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  • 1
    Electronic Resource
    Electronic Resource
    Correlation of molecular hydrogen dissociation and the film quality of diamondlike carbon in plasma enhanced chemical vapor deposition (1995)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 66 (1995), S. 3152-3154 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The ground state atomic hydrogen density in a hydrogen/acetylene discharge is compared with the diamondlike carbon (DLC) film quality as determined from in situ ellipsometry measurement of the refractive index. Two-photon laser-induced fluorescence (LIF) was employed for the detection of the ground state atomic hydrogen in the rf generated discharge. Absolute atomic hydrogen number densities were determined by calibrating the LIF detection system using a transfer standard. A direct correlation was found between the level of molecular hydrogen dissociation in the plasma and the refractive index of the DLC film. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.113706
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  • 2
    Electronic Resource
    Electronic Resource
    South and East African Stone Age Typology (1935)
    [s.l.] : Nature Publishing Group
    Nature 136 (1935), S. 760-761 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] IN my letter in NATURE of September 21, p. 475, in the fifth paragraph, I said that the oscillation which marks Bed III at Oldoway and the Intrapluvial in Pluvial II, in Uganda, “may be equated with that between the Kamasian and Gamblian” of Kenya. That was wrong, for it has recently become ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/136760c0
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  • 3
    Electronic Resource
    Electronic Resource
    South and East African Stone Age Typology (1935)
    [s.l.] : Nature Publishing Group
    Nature 136 (1935), S. 475-475 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] Two separate communications1,2 this year on the archæology of South Africa bear indirectly on East African problems now being investigated in Uganda by this expedition. In the first, Prof. Dreyer directs attention to the similarity that exists, in his opinion, between ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/136475a0
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  • 4
    Electronic Resource
    Electronic Resource
    South and East Africa Stone Age Typology (1936)
    [s.l.] : Nature Publishing Group
    Nature 137 (1936), S. 236-237 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] IN his recent letter1, Prof. Dreyer remarks that discoveries in East Africa may perhaps throw light on, and be interpreted with due regard to, problems in South Africa. For similar reasons the investigations in South Africa arouse like hopes among archæologists elsewhere. ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/137236b0
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  • 5
    Electronic Resource
    Electronic Resource
    Pit-field distribution, plasmodesmatal frequency, and assimilate flux in the mestome sheath cells of wheat leaves (1974)
    Springer
    Planta 121 (1974), S. 97-118 
    Details
    ISSN: 1432-2048
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The distribution of pit fields and plasmodesmata in the mestome-sheath cells of a wheat leaf has been determined by study of sections and partial macerates. Each bundle is approximately symmetrical about the sagittal plane and most plasmodesmata occur in the mestome sheath where its cells abut the metaphloem. Plasmodesmata are absent adjacent to xylem vessels, and the frequency of plasmodesmata declines sharply in cells that lie close to the sagittal plane. Calculations show that 1 cm2 of leaf lamina has approximately 2x108 plasmodesmatal connections to the phloem of the longitudinal veins, and that 85% of these connections are to the late-maturing intermediate bundles that do not complete their differentiation until leaf growth is nearly finished. The phloem area of inner tangential wall of the mestome sheath amounts to 0.26 cm2 per cm2 of leaf area and plasmodesmata occupy 1.5% of this area. These anatomical facts are used to estimate the sugar flux across the inner-tangential wall of the sheath as 2x102 pmol s-1 cm2 sheath. Further analysis strongly suggests that this flux must cross the sheath by diffusion through the plasmodesmata, creating there a flux of 1.5x104 pmol s-1 cm-2 plasmodesma. These results are compared with data recently obtained for the transfer-cell/sieve-element boundary in Vicia and are found to be about one tenth of the flux in that system, the transfer being adequately driven by a concentration gradient of 50 μg cm-3 of sugar across the sheath. Such a concentration gradient could be achieved by the photosynthetic activity of about 50 chloroplasts acting for about 2 min. The transverse veins that lack a mestome sheath are unlikely to account for more than 10% of the fluxes calculated here and have been ignored in the calculations. It is concluded that the symplastic pathway is the only possible one for assimilate traffic across the mestome sheath in wheat, and that diffusion down a gradient of sugar concentration from the chloroplasts to the sheath acts as the driving force. This suggestion is reinforced by analysis of the contributions of the larger and smaller veins to the water flux from the same square centimetre of leaf. This analysis shows that 99% of the water flux must exit from the xylem of the 7 large bundles, presumably through the apoplast, securing an effective separation between the inwardly directed flow of sugar (laoded symplastically chiefly through the small longitudinal bundles) and the outwardly directed, very much larger flux of water.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00388750
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  • 6
    Electronic Resource
    Electronic Resource
    Lignified sieve elements in the wheat leaf (1974)
    Springer
    Planta 117 (1974), S. 349-353 
    Details
    ISSN: 1432-2048
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Sieve elements with thick, lignified walls are identified in the longitudinal bundles of the wheat leaf and appear to be functional. They are also present in several festucoid grasses but appear to be absent from the panicoid grasses examined.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00388029
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  • 7
    Electronic Resource
    Electronic Resource
    Changes in actin organization in the living egg apparatus of Torenia fournieri during fertilization (2000)
    Springer
    Sexual plant reproduction 12 (2000), S. 315-322 
    Details
    ISSN: 1432-2145
    Keywords: Key words Actin ; Egg apparatus ; Fertilization ; Microinjection ; Torenia fournieri
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract  Changes in actin organization in the living egg apparatus of Torenia fournieri from anthesis to post-fertilization have been investigated using microinjection and confocal microscopy. Our results revealed that the actin cytoskeleton displays dramatic changes in the egg apparatus and appears to coordinate the events of synergid degeneration, pollen tube arrival and gametic fusion during fertilization. Synergid degeneration occurs after anthesis and is accompanied by actin fragmentation and degradation. The actin cytoskeleton becomes organized with numerous aggregates in the chalazal end of the degenerating synergid, and some of the actin infiltrates into the intercellular gap between synergids, egg and central cell, forming a distinct actin band. An actin cap is present near the filiform apparatus after anthesis and disappears after pollen tube arrival. In the egg cell, actin filaments initially organize into a network and after pollination become fragmented into numerous patches in the cortex. These structures, along with the actin in the degenerating synergid and intercellular spaces form two distinct actin coronas during fertilization. The actin coronas vanish after gametic fusion. This is the first report of changes in actin organization in the living egg apparatus. The reorganization of the actin cytoskeleton in the egg apparatus and the presence of the actin coronas during fertilization suggest these events may be a necessary prelude to reception of the pollen tube and fusion of the male and female gametes.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004970000026
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  • 8
    Electronic Resource
    Electronic Resource
    Histochemistry and fine structure of developing wheat aleurone cells (1975)
    Springer
    Planta 123 (1975), S. 105-116 
    Details
    ISSN: 1432-2048
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Developing aleurone cells can first be distinguished 10 days after anthesis beneath the degenerating nucellus as somewhat cuboidal cells with extremely thin walls and large nuclei. Ribosomes are very abundant but little endoplasmic reticulum (ER) is apparent. By 14 days the cell walls are intensely autofluorescent, possibly due to the presence of a ferulic acid-carbohydrate complex. At this stage the cytoplasm is characterized by the presence of large vacuoles, many of which contain small, electron-dense inclusions, presumably the beginnings of the phytin globoids (Type I inclusions) of mature aleurone grains. The paired appearance of many of the cells suggests that they are dividing periclinally, the innermost cells destined to become part of the starchy endosperm. By 4 weeks the cell walls have greatly thickened, ER and mitochondria have proliferated, and the vacuoles, which subsequently give rise to mature aleurone grains, contain a second type of inclusion (Type II inclusion) embedded in a protein matrix. Although the walls remain uniformly autofluorescent, an intensely stained inner wall can be distinguished readily from the outer wall. By 5 weeks the aleurone grains are almost completely surrounded by lipid droplets and contain numerous Type I inclusions. The cells change little in appearance from 6 weeks to maturity. At the latter stage the inner and outer walls are quite distinct and the cytoplasm is densely packed with aleurone grains which are completely surrounded by lipid droplets and interspersed with occasional plastids and numerous mitochondria with rather indistinct cristae.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00383859
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  • 9
    Electronic Resource
    Electronic Resource
    Initital cellularization and differentiation of the aleurone cells in the ventral region of the developing wheat grain (1978)
    Springer
    Planta 140 (1978), S. 19-30 
    Details
    ISSN: 1432-2048
    Keywords: Aleurone ; Endosperm ; Triticum
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Early cellularization of the free-nuclear endosperm and subsequent differentation of the aleurone cells in the ventral region of the developing wheatgrain (Triticumaestivum L. cv. Heron) were examined using both light and electron microscopy. In ovules harvested 1 d after anthesis, irregular wall ingroths typical of transfer cells protrude into the multinucleate cytoplasm. Initital cellularization occurs by a process of free wall formation in much the same fashion as in the dorsal region of the grain. In places, sheets of endoplasmic reticulum and dictyosomes appear to be closely associated with the growing wall. Like the wall ingrowths noted earlier, the freely growing walls are intensely fluorescent after staining with aniline blue. Initiatal cellularization is complete 2–3 days after anthesis. Unlike the first-formed cells in the dorsal region of the developing grain, those in the ventral region are not meristematic. These amitotic cells become the groove aleurone cells which at an early stage of development are set apart from the rest of the endosperm by their irregularly thickened walls and dense cytoplasm. Autofluorescence is first apparent in the walls of those cells next to the degenerating nucellus. In contrast to the aleurone cells in the dorsal region of the grain, at maturity only the inner wall layer of each of the groove aleurone cells remains autofluorescent. The aleurone grains are highly variable in appearance and contain no Type II inclusions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00389375
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  • 10
    Electronic Resource
    Electronic Resource
    Penetration of Phytophthora cinnamomi into disease tolerant and susceptible eucalypts (1976)
    Springer
    Archives of microbiology 108 (1976), S. 231-242 
    Details
    ISSN: 1432-072X
    Keywords: Phytophthora ; Penetration ; Eucalypts ; Roots ; Electron microscopy ; Appressoria ; Plugs
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The mechanisms of penetration of Phytophthora cinnamomi Rands into seedling eucalypt roots were studied by light and electron microscopy. Culture grown seedlings of root-rot tolerant Eucalyptus st johnii and root-rot susceptible Eucalyptus obliqua were inoculated with both zoospores and mycelium. Zoospores encysted on roots of both species and the germ tubes penetrated without the formation of appressoria. Swellings, previously described as appressoria, were formed when the germ tube was slow to enter the host by intracellular penetration. Vegetative hyphae penetrated both inter- and intracellularly into the zones of root elongation and differentiation, often through root hairs. Evidence of hydrolysis of the host cell-wall at the point of penetration was observed in electron micrographs. Several hours after the germ tube penetrated the epidermis, a thick plug of amorphous material formed in the germ tube slightly below the level of the outer walls of the epidermal cells, sealing off the hypha within the root. Behaviour of zoospores and germ tubes and the mechanism of penetration were similar on both hosts. Micrographs do not suggest any kind of a hypersensitive reaction by the host cells during the early stages of infection.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00454847
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