition from the dry state and by imbibitional chilling.
ANOMALOUS SOLITARY FLOWERS ON ANTHER‐DERIVED PLANTS OF POPULUS MAXIMOWICZII
Authors: Stoehr Michael U. , Zsuffa Louis , Eckenwalder James E.
Published: January 2018

In five of 66 anther‐derived plants of Populus maximowiczii Henry (Salicaceae) unusual flowers were observed at ages six to eight months. Most flowers were male, occurring singly in a terminal position, and were characterized by cup‐shaped, calyx‐like floral discs bearing 14 to 18 stamens. The anthers failed to dehisce but did contain a few pollen grains when observed after squashing. One flower had, in addition to a set of stamens, two stigmas emerging from undeveloped ovaries. These flowers in haploid or dihaploid plants are in some ways similar to ancestral flowers that have been hypothesized for the Salicaceae, and may give an indication of the evolutionary pathway in the genus Populus.
EFFECTS OF APEX REMOVAL AND NUTRIENT SUPPLEMENTATION ON BRANCHING AND SEED PRODUCTION IN THLASPI ARVENSE (BRASSICACEAE)
Authors: Benner Barbara L.
Published: January 2018

The shoot apex of a plant may be damaged by herbivory, weather conditions, or other factors, leading to growth of some axillary buds into branches. This alteration of branching pattern can affect the location and extent of seed production. I examined the effects of removal of the shoot apex and of mineral nutrient addition on branching and seed production in Thlaspi arvense. Individual plants received no, early, or late apex removal and no, early, or late nutrient addition in a two‐way factorial experiment. Apex removal led to greater production of secondary branches. Total seed weight per plant was higher for early‐ than late‐removal plants under all nutrient treatments, but intact controls produced the highest total weight of seeds in two of three nutrient treatments, because their seeds were heavier. Addition of nutrients increased the numbers of secondary branches, fruits, and seeds, and the average and total weight of seeds produced. Apex removal resulted in increased seed production only when it occurred early and when nutrients were added at the same time. Resource availability and plant phenology can be influential in determining the effects of apical damage on seed production, and their effects in combination may differ from their individual effects.
MORPHOLOGY AND DISPERSAL OF ONE‐ AND TWO‐SEEDED DIASPORES OF CRYPTANTHA FLAVA
Authors: Casper Brenda B. , Grant Bruce W.
Published: January 2018

The wind‐dispersed diaspore of the herbaceous perennial Cryptantha flava (Boraginaceae) consists of one, or occasionally two, nutlets (seeds) enclosed in a pubescent calyx. Physical characteristics of one‐ and two‐seeded diaspores and their rates of descent in still air were compared. Natural dispersal distances in the field of calyces containing 0, 1, or 2 seeds were also measured. Two‐seeded diaspores are wider at the ovary and have a greater total mass, a greater mass of the ovary, and a higher rate of descent in still air than one‐seeded diaspores. Under field conditions, however, there is no difference in how far calyces containing 0, 1, or 2 seeds disperse. Thus rate of descent is not a good predictor of relative dispersal distances in this species. Much of the dispersal in the field must occur as movement along the surface of the ground, and during such secondary dispersal, the greater width of two‐seeded diaspores may compensate for the potentially opposing effect of their greater mass.
SEX EXPRESSION OF GURANIA AND PSIGURIA (CUCURBITACEAE): NEOTROPICAL VINES THAT CHANGE SEX
Authors: Condon M. A. , Gilbert L. E.
Published: January 2018

Gurania and Psiguria, long thought to be dioecious, are actually monoecious; values of Gp, a quantitative measure of an individual's phenotypic gender, are bimodally distributed in natural populations. Individual vines undergo two kinds of sex change: size‐related and intraseasonal. Small (in diameter) plants produce only male flowers; only large plants produce female flowers. In favorable greenhouse situations, plants that reach large sizes switch from all male to female flowering; in poor conditions, the same genotypes remain vegetative or male, or switch back from female condition. Intraseasonal sex change occurs when plants initiate a predominantly female flowering episode with a few functional male inflorescences. Such protandrous vines are usually unisexual any point in time. Since neither type of sex change is obvious without long‐term observations, we suggest that other “dioecious” angiosperms should be more carefully studied.
POLLINATION AND SEED PRODUCTION IN IPOMOPSIS AGGREGATA: DIFFERENCES AMONG AND WITHIN FLOWER COLOR MORPHS
Authors: Elam Diane R. , Linhart Yan B.
Published: January 2018

The pollination of red, pink, and white color morphs of Ipomopsis aggregata was evaluated to assess whether ethological isolation based on pollinator color discrimination may occur. We observed animal visitors, assessed pollen delivery, seed set per fruit, percentage of flowers setting fruit, nectar production, and timing of flower opening for different color morphs in the Front Range of Colorado. Based on traditional zoophilous flower classifications, we expected hummingbirds to pollinate red‐flowered I. aggregata subsp. collina and hawkmoths to pollinate white‐flowered I. aggregata subsp. Candida. However, ethological isolation does not appear to occur among color morphs of I. aggregata in the Front Range. Hummingbirds visited red‐flowered plants in excess overall, and, to a lesser extent, so did hawkmoths. Both hummingbirds and hawkmoths visited all color morphs and probably transferred pollen among them. Pollen delivery data and a day‐night bagging experiment also suggest that pollinators do not necessarily behave as predicted by flower classifications. In addition, there is little evidence for major differences between red, white, and pink flowers in any aspects of reproductive biology. Indeed, most variation occurs within a given color morph.
CARBOHYDRATE AVAILABILITY, RESPIRATION, AND THE GROWTH OF KENAF (HIBISCUS CANNABINUS) UNDER MODERATE SALT STRESS
Authors: Curtis Peter S. , Zhong Hai Lin , Läuchli André , Pearcy Robert W.
Published: January 2018

Salt stress may impose osmotic and respiratory costs on nonhalophytes that limit the availability of carbohydrates for growth. This was examined in kenaf (Hibiscus cannabinus L.) by the analysis of soluble carbohydrates, starch, and respiration rates in mature and expanding leaves from plants exposed to moderate salt stress. Plants were grown for 35 days in solution culture at 1, 37, and 75 mM NaCl under greenhouse conditions. Total carbohydrates increased in mature and expanding leaves with increasing salinity. The majority of this increase was as starch. Mature leaf respiration also increased under salt stress. The net accumulation of non‐osmotically active carbohydrates in expanding leaves suggests that growth was not limited by the generation or availability of carbohydrates but rather by the ability of the plant to effectively utilize this substrate in osmotic adjustment and growth.
SEQUENCE OF XYLEM DIFFERENTIATION IN LEAVES OF CUPRESSACEAE
Authors: Quinn C. J. , Gadek P. A.
Published: January 2018

Protoxylem differentiates discontinuously within the leaf trace in members of the Cupressaceae sensu stricto, the first tracheid appearing at the apex of the procambial trace more or less concurrently with the differentiation of the first transfusion tracheids. Differentiation of both tissues then proceeds in a basipetal sequence within the lamina, although much more rapidly in the protoxylem than in the adjacent transfusion tissue. Protoxylem also develops acropetally from the proximal end of the procambial trace within the axis and into the decurrent leaf base. The ascending and descending protoxylem strands finally meet opposite or slightly below the resin canal near the point of attachment of the leaf. This distinctive pattern of development has been observed in a range of taxa and leaf types within the family. The taxonomic and adaptive significance of this character is discussed.
DIVISION OF THE GENERATIVE CELL AND LATE DEVELOPMENT IN THE MALE GAMETOPHYTE OF GINKGO BILOBA
Authors: Friedman William E. , Gifford Ernest M.
Published: January 2018

Division of the generative cell in the male gametophyte of Ginkgo biloba to yield the sterile cell and spermatogenous cell was examined in vivo and in vitro. Evidence is presented in support of a new interpretation of development in which the sterile cell and spermatogenous cell arise from an unusual anticlinal ringlike division of the generative cell. This type of cell division is only known to occur during antheridial development in leptosporangiate ferns and stomatal development among certain ferns in the Schizaeaceae and Polypodiaceae. The strong similarities in development and cell arrangement within the male gametophytes of cycads and Ginkgo suggest that division of the generative cell in cycads may be the same as in Ginkgo. Although the ringlike (conically annular) divisions in the antheridia of leptosporangiate ferns and the male gametophytes of Ginkgo (and probably cycads) are remarkably similar and result in the production of a central spermatogenous cell, it is conjectural as to whether these patterns represent a striking convergence or evolutionary homology.
STIGMA SURFACE SECRETIONS OF PENNISETUM AMERICANUM
Authors: Reger Bonnie J.
Published: January 2018

The stigma of Pennisetum americanum (L.) Leeke is of the dry type. Receptive surfaces of papillae are covered by an extracuticular proteinaceous secretion that has esterase activity. Permeability mapping of an intact stigma indicates that the papillate tips of trichome cells are especially penetrable. Numerous discontinuities of the cuticle probably allow passage of surface secretions and of water for pollen hydration. Comparison of pellicle and intracellular proteins by native polyacrylamide gel electrophoresis and analytical electrofocusing showed them to be different. One particular fraction that had esterase activity was a glycoprotein with a molecular weight of 180,000–200,000 daltons and an isoelectric focusing point of 7.5–8.0. This protein was a major component of the pellicle and may play a nonselective role in pollen capture.
PATTERNS OF FRUIT PRODUCTION IN A NEOTROPICAL ORCHID: POLLINATOR VS. RESOURCE LIMITATION
Authors: Zimmerman Jess K. , Aide T. Mitchell
Published: January 2018

Patterns of growth, and of flower and fruit production, were monitored over two years in a population of the orchid Aspasia principissa Reichb. f. in central Panama. Observations and experimental manipulations were used to determine the relative importance of pollinator and resource limitation on fruit production. Within a season, fruit production was limited by pollinator availability. Fruit set for hand‐pollinated flowers was over six times greater than that for naturally pollinated flowers. However, in plants that produced more than one fruit, fruit size declined in subsequent fruits, indicating that resources could limit seed production within a season. Plants producing fruits in 1986, on average, produced smaller shoots and inflorescences in 1987 relative to plants that flowered but produced no fruit in 1986. Thus, plants are likely to be resource limited over their lifetimes. Most individuals of reproductive size (82.5%) did not produce fruit over a three‐year period. The reproductive dominance of a few individuals in this population of Aspasia principissa may have important implications for understanding the population structure of the species and the high species diversity of orchids.