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  • 1
    Electronic Resource
    Electronic Resource
    Microplankton population structure in Southern California nearshore waters in late spring (1980)
    Springer
    Marine biology 60 (1980), S. 209-226 
    Details
    ISSN: 1432-1793
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Taxonomic composition, biomass as organic carbon, numerical abundance, and size distribution of the microplankton were determined at 6 Southern California nearshore locations in late May–early June, 1970. Samples were taken at approximately 5 m (10 m at one station) intervals through the upper 40 to 50 m to reveal some of the small-scale differences and levels of variability in the populations. Total microplankton biomass over all euphotic zone samples varied by more than two orders of magnitude (7.6 to 1,200 μg C l-1). Average biomass at comparable sites (n=5) ranged from 48 to 240 μg C l-1; biomass range within stations varied from about 5-fold to 120-fold. Total microplankton numbers varied approximately 22-fold (4.3×105 to 9.5×106 organisms l-1) over all euphotic zone samples, but the range within stations was always less than an order of magnitude. At comparable stations, nanoplankton biomass had ranges extending from 3.7-fold to 12-fold; its average percentage contribution (±1 SD) to the total microplankton biomass varied from 39±5% to 54±13%. Netplankton biomass showed a similar minimal range, but its greatest range was more than two orders of magnitude. Ranges of abundance of major taxonomic groups within stations varied considerably from about 2-fold to more than three orders of magnitude. The small-scale variability of the populations probably affects the reliability of the microplankton as a food source for pelagic consumers.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00389164
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  • 2
    Electronic Resource
    Electronic Resource
    Micro-zooplankton and its abundance relative to the larger zooplankton and other seston components (1969)
    Springer
    Marine biology 4 (1969), S. 182-189 
    Details
    ISSN: 1432-1793
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Micro-zooplankton populations in the upper 100 m were sampled from 5 marine environments in the northeast Pacific Ocean extending from slope waters off San Diego to an oceanic site near Isla Guadalupe, and their abundance related to that of the larger zooplankton, phytoplankton (as estimated from chlorophyll a), and detritus. The micro-zooplankton and other components of the seston were subdivided into 3 fractions on the basis of size in the deck-mounted collecting unit of a seawater pumping system. Through the euphotic zone at each site, the Protozoa, of which ciliates were the dominant forms, accounted for 95% or more of the total micro-zooplankton numbers. Their biomass, as volume, was estimated to be 13 to 28% of that of the total micro-zooplankton. The standing stock of micro-zooplankton over the euphotic zone at the various sites, in terms of dry weight, was estimated to be 14 to 34% (average 23%) of that of the phytoplankton crop. Micro-zooplankton volumes in the upper 100 m were 21 to 26% of those for the larger zooplankton sampled over the same depth.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00393891
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  • 3
    Electronic Resource
    Electronic Resource
    Studies on the functional role of tintinnids in the Southern California Bight. III. Grazing impact of natural assemblages (1979)
    Springer
    Marine biology 52 (1979), S. 23-32 
    Details
    ISSN: 1432-1793
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Tintinnids were identified and enumerated in samples from 100 stations in the Southern California Bight. Spring and summer samples were collected at weekly intervals at 3 locations off La Jolla, California (USA) in 1967. Samples were also taken at considerably wider spatial and temporal intervals during 4 cruises in the fall and winter of 1974–1975. Ninety-one species of tintinnids were identified, comprising assemblages ranging in density to over 18x106 tintinnids m-3. Previously published accounts of the feeding rates and behavior of tintinnids were then applied to this tintinnid assemblage in order to estimate their impact on the flow of carbon through the planktonic food web. Generally, for both surveys, less than 4% of the daily primary production was consumed by the observed tintinnid stocks, although at 14 stations calculated ingestion by tintinnids exceeded 10% and at 4 stations it exceeded 20% of the measured daily primary production. Other ciliates in the 1967 samples were, combined, approximately as abundant as the tintinnids; if their grazing rates were comparable, the consumption by the total ciliate assemblage would be double that of the tintinnids alone. The high tintinnid growth efficiencies previously observed (Heinbokel, 1978a) and the relatively high efficiency with which tintinnids can be grazed by larger consumers suggest that relatively little of the energy and material fixed by the nanno-phytoplankton may be lost to the larger consumers by the insertion of a ciliate “extra link” into the food chain.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00386854
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  • 4
    Electronic Resource
    Electronic Resource
    Ultrastructure of and plasmodesmatal frequency in mature leaves of sugarcane (1991)
    Springer
    Planta 184 (1991), S. 291-306 
    Details
    ISSN: 1432-2048
    Keywords: C4 plant ; Leaf ultrastucture ; Mestome ; sheath ; Phloem loading ; Plasmodesma ; Saccharum (plasmodesmata) ; Vascular bundle
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Vascular bundles and contiguous tissues of leaf blades of sugarcane (Saccharum interspecific hybrid L62–96) were examined with light and transmission electron microscopes to determine their cellular composition and the frequency of plasmodesmata between the various cell combinations. The large vascular bundles typically are surrounded by two bundle sheaths, an outer chlorenchymatous bundle sheath and an inner mestome sheath. In addition to a chlorenchymatous bundle sheath, a partial mestome sheath borders the phloem of the intermediate vascular bundles, and at least some mestome-sheath cells border the phloem of the small vascular bundles. Both the walls of the chlorenchymatous bundlesheath cells and of the mestome-sheath cells possess suberin lamellae. The phloem of all small and intermediate vascular bundles contains both thick- and thin-walled sieve tubes. Only the thin-walled sieve tubes have companion cells, with which they are united symplastically by pore-plasmodesmata connections. Plasmodesmata are abundant at the Kranz mesophyll-cell-bundlesheath-cell interface associated with all sized bundles. Plasmodesmata are also abundant at the bundle-sheathcell-vascular-parenchyma-cell, vascular-parenchyma-cellvascular-parenchyma-cell, and mestome-sheath-cell-vascular-parenchyma-cell interfaces in small and intermediate bundles. The thin-walled sieve tubes and companion cells of the large vascular bundles are symplastically isolated from all other cell types of the leaf. The same condition is essentially present in the sieve-tube-companion-cell complexes of the small and intermediate vascular bundles. Although few plasmodesmata connect either the thin-walled sieve tubes or their companion cells to the mestome sheath of small and intermediate bundles, plasmodesmata are somewhat more numerous between the companion cells and vascular-parenchyma cells. The thick-walled sieve tubes are united with vascular-parenchyma cells by pore-plasmodesmata connections. The vascular-parenchyma cells, in turn, have numerous plasmodesmatal connections with the bundle-sheath cells.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00195330
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  • 5
    Electronic Resource
    Electronic Resource
    Fine structure of plasmodesmata in mature leaves of sugarcane (1991)
    Springer
    Planta 184 (1991), S. 307-318 
    Details
    ISSN: 1432-2048
    Keywords: C4 plant ; Intercellular communication ; Phloem ; Plasmodesma ; Saccharum (plasmodesmata) ; Vascular bundle ; Xylem
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The fine structure of plasmodesmata in vascular bundles and contiguous tissues of mature leaf blades of sugarcane (Saccharum interspecific hybrid L62–96) was studied with the transmission electron microscope. Tissues were fixed in glutaraldehyde, with and without the addition of tannic acid, and postfixed in OsO4. The results indicate that the fine structure of plasmodesmata in sugarcane differs among various cell combinations in a cell-specific manner, but that three basic structural variations can be recognized among plasmodesmata in the mature leaf: 1) Plasmodesmata between mesophyll cells. These plasmodesmata possess amorphous, electron-opaque structures, termed sphincters, that extend from plasma membrane to desmotubule near the orifices of the plasmodesmata. The cytoplasmic sleeve is filled by the sphincters where they occur; elsewhere it is open and entirely free of particulate or spokelike components. The desmotubule is tightly constricted and has no lumen within the sphincters, but between the sphincters it is a convoluted tubule with an open lumen. 2) Plasmodesmata that traverse the walls of chlorenchymatous bundle-sheath cells and mestome-sheath cells. In addition to the presence of sphincters, these plasmodesmata are modified by the presence of suberin lamellae in the walls. Although the plasmodesmata are quite narrow and the lumens of the desmotubules are constricted where they traverse the suberin lamellae, the cytoplasmic sleeves are still discernible and appear to contain substructural components there. 3) Plasmodesmata between parenchymatous cells of the vascular bundles. These plasmodesmata strongly resemble those found in the roots of Azolla, in that their desmotubules are closed for their entire length and their cytoplasmic sleeves appear to contain substructural components for their entire length. The structural variations exhibited by the plasmodesmata of the sugarcane leaf are compared with those proposed for a widely-adopted model of plasmodesmatal structure.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00195331
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  • 6
    Electronic Resource
    Electronic Resource
    Future Large-Scale Surveys of `Interesting' Stars in the Halo and Thick Disk of the Galaxy (1999)
    Springer
    Astrophysics and space science 265 (1999), S. 547-552 
    Details
    ISSN: 1572-946X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The age of slow, methodical, star-by-star, single-slit spectroscopic observations of rare stars in the halo and thick disk of the Milky Way has come to an end. The use of new spectroscopic survey techniques which obtain large sky coverage to faint magnitudes will enable substantially better `return on investment' in the near future. We review the present state of surveys for low metallicity, field horizontal-branch, and sdM stars in the Galaxy, and describe new lines of attack which should open the way to a more than hundredfold increase in the numbers of interesting stars with available spectroscopic information.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1002160111354
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  • 7
    Electronic Resource
    Electronic Resource
    Strömgren 4-Color Photometry of Very Metal-Poor Stars (1999)
    Springer
    Astrophysics and space science 265 (1999), S. 183-184 
    Details
    ISSN: 1572-946X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Strömgren uvby photometry has been observed for an additional 140 very metal-poor stars from the survey of Beers et al. (1992). These Galactic stars of very-low metallicity provide crucial information for the investigation of the formation and evolution of the Galaxy, as well as on the nature of the early Universe. The Strömgren uvby-β system allows the measurement of stellar atmospheric parameters as a prelude to detailed abundance studies which will make use of high-resolution spectroscopy and the new generation of large telescopes. The photometric techniques developed by Schuster et al. (1996) are used not only to classify these very metal-poor stars but also to derive effective temperatures, surface gravities, and improved estimates for their interstellar reddenings. In particular, photometric diagrams such as [c 1], [m 1] and c 0, (b-y)0 are used to classify these stars, especially those near the main-sequence turnoff, where contamination from slightly-evolved subgiants, lower surface-gravity horizontal-branch stars, and even a few supergiant or AGB candidates is found.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1002147123765
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  • 8
    Electronic Resource
    Electronic Resource
    The Metallicity Distribution Function of Extremely low-Metallicity Stars (1999)
    Springer
    Astrophysics and space science 265 (1999), S. 105-113 
    Details
    ISSN: 1572-946X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We discuss new results based on the many thousands of extremely metal-poor stars discovered in the ongoing HK survey of Beers and collaborators. The present status of the photometric and spectroscopy follow-up efforts are summarized, and the nature of the halo metallicity distribution function is considered. We point out the existence of apparent complexities in the kinematics of the lowest abundance stars in the Galaxy, and discuss the presence of a large fraction of carbon-enhanced stars among the HK survey stars with [Fe/H] ≤ −2.0.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1002110115587
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  • 9
    Electronic Resource
    Electronic Resource
    Abundances in Very Metal-Poor Stars (1999)
    Springer
    Astrophysics and space science 265 (1999), S. 141-144 
    Details
    ISSN: 1572-946X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1002170401475
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  • 10
    Electronic Resource
    Electronic Resource
    The Low Metallicity Tail of the Halo Metallicity Distribution Function (1998)
    Springer
    Space science reviews 84 (1998), S. 139-144 
    Details
    ISSN: 1572-9672
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Ongoing spectroscopy and photometry of stars selected in the HK objective-prism/interference-filter survey of Beers and colleagues has resulted in the identification of many hundreds of additional stars in the halo (and possibly the thick disk) of the Galaxy with abundances [Fe/H] ≤ -2.0. A new calibration of the technique for estimation of metal abundance based on a CaII K index as a function of broadband B - V color is applied to obtain metallicities for stars observed with the SSO 2.3m and INT 2.5m telescopes. This new data is combined with other samples of extremely metal-deficient stars (Ryan and Norris, 1991a; Beers et al., 1992; Carney et al., 1994) to form a large database of objects of low metallicity. The combined sample is examined and compared with expectations derived from a Simple Model of Galactic chemical evolution. There appears to be a statistically-significant deficit of stars more metal-weak than [Fe/H] = -3.0. An abundance of [Fe/H] ≈ -4.0 can be taken as the low-metallicity limit for presently-observable stars in the Galaxy.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1005054831184
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