bluuebunny/crossref_metadata_2025 huggingface dataset:
MARSH PLANTS AS VECTORS IN TRACE METAL TRANSPORT IN OREGON TIDAL MARSHES
Authors: Gallagher John L. , Kibby Harold V.
Published: January 2018

The role of Pacific coast marsh plants as vectors in the flux of trace metals was studied in natural and perturbated situations. The flux of Cr, Cu, Fe, Mg, Sr, and Zn were studied in natural stands of Carex lyngbyei, Distichlis spicata, Potentilla pacifica, and Salicornia virginica. Seasonal fluxes of trace metals into the shoots of the living plants were measured as was their transfer to the dead plant community through mortality. Disappearance from the latter community (through fragmentation, leaching and excretion) was calculated. Seasonal data were summed to produce annual input‐output budgets. The flux varied from 3 mg/m2 for Cr in a stand of Potentilla pacifica to 15,000 mg/m2 for Fe in Carex lyngbyei.
TRACE METAL CYCLING IN THE U.S. COASTAL ZONE: A SYNTHESIS
Authors: Ragsdale Harvey L. , Thorhaug Anitra
Published: January 2018

This synthesis of trace element research in estuarine communities of the U.S. coastline and the Caribbean provides a summary applicable to the shoreline of the tropical and temperate regions of the world which have mangroves, kelp beds, riverine marshes and seagrass communities. An inventory of sediments and leaf tissues shows Mn and Fe to be the most highly concentrated elements with Hg and Cd present in lowest concentrations. Generally, trace element concentrations in roots are much higher than in leaves and other tissues above the sediment. Tissue to sediment concentration ratios show that Cd is most likely to be bioamplified and that Cu, Hg, Sr and Zn may have relatively high concentration ratios which can exceed unity. A conceptual model was constructed to integrate the forcing functions, compartmental couplings, and dynamics common to these estuarine systems. Seasonality is important for changes in some trace element concentrations in plants and litter. Trace element additions to water or sediment increased certain trace element concentrations in plants and dead organic matter. It is clear that estuarine plant communities serve as living filters of estuarine trace elements. However, increased knowledge of trace element cycling in estuarine systems and relationships between trace element concentrations in plants and the estuarine food chain is needed, particularly food chains to man. There is a need for structured long‐term estuarine research to allow direct comparison of results among estuarine study sites, to identify the similarity of population and system processes among estuaries and to define the geographical scale over which estuarine research results may be generalized.
MICROHABITAT AND STRUCTURAL VARIATION IN THE ASPICILIA DESERTORUM GROUP (LICHENIZED ASCOMYCETES)
Authors: Kunkel Gregory
Published: January 2018

Fruticose and crustose forms of Aspicilia desertorum (Kremp.) Meresch. are recorded from Western Colorado in microhabitats beneath snow patches and on exposed rock surfaces, respectively. For single populations, microenvironmental variation in substrate, temperature, light intensity and water availability is directly related to continuous morphological variation. Functional variation with habitat is evident in growth form, stage of apothecial development, calcium oxalate pruinosity, anatomical disposition of unidentified crystalline material, cortical anatomy and continuity, numbers of algal cells per unit weight of thallus, medullary anatomy, maximum thallus water content (or water‐holding capacity) and relative thickness of hyphal walls. These multivariate relationships define ecomorphological syndromes and a pattern of variation with parallels at a higher phytogeographic level.
LEAF ORIENTATION, RADIATION INTERCEPTION, AND NOCTURNAL ACIDITY INCREASES BY THE CAM PLANT AGAVE DESERTI (AGAVACEAE)
Authors: Woodhouse Robert M. , Williams John G. , Nobel Park S.
Published: January 2018

Both field measurements and a computer model were used to study the interception of photosynthetically active radiation (PAR) by Agave deserti (Engelm.), a desert CAM plant with a basal rosette of massive opaque leaves. PAR interception was determined in the winter and the summer for upper and lower leaf surfaces on a plant with about 60 leaves. Total daily PAR on the leaf surfaces was approximately 10 mol m‐2 for a winter day and 20 mol m‐2 for a summer day. For a PAR of 15 mol m‐2, the nocturnal increase in acidity was about 0.6 mol m‐2 for both leaf surfaces and various leaf orientations, except for the oldest most horizontal leaves where the increase was less than half as large. The acidity increase measured in the field was 90% saturated at 25 mol m‐2. Thus, daytime PAR in the desert is often limiting for the nocturnal acidity increase, especially for the lower leaf surfaces. Simulated tilting of the plant by 55° so that the vertical axis pointed to the sun at solar noon on a winter day increased the PAR incident on the upper surfaces of the leaves, but did not affect the total nocturnal increase in acidity by the whole plant. Although simulated removal of alternate leaves increased the PAR per unit leaf area for the remaining leaves, it reduced the total increase in nocturnal acidity of the whole plant by 31%. PAR interception by plants on slopes facing steeply north, east, or west was substantially reduced compared to the horizontal. Thus, the model proved to be quite useful for quantifying the relation between leaf orientation, PAR interception, and nocturnal increases in acidity by A. deserti, and it indicated that the lower frequency of plants on north‐ compared to south‐facing slopes was due to PAR limitations.
C3‐C4 PHOTOSYNTHESIS IN THE GENUS MOLLUGO: STRUCTURE, PHYSIOLOGY AND EVOLUTION OF INTERMEDIATE CHARACTERISTICS
Authors: Kennedy Robert A. , Eastburn Judith L. , Jensen Kenneth G.
Published: January 2018

The genus Mollugo has been reported to have species which are C4 plants and a C3‐C4 intermediate. In the present paper, we report on the anatomy and photosynthetic physiology of three additional species in the Molluginaceae, M. pentaphylla, M. nudicaulis, and M. lotoides, all of which possess some anatomical and physiological features of both C3 and C4 plants. Most notable among the variable C3‐C4 features are C4‐like bundle sheath cells, along with a C3‐like arrangement of palisade and spongy parenchyma. M. nudicaulis appeared to have lower photorespiration based on its CO2 compensation point and lower oxygen sensitivity of photosynthesis. The occurrence of polyploidy within this group of plants and its relationship to lower photorespiration or evolution of these species is discussed.
RESPONSES OF POPULATIONS OF SOLIDAGO SEMPERVIRENS (COMPOSITAE) TO SALT SPRAY ACROSS A BARRIER BEACH
Authors: Cartica Robert J. , Quinn James A.
Published: January 2018

The responses of four populations of Solidago sempervirens to salt spray at Island Beach State Park, a barrier beach in Ocean County, New Jersey, were examined under both field and greenhouse conditions. At increasing distances from the ocean, these populations were Primary Dune (PD), Dune Hollow (DH), Intermediate (INT), and Bayshore (BAY). Salt deposition on cheesecloth traps was found to drop significantly from PD to BAY. Population responses to the salt spray gradient were monitored by examining leaf stomatal and trichome densities, leaf thickness, and the salt spray tolerance of genotypes established in the greenhouse. No significant differences in either stomatal or trichome density were found among populations in the field. Leaf thickness of field plants at the PD site was significantly greater than the DH, INT, or BAY plants: however, unsprayed plants of these populations in the greenhouse did not vary significantly in leaf thickness, and for sprayed plants, leaf thickness varied only in relation to intensity of salt application. Thus, the differences in leaf thickness of field populations were not genetically based. Both nonexpanded and fully expanded leaves of BAY plants consistently showed the greatest percentage leaf damage following both low‐ and high‐intensity artificial salt spray, indicating possible selection for population differences in salt spray tolerance.
TISSUE LONGEVITY OF THE ARBORESCENT MONOCOTYLEDON, KINGIA AUSTRALIS (XANTHORRHOEACEAE)
Authors: Lamont Byron B.
Published: January 2018

Histochemical tests for tissue viability and microscopic examination of stem fragments of known age showed that the pith parenchyma of Kingia australis may survive for over 400 years. The longevity of phloem appears much lower, but 32P translocation studies indicate that this may still exceed 100 years. Explanations for such extreme longevity of adult tissue are suggested.
HERMAPHRODITIC FLOWERING IN GAMBEL OAK
Authors: Tucker J. M. , Neilson R. P. , Wullstein L. H.
Published: January 2018

Gambel oak (Quercus gambelii Nutt.) is normally monoecious, flowering once a year in spring. In Utah, August 1978, several individuals were observed producing hermaphroditic flowers in riparian habitats. This unusual event was preceded by a general freeze of male catkins in May which resulted in low acorn production. In 1979 the same individuals flowered normally, with no evidence of freeze damage or hermaphroditic flowers being observed. Acorns were produced on these individuals in both years. It is suggested that hermaphroditic flowering in the Fagaceae is an ancestral condition, still present in the genome, but normally suppressed, which may be evoked by unusual environmental conditions.
POPULATION BIOLOGY OF AVENA. VIII. COLONIZATION EXPERIMENT AS A TEST OF THE ROLE OF NATURAL SELECTION IN POPULATION DIVERGENCE
Authors: Jain S. K. , Rai K. N.
Published: January 2018

Artificially founded colonies of Avena barbata were utilized in two experiments in order to examine the role of natural selection in the evolution of regional differentiation in Central California. One experiment involved a total of 41 colonies founded in three different areas and scored over a 10‐yr period; these colonies, started with known genotypes, showed that although both Valley and Bay region genotypes establish successful colonies, their relative survivorship and fecundity suggests weak selective forces consistent with those predicted from the observed patterns in natural populations. The second experiment involved two localities, representing two climatic regimes of temperature, in each of which ten colonies were started from identical seed sources. These colonies also showed relatively higher fitness of the genotypes matching with those sampled from the Valley and Coastal regions, respectively, again in line with their regional pattern of distribution. Colonization experiments appeared to be useful even as short‐term in situ tests of certain specific evolutionary hypotheses on the role and intensity of natural selection.
OBSERVATIONS ON SYNAPTONEMAL COMPLEXES IN PREMEIOTIC INTERPHASE OF WHEAT
Authors: McQuade H. A. , Pickles D. G.
Published: January 2018

Synaptonemal complexes (SCs) were found in stage 3, premeiotic (S phase) pollen mother cell (PMC) nuclei of wheat which were labeled with 3H‐thymidine. Three nucleoli are present in PMC nuclei at the beginning of stage 3, premeiotic interphase (S3). During S3, nucleoli move toward the nuclear envelope and fuse to form one nucleolus near the end of the stage. PMC nuclei labeled with 3H‐thymidine were serially sectioned to show that more than one nucleolus was present and that SCs were also present in these DNA synthetic nuclei. Entire S3 PMC nuclei were serially sectioned to show the presence of SCs and all three nucleoli. Entire leptotene nuclei were also serially sectioned and segments of SCs were found. It is concluded that the association of homologous chromosomes in S3 of wheat is an early step in SC formation which proceeds through leptotene and is completed in zygotene and pachytene. Thus there is evidence that the continuum of chromosome pairing in wheat starts much earlier than was once thought.
GENOME RELATIONS OF AGROPYRON SERICEUM, HORDEUM JUBATUM AND THEIR HYBRIDS
Authors: Murry Lynn E. , Tai William
Published: January 2018

Cytogenetic investigation of microsporogenesis in Agropyron sericeum, Hordeum jubatum, their spontaneous hybrid, Agrohordeum pilosilemma, its amphiploid, and the backcross of the amphiploid to A. sericeum, B1, elucidated the genome relationships of A. sericeum and H. jubatum. The tetraploid parental species share a partially homologous genome which affects the pairing relationships evidenced in their hybrids. The genome formulae assigned to these plants are: A. sericeum, A“A”BB; H. jubatum, AAA'A‘; Agrohordeum pilosilemma, AA'A“B; the amphiploid, AAA'A‘A”A“BB; and B1, AA'A”A“BB. Observed pairing configurations were compatible with the expected maximum pairing configurations predicted under the assumption of genetic control of pairing with dosage effects. This is interpreted as further support for the hypothesis that pairing in the hybrids of H. jubatum is controlled by the A genome, one dose of A allowing homeologous pairing and two doses of A promoting homeologous association.
PHYSIOLOGICAL CONTROL OF CHAMISE SHOOT GROWTH AFTER FIRE
Authors: Radosevich S. R. , Conard S. G.
Published: January 2018

Five controlled burns (ca. 2 ha each) were conducted in the Coast Range of northern California near Hopland, California, between November 18, 1975 and September 15, 1976 to determine the effect of shrub phenology on the sprouting response of chamise (Adenostoma fasciculatum H&A) following fire. The time of burn had little effect on the amount of shoot growth that occurred after fire, although the pattern of growth was altered. Shrubs burned on June 22 or August 2, 1976 grew continually until August 1977, while unburned shrubs or those burned at other times ceased seasonal growth during the first summer after fire. Neither the amount nor the pattern of shoot growth was influenced by the shrub water status before the fire occurred. The relationship between chamise shoot growth after fire, 14CO2 fixation, xylem sap tension, and air temperature was also studied. The growth rate of regrowing shrubs was highly correlated with 14CO2 fixation prior to the growth measurement. Water status (pre‐dawn xylem sap tension) had a negative correlation with 14CO2 fixation. The abundance of carbohydrate at the shoot apex is believed to influence the seasonal pattern and rate of chamise shoot growth following fire.
FIELD AND GREENHOUSE INVESTIGATIONS OF THE EFFECT OF INCREASING SALT STRESS ON THE ANATOMY OF JAUMEA CARNOSA (ASTERACEAE), A SALT MARSH SPECIES
Authors: Omer Lucy St. , Schlesinger William H.
Published: January 2018

The effects of salt stress on water balance, growth and anatomy of Jaumea carnosa (Asteraceae) were investigated under field conditions and in greenhouse hydroponic culture experiments. In salt marshes near Santa Barbara, California, soil salinities at root zone varied from 0.37–2.33 osmoles during a 1‐yr study period. These salinities were used to plan hydroponic experiments in a nested experimental design of five salinity treatments. The plants were propagated from rhizome cuttings and were grown in aerated full‐strength Hoagland's solution plus varying amounts of NaCl (range 0.0–2.0 osmoles). Optimum growth was recorded at 0.3 NaCl osmole and the limit of salt tolerance was between 1.2 and 2.0 osmoles. The range of salinity tolerance established for the species in hydroponic experiments was very similar to the range recorded in the root zone in field samples. Dry matter production was significantly lower in plants grown without NaCl than in those grown at 0.3 NaCl osmole. There were no significant differences in saturation water deficit between plants grown at 0.3 and 0.6 NaCl osmole, but the saturation water deficit in plants grown at 1.2 NaCl osmoles was significantly higher than that of plants grown at the lower salt concentrations. As salinity increased both in field conditions and in hydroponic experiments, measurements of anatomical features revealed changes in few of the structural features often associated with salinity stress. With increasing salt concentrations, decreases in internodal length, leaf area, cell size, and stomatal frequency were measured. Diameter of the internode and stele, and thickness of the leaf and stem cuticle showed no significant variations under conditions of increasing salinities. In field samples significant increases in salt concentrations at the root zone during the study did not result in significant increases in leaf succulence. Similarly there were no corresponding increases in leaf succulence with increasing salt concentrations in the hydroponic culture experiments.
EVOLUTION IN CALIFORNIA POPULATIONS OF DIPLOID AND OCTOPLOID FRAGARIA (ROSACEAE): A COMPARISON
Authors: Hancock J. F. , Bringhurst R. S.
Published: January 2018

Genetic differentiation, physiological homeostasis, and heterozygosity were contrasted in the closely related octoploid species Fragaria chiloensis and F. virginiana, and in one of their putative diploid progenitors F. vesca. Plants from 27 natural sites supporting strawberry colonies were collected and grown in a common greenhouse. They were analyzed for 18 quantitative traits and three enzyme loci. Intra‐ and inter‐populational variation was measured using analysis of variance techniques. Micro‐ and macro‐environmental measurements were made at each site. Phenotypic stability of octoploid and diploid individuals was contrasted across four environmental regimes. The octoploids displayed more morphological variation, were more heterozygous, had greater physiological homeostasis, and were found across a broader range of environments. Octoploid strawberries may have broader ecological ranges than the diploids, both because they have higher levels of physiological homeostasis, and also because they have undergone more genetic differentiation. The higher levels of physiological homeostasis may be due to the fact that they are more heterozygous than the diploids.
ONTOGENETIC AND EVOLUTIONARY IMPLICATIONS OF A NEOTENOUS EXINE IN TAPEINOCHILOS (ZINGIBERALES: COSTACEAE) POLLEN
Authors: Stone Donald E. , Sellers Susan C. , Kress W. John
Published: January 2018

Tapeinochilos pollen, like that of most angiosperms, is spared by the standard acetolysis treatment because the sporoderm is impregnated with sporopollenin. This genus and its allies in the Costaceae are the only taxa in the eight families of Zingiberales that have acetolysis‐resistant pollen. The sporoderm in most of the order is characterized by exine reduced to a wispy coating or layer with delicately anchored spinules and a highly elaborated intine. Ultrastructural studies on the pollen of Tapeinochilos reveal a pattern of wall development that is significantly different from the generalized angiosperm type; namely, there are no columellae, nor is there any significant accretion of sporopollenin following the dissolution of callose and release of microspores. The primexine is composed of rodlets which build up solidly between apertures and become packed into layers to form a thick, stratified exinous covering. No secondary exine develops during the free spore period and the juvenile primexine persists as the protective coat on the mature pollen grain. This pattern of pollen development is viewed as an example of neoteny in which a juvenile or immature character is retained in adulthood.
EXTRAFLORAL NECTARIES AND PLANT GUARDING IN IPOMOEA PANDURATA (L.) G. F. W. MEY. (CONVOLVULACEAE)
Authors: Beckmann Robert L. , Stucky Jon M.
Published: January 2018

Throughout the range of Ipomoea pandurata in North and South Carolina, ants and wasps are attracted to the pedicellar extrafloral nectaries. These hymenopterans are aggressive toward phytophagous insects that visit the plants. Protection of the plant is afforded by these pugnacious hymenopteran nectar feeders.
FACTORS AFFECTING THE TOXICITY OF SEVERAL LICHEN ACIDS: EFFECT OF PH AND LICHEN ACID CONCENTRATION
Authors: Gardner Charles R. , Mueller Dale M. J.
Published: January 2018

The effect of pH 5–8 and lichen acid concentration gradients (2.7 times 10−2 ‐ 2.7 times 10−6 m) on the toxicity of the following lichen acids: usnic, lecanoric, evernic, vulpinic, stictic, fumarpro‐tocetraric, psoromic, and atranorin, on spores of Funaria hygrometrica was tested. Percent germination and sporeling growth were used as indicators of toxicity. None of the lichen acids were significantly toxic, for either percent germination or sporeling growth at concentrations equal to or below 2.7 times 10−5 m at pH 7.0, but many of the lichen acids which increased in toxicity at values different from pH 7 may have been toxic at lower concentrations if a different pH was used for the assay. Lichen acid toxicity showed a good correlation with pH for the parameter of spore germination, or sporeling growth, or both. Some lichen acids did not inhibit germination but were effective in retarding sporeling growth, or vice versa. This observation is discussed in relation to changing fatty acids and other lipid composition as germination occurs. Two of the three O‐methylated lichen acids (evernic and psoromic) were among the most effective in inhibiting growth over all, but at lower pH values these were less effective than non‐O‐methylated lichen acids. Stictic, which is also an O‐methylated lichen acid, was the least effective inhibitor over all the pH values for both parameters, while vulpinic was the most toxic over all the pH values. The order of relative toxicity for the lichen acids is different, depending on the pH and concentration at which they are tested and depending on the parameter measured. Thus, in an ecological sense, it is difficult to evaluate the adaptive significance of a particular compound or group of compounds without knowing what factors influence the toxicity of those compounds and how these factors vary in the organism's habitat.
RELATIONSHIPS AMONG SHOOT APICAL MERISTEM ONTOGENIC FEATURES IN TRICHOCEREUS PACHANOI AND MELOCACTUS MATANZANUS (CACTACEAE)
Authors: Niklas Karl J. , Mauseth James D.
Published: January 2018

Various morphometric parameters of shoot apical meristems were measured during the ontogeny of Melocactus matanzanus and Trichocereus pachanoi. While some ontogenic features varied dramatically (i.e., apical surface curvature, dK/dl, varied by 0.15–0.17, while the apical volume increased from 105 μm3 to 107 or 108 μm3), the percent volume of the central‐mother‐cell zone (CMCZ), pith‐rib meristem (PRM), and the peripheral zone (PZ) showed remarkable intraspecific constancy: CMCZ = 9.2%, PRM = 10.4%, PZ = 80% for M. matanzanus, and CMCZ = 10%, PRM = 24.5%, PZ = 65% for T. pachanoi. Seedlings (2 plastochrons old) showed distinctly different percent volumes from older forms: CMCZ = 7.8%, PRM = 5.9%, PZ = 86% for M. matanzanus, and CMCZ = 8.9%, PRM = 13%, PZ = 77% for T. pachanoi. Geometric expressions of cell patterns within zones of the apex remained relatively constant throughout development. On the basis of intra‐ and interspecific comparisons of the percent volumes among 23 taxa and the chronology in the appearance of zones within the apex, it is concluded that while there are no apparent biological reasons for the actual percent volume values computed from our sample set, the constancy in zones reflects a high degree of homeostasis which is achieved early in ontogeny.
COMPARISON OF THE VEGETATION OF THREE LOUISIANA SWAMP SITES WITH DIFFERENT FLOODING REGIMES
Authors: Conner William H. , Gosselink James G. , Parrondo Roland T.
Published: January 2018

Net primary productivity and community structure were studied at three adjacent swamp sites that were all once subject to seasonal flooding. Because of man‐related activities one is now permanently flooded, and a second is managed on a summer‐fall dry period and a winter‐spring flooded period. In the permanently flooded area such flood‐intolerant trees as green ash are dying while shrubs and aquatic plants are increasing. Competition among overstory trees is reduced, enhancing growth of existing baldcypress and water tupelo trees. Total areal production, however, is low (887 g/m2/yr) because of fewer trees. Productivity in the managed area is high (1,780 g/m2/yr). The baldcypress‐water tupelo community is being replaced by a swamp maple‐ash community typical of bottomlands. In the natural swamp forest, baldcypress and water tupelo have remained dominant. Canopy closure has limited understory and aquatic growth but has also increased competition among overstory trees, resulting in a slow increase in basal area. Productivity is about 1,166 g/m2/yr. It is suggested that the flooding regime is an important controlling factor in each of the areas.
THE YELLOW‐PIGMENTED DICTYOSTELIA
Authors: Cavender James C. , Worley Ann C. , Raper Kenneth B.
Published: January 2018

The cellular slime molds described herein are of a clear golden yellow color and belong to two naturally occurring groups. One we call Dictyostelium mexicanum sp. n. because it is found in soils from various parts of tropical and subtropical Mexico. The well‐tapered stalk and disklike base are somewhat reminiscent of D. discoideum. The other is regarded as D. aureum E. W. Olive (1901) with which we feel it is closely identified if not identical. In the latter group the form of both the aggregation and sorocarp is suggestive of D. mucoroides. Some less pigmented isolates are separated as D. aureum var. luteolum var. n.
POLLINATION ECOLOGY OF MONARDA DIDYMA, M. CLINOPODIA, AND HYBRIDS (LAMIACEAE) IN THE SOUTHERN APPALACHIAN MOUNTAINS
Authors: Whitten W. Mark
Published: January 2018

Monarda didyma L. and M. clinopodia L. occasionally form introgressive populations in the mountains of eastern Tennessee and western North Carolina. Monarda didyma produces large red scentless nectar‐rich flowers and is pollinated primarily by the Ruby‐throated Hummingbird (Archilochus colubris [Linnaeus]). The smaller, white, scented flowers of Monarda clinopodia produce small amounts of nectar and are pollinated mainly by bumblebees (Bombus spp.). The two species are highly interfertile and have strongly overlapping flowering periods. Differences in pollinator sets and pollinator constancy appear to be only partial barriers to hybridization. Lack of suitable habitats for the establishment of hybrid progeny might be the most important isolating mechanism between the two species.
INFLORESCENCE AND FLORAL DEVELOPMENT IN HOUTTUYNIA CORDATA (SAURURACEAE)
Authors: Tucker Shirley C.
Published: January 2018

The inflorescence of Houttuynia cordata produces 45–70 sessile bracteate flowers in acropetal succession. The inflorescence apical meristem has a mantle‐core configuration and produces “common” or uncommitted primordia, each of which bifurcates to form a floral apex above, a bract primordium below. This pattern of organogenesis is similar to that in another saururaceous plant, Saururus cernuus. Exceptions to this unusual development, however, occur in H. cordata at the beginning of inflorescence activity when four to eight petaloid bract primordia are initiated before the initiation of floral apices in their axils. “Common” primordia also are lacking toward the cessation of inflorescence apical activity in H. cordata when primordia become bracts which may precede the initiation of an axillary floral apex. Many of these last‐formed bracts are sterile. The inflorescence terminates with maturation of the meristem as an apical residuum. No terminal flowers or terminal gynoecia were found, although subterminal gynoecia or flowers in subterminal position may overtop the actual apex and obscure it. Individual flowers have a tricarpellate syncarpous gynoecium and three stamens adnate to the carpels; petals and sepals are lacking. The order of succession of organs is: two lateral stamens, median stamen, two lateral carpels, median carpel. The three carpel primordia almost immediately are elevated as part of a gynoecial ring by zonal growth of the receptacle below the attachment of the carpels. The same growth elevates the stamen bases so that they appear adnate to the carpels. The trimerous condition in Houttuynia is the result of paired or solitary initiations rather than trimerous whorls. Symmetry is bilateral and zygomorphic rather than radial. No evidence of spiral arrangement in the flower was found.
EVIDENCE FOR COMPETITIVE RELEASE IN SIMPLIFIED SAXICOLOUS LICHEN COMMUNITIES
Authors: Lawrey James D.
Published: January 2018

Saxicolous cryptogam communities were sampled quantitatively on two Potomac River island habitats in June of 1980. As a result of air pollution stress, the community on one island was found to be much simpler than that found on the other island. Two relatively pollution‐tolerant foliose lichen species, Xanthoparmelia conspersa and Pseudoparmelia baltimorensis, were found to dominate the communities on both islands. An examination of niche breadth and position along a light intensity gradient demonstrated that P. baltimorensis was most frequent at low light intensities and X. conspersa was most frequent at high light intensities. However, X. conspersa exhibited a niche shift toward intermediate light intensities in the species‐poor community, likely the result of reduced competitor diversity in this community since the intermediate light intensities supported the greatest number of species in the species‐rich community. Niche overlap between the two species was found to occur at lower light intensities in the species‐poor community, suggesting that X. conspersa is more likely to appropriate intermediate light intensities in this community. The significance of competition as a regulatory factor in lichen communities has not been fully appreciated. Since lichens and other cryptogams are frequently used as indicators of environmental quality, competitive processes in naturally occurring lichen communities must be thoroughly understood before changes in species distribution that apparently result from disturbance can be properly interpreted.
CHROMOSOME COUNTS, CYTOLOGY, AND REPRODUCTION IN THE CACTACEAE
Authors: Ross Robert
Published: January 2018

Chromosome counts and observations of reproduction for 55 taxa of Cactaceae indicate that polyploidy is correlated with self‐fertility, adventive embryony, profuse branching, and vegetative reproduction. Six genera (Blossfeldia. Cleistocactus, Frailea, Pelecyphora, Rebutia, and Strombocactus) and 35 species or varieties are reported here for the first time. Preliminary observations of pachytene and diplotene indicate that these stages may be more useful in chromosome recognition than mitotic stages. Secondary association at metaphase I and II is interpreted as a retention of homologue association at interphase I and II (interkinesis). During meiosis of certain species, Feulgen negative bodies are present. The production of an abnormal premeiotic division is suggested as a mechanism for polyploid origin.
LIGHT, TEMPERATURE AND SALINITY EFFECTS ON GROWTH, LEAF ANATOMY AND PHOTOSYNTHESIS OF DISTICHLIS SPICATA (L.) GREENE
Authors: Kemp Paul R. , Cunningham Gary L.
Published: January 2018

The effects of light, temperature, and salinity on growth, net CO2 exchange and leaf anatomy of Distichlis spicata were investigated in controlled environment chambers. When plants were grown at low light, growth rates were significantly reduced by high substrate salinity or low temperature. However, when plants were grown at high light, growth rates were not significantly affected by temperature or salinity. The capacity for high light to overcome depressed growth at high salinity cannot be explained completely by rates of net photosynthesis, since high salinity caused decreases in net photosynthesis at all environmental conditions. This salinity‐induced decrease in net photosynthesis was caused largely by stomatal closure, although plants grown at low temperature and low light showed significant increases in internal leaf resistance to CO2 exchange. Increased salinity resulted in generally thicker leaves with lower stomatal density but no significant differences in the ratio of mesophyll cell surface area to leaf area. Salinity and light during growth did not significantly affect rates of dark respiration. The mechanisms by which Distichlis spicata tolerates salt appear to be closely coulpled to the utilization of light energy. Salt‐induced leaf succulence is of questionable importance to gas exchange at high salinity in this C4 species.
POST‐FIRE REGENERATION OF SOUTHERN CALIFORNIA CHAPARRAL
Authors: Keeley Jon E. , Keeley Sterling C.
Published: January 2018

Succession of chaparral shrubs was studied for the first 4 years after fire on the four major slope faces at three elevations in southern California. Although total cover fluctuated from year to year, shrub cover increased annually through the third year. There was little or no increase in shrub cover between the third and fourth years. Four years after fire the shrubs covered 55% ground surface at the highest elevation site but only 28% at the lowest elevation site. Shrub cover was similar between slope faces with one exception; at the lowest elevation site shrub cover was twice as great on the north and east‐facing slopes as on the south and west‐facing slopes. Post‐fire recovery of shrubs was by seedlings and/or resprouts. Yucca whipplei was an exception in that it did not resprout once the aboveground parts were killed nor did seedlings establish after fire, however the aboveground parts of many Y. whipplei survived the fire. Species which reproduced entirely by seed did so in the first post‐fire year from soil‐stored seed with the exception of Ceanothus greggii at the highest elevation site. This species was entirely absent the first year after fire but abundant in the second year. Species producing both resprouts and seedlings varied from site to site in the proportion of resprouts:seedlings. Between 83–100% of the post‐fire populations of Cercocarpus betuloides, Arctostaphylos glandulosa, and Xylococcus bicolor were resprouts whereas 12–13% of Ceanothus tomentosus were resprouts. For Adenostoma fasciculatum, resprouts constituted 27–54% of the population at the lowest elevation and 65–94% at the highest elevation; whereas, the Quercus dumosa population was 100% resprouts at the lowest elevation and 31–67% resprouts at the highest elevation. Data are presented on the height of resprouts and seedlings for all species at the end of the first post‐fire year.
ULTRASTRUCTURE OF CEPHALEUROS VIRESCENS (CHROOLEPIDACEAE; CHLOROPHYTA). III. ZOOSPORES
Authors: Chapman Russell L.
Published: January 2018

Transmission electron microscopic examination ofCephaleuros virescensKunze growing on leaves ofCamelliaspp. andMagnolia grandifloraL. indicates that unreleased zoospores in mature zoosporangia are similar to those produced by the related genusPhycopeltis epiphytonMillardet and unlike the quadriflagellate motile cells produced by taxa in other families of Chlorophyta. The zoospores bear four smooth isokont bilaterally “keeled” flagella containing typical “9 + 2” axonemes and lacking scales. Flagellar insertion is apical and the parallel basal bodies overlap laterally at two levels. A cross section through the four basal bodies shows a trapezoidal arrangement wherein the two upper (anterior) basal bodies are closer together than are the lower (posterior) two. Serial sections indicate that diagonally opposing upper and lower basal bodies anchor flagella which emerge from the same side of the apical papilla. Each of the four basal bodies is associated with a microtubular spline which extends beneath the plasmalemma to the posterior end of the zoospore. A distinct multilayered structure is associated with each of the lower basal bodies. A nucleus, mitochondria (two of which are closely associated with the nucleus and spline microtubules), a chloroplast, and cytoplasmic haematochrome droplets are present in each zoospore. Pyrenoids and eyespots are absent. Flagellar insertion is characterized by “reversed bilateral symmetry”; and zoospores with both right‐handed and left‐handed arrangements are produced. The ultrastructure of the zoospores clearly indicates that: 1) the mode of flagellar insertion: 2) morphology, number, and arrangement of multilayered structures, and 3) bilaterally keeled flagella are characteristic of the Chroolepidaceae.
ROOT DIMORPHISM IN LUDWIGIA PEPLOIDES (ONAGRACEAE): STRUCTURE AND GAS CONTENT OF MATURE ROOTS
Authors: Ellmore George S.
Published: January 2018

Two distinct root types are borne on submerged nodes of the non‐woody amphibious plant, Ludwigia peploides (HBK) Raven. The anatomy of downward‐growing roots (DGR) and the negatively geotropic upward‐growing roots (UGR) demonstrates that structural elements shared by roots can be altered to produce highly modified organs differing in morphology, growth orientation, and in function. Both root types emerge contemporaneously from nodes and both have a similar pattern of cell lineages at the pole of the procambial cylinder. Differences between tissues of both roots become conspicuous with increasing distance from the root‐cap junction. In the distal cap of UGR, cells are spherical with much space between them unlike the more familiar tightly packed elements of DGR caps. In DGR, an uninterrupted epidermis surrounds the compact cortex and the hexarch stele occupies 25% of the root diameter. During primary growth, the DGR axis remains thin. In UGR, an open meshwork of cells covers the entire root surface, including the cap. The small stele has three or four xylem poles and fills only 5% of the UGR diameter. The unbranched axes of UGR swell and become spongy as strutlike arms radiate from cells of the primary cortex. Gas‐filled space between the arms comprises 88% of the axis volume in mature UGR. Although connections between shoot lacunae and spaces in UGR cannot be seen in the light microscope, gas can pass (25 ml/h) between nodes submerged in anaerobic substrate (O2 = 0.15 ppm) and UGR which reach the water surface. The porous axis of UGR thus provides a conduit for atmospheric gases into nodes which in turn produce the roots, vegetative branches, and reproductive shoots of this species.
COMPUTER SIMULATION OF BRANCH INTERACTION AND REGULATION BY UNEQUAL FLOW RATES IN BOTANICAL TREES
Authors: Honda Hisao , Tomlinson P. B. , Fisher Jack B.
Published: January 2018

Two aspects of branch interaction in trees are investigated theoretically. In the first it is assumed that there is a controlling factor in which the proximity of neighboring terminal branch units influences their branching capability. The almost horizontal tiers of lateral branches of Terminalia catappa L. and Cornus alternifolia L. are simulated by computer using values based on the measured branch geometries of real trees. For branch interaction, we assume a horizontal circle of inhibition whose center is the existing terminal point of a branch. If the end point of another branch extends into the circle, the original branch fails to bifurcate. Examples of computer simulated patterns are illustrated using different degrees of interference and are compared with branch tiers in T. catappa. In the second model the ability of a terminal branch unit to bifurcate is considered to be determined by the accumulation of a critical amount of a hypothetical growth‐ or bifurcation‐determining factor. The daughter branches of a bifurcation are assumed to have differing “flow rates,” i.e., the factor is distributed in different amounts between different daughter axes. Some simulated patterns generated by this model are very similar to real patterns found in T. catappa and an unnamed species of Tabernaemontana. In both simulations bifurcation ratios are determined and are shown to be a variable, not a fixed, property of the simulated trees.
CHANGES IN STARCH DISTRIBUTION IN THE OVERWINTERING ORGANS OF TYPHA LATIFOLIA (TYPHACEAE)
Authors: Kausch Albert P. , Seago James L. , Marsh Leland C.
Published: January 2018

Histochemical determinations for storage of carbohydrates in rhizomes, roots, and young shoots of Typha latifolia L. (Typhaceae) were conducted during the overwintering period from November to April. Early winter analysis showed that rhizomes and roots contained large amounts of starch (45.03% and 22.80% dry weight, respectively). The major storage tissue was parenchyma of the rhizome central core. From winter into spring a gradual decrease in storage starch in the rhizome and root occurred concurrently with starch accumulation near zones of rapid development in young shoots (buds), but the rhizome retained much starch (27.40% dry weight) into the start of its 2nd yr.
INVESTIGATIONS OF ANGIOSPERMS FROM THE MIDDLE EOCENE OF NORTH AMERICA: FLOWERS OF THE CELTIDOIDEAE
Authors: Zavada Michael S. , Crepet William L.
Published: January 2018

Flowers from the Middle Eocene Claiborne Formation of western Tennessee have both floral and palynological features suggestive of affinities with the subfamily Celtidoideae of the Ul‐maceae. Floral size, pollen size, and exine structure suggest that these flowers are intermediate between insect‐pollinated ancestors and the modern wind‐pollinated Celtidoideae. Thus, they represent the first direct fossil evidence supporting the widespread notion that at least some of the Amentiferae have been derived from insect‐pollinated ancestors.
EFFECTS OF ULTRAVIOLET‐B IRRADIANCES ON SOYBEAN. IV. LEAF ONTOGENY AS A FACTOR IN EVALUATING ULTRAVIOLET‐B IRRADIANCE EFFECTS ON NET PHOTOSYNTHESIS
Authors: Teramura Alan H. , Caldwell Martyn M.
Published: January 2018

There has recently been concern that some anthropogenic atmospheric pollutants, such as chlorofluoromethanes, may result in a global reduction in stratospheric ozone. This would undoubtedly increase the level of ultraviolet radiation reaching the surface of the earth. Such an increase in solar ultraviolet irradiation might have important biological consequences.

Unifoliate leaves of decapitated soybean plants were exposed to 0, 20, 50, and 90 effective mW m2 UV‐BBE (weighted ultraviolet‐B irradiance) from special lamps in a greenhouse. The effects of UV‐B radiation were examined in leaves at three different ontogenetic stages: bud; one‐third expanded, and fully expanded leaves. Leaf area expansion, net photosynthesis, specific leaf weight, chlorophyll concentrations, and acidified methanol extract absorbance were measured during the course of the study. These data revealed several generalizations concerning the relationship between leaf ontogeny and photosynthetic response to UV‐B radiation: 1) The rate and duration of leaf expansion are affected by low levels of UV‐B irradiation. 2) There appears to be a shift in the ontogenetic sequence of photosynthetic capacity as a function of leaf age. 3) This results in leaves of similar chronological ages being in different physiological stages of maturity.
NECTAR PRODUCTION, COMPOSITION, ENERGETICS AND POLLINATOR ATTRACTIVENESS IN SPRING FLOWERS OF WESTERN NEW YORK
Authors: Southwick Edward E. , Loper Gerald M. , Sadwick Steven E.
Published: January 2018

High Performance Liquid Chromatography (HPLC) was used to determine specific sugar ratios (fructose, glucose and sucrose) in nectars of nine families of flowering plants. All nectars contained all three sugars with the exception of that of Asclepias. Asclepias nectar was nearly a pure sucrose solution. Sucrose/hexose ratio was correlated with flower morphology, with tubular flowers having more sucrose and open flowers having more hexose. Open flowers contained nectar whose concentration was more affected by relative humidity than tubular flowers. Available nectar in unbagged flowers was found in volumes of 0.1 to 5 μl (17.5 to 68.2% sugar). Total sugar available per blossom amounted to 0.07 to 3.54 mg. We note that care must be taken in converting % concentration to mg sugar. Energetic yield was not as variable as the other measures and ranged from 0.72 to 3.58 cal/μl. Total daily nectar production was measured in five families and 24‐hr sugar production varied from 0.64 to 5.52 mg per flower. Insect nectar feeders frequently searched many blossoms with little or no reward, but were rewarded sufficiently at rare “lucky hit” blossoms which contained relatively large nectar rewards. Insect pollinators did not seek nectars of specific sucrose‐hexose ratios, but instead took nectar where caloric reward and accessibility made it most profitable.
DEVELOPMENT OF THE STIGMATIC SURFACE OF PRUNUS AVIUM L., SWEET CHERRY
Authors: Uwate W. J. , Lin J.
Published: January 2018

The stigmatic papillae of sweet cherry were examined to determine developmental characteristics of the wet‐stigma surface. Early stages of secretion are detectable 1 wk prior to anthesis by using a 1% crystal violet solution. The number of stainable cells and the amount of interstitial staining subsequently increase, although secretions are not visible on unstained specimens until anthesis. Auto‐fluorescence above 500 nm (excited by 335–480 nm) becomes microscopically detectable at floral maturity and grows more intense after anther dehiscence. Light microscopy of plastic sections shows that papillae degenerate in peripheral regions of unpollinated mature stigmas, and that this is even more pronounced in pollinated ones. The distal portions of the papillae are covered with a homogeneous cuticular cap, which when viewed with electron microscopy encloses a subcutaneous secretion prior to cuticle exfoliation. Other exudates observed with electron microscopy prior to anthesis are interstitial electron‐translucent globules and surrounding matrix, and assorted vesicles, lipid globules, and starch grains which are present at floral maturity. Flowers observed under field conditions in the terminal secretion stage accumulate trichomatous structures. Our observations indicate that the stigma of Prunus avium L. is characterized by several phases of secretion which appear to be facilitated by mechanical abrasion. A model for the primary pollen‐receptive area is proposed and suggestions are made concerning the origin of the secretions.
PALAEOSTACHYA DIRCEI N. SP., AN AUTHIGENICALLY CEMENTED EQUISETALEAN STROBILUS FROM THE MIDDLE PENNSYLVANIAN OF SOUTHERN ILLINOIS
Authors: Gastaldo Robert A.
Published: January 2018

Palaeostachya dircei n. sp. is described from an authigenically cemented specimen collected from the Anna Shale Member occurring above the Herrin (No. 6) Coal Member and below the Brereton Limestone in the Carbondale Formation, Kewanee Group (Middle Pennsylvanian). The strobilus is three‐dimensionally disposed within the matrix, allowing the preparation of ground thin sections, as well as selected maceration of the specimen. The imbricate strobilus is preserved for at least 7 cm of its original length and is composed of alternating whorls of sterile bracts and fertile sporangiophores. An articulated axis extends the length of the strobilus and attains a maximum width of 3 mm at the nodal areas. A whorl of 24 sterile bracts arises at each node, with each bract emerging at a 90° angle from the axis. Bracts are free except for a slight adaxial fusion at their point of origin. A slight downward‐projecting keel develops at the point where the bract begins ascending at least past the second supra‐adjacent node, where it is appressed into an abaxial furrow of the superposed bract. A whorl of sporangiophores originates above the bracts and is equal in number to the bracts. The sporangiophores are obliquely inserted on the axis and possess four superposed and thin‐walled sporangia inserted upon a (?) cruciate head. Spores assigned to Calamospora have been recovered and range in diameter from 68–115 μm (x̄ = 89 μm). The cone appears to be homosporous. Palaeostachya dircei n. sp. is compared to the reported permineralized and coalified compression species and appears similar to P. vera Seward and P. gracilis Renault.