Library

feed icon rss

Your email was sent successfully. Check your inbox.

An error occurred while sending the email. Please try again.

Proceed reservation?

Export
  • 1
    ISSN: 1365-3180
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary The emergence behaviour of weed species in relation to cultural and meteorological events was studied. Dissimilarities between populations in dormancy and germination ecology, between-year maturation conditions and seed quality and burial site climate all contribute to potentially unpredictable variability. Therefore, a weed emergence data set was produced for weed seeds of Stellaria media and Chenopodium album matured and collected from three populations (Italy, Sweden and UK). The seeds were collected in two consecutive seasons (1999 and 2000) and subsequently buried in the autumn of the same year of maturation in eight contrasting climatic locations throughout Europe and the USA. The experiment sought to explore and explain differences between the three populations in their emergence behaviour. Evidence was demonstrated of synchrony in the timing of the emergence of different populations of a species at a given burial site. The relative magnitudes of emergence from the three populations at a given burial site in a given year were generally similar across all the burial sites in the study. The resulting data set was also used to construct a simple weed emergence model, which was tested for its application to the range of different burial environments and populations. The study demonstrated the possibility of using a simple thermal time-based model to describe part of the emergence behaviour across different burial sites, seed populations and seasons, and a simple winter chilling relationship to adjust for the magnitude of the flush of emergence at a given burial site. This study demonstrates the possibility of developing robust generic models for simple predictions of emergence timing across populations.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 2
    Electronic Resource
    Electronic Resource
    Springer
    Naturwissenschaften 87 (2000), S. 398-403 
    ISSN: 1432-1904
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Natural Sciences in General
    Notes: Abstract  Fruits of Garden Lettuce, imbibed in 0.01 M KNO3, were depleted of maternal active phytochrome B by saturating deep-red exposure and photosensitized by chilling for 1 week at 4  °C. Twenty saturated fluence-response curves for photoinduced germination were elaborated between 300 and 800 nm, using exposure periods from 6 to 600 s at 22.5  °C; there is linear and closely parallel regression in the logarithmic probability net. The reciprocals of the half-response fluences obtained gave the apparent conversion spectrum of the controlling pigments and this was corrected for the transmittance of the seed-coat. It is a phytochrome spectrum of P r with photoconversion cross-sections of 1.2·109 and 4.5·103 m2 mol–1 at 666 and 800 nm, respectively. This means that for half-saturated germination of sensitized seed, fewer than 1 out of 200,000 phytochrome A molecules have to be photoconverted to P fr, and no photo-reversibility by deep-red was found. Therefore, all spectral colours of nightly moon- or skylight should stimulate the germination of sensitized weed seeds if they are exposed at the soil surface between sequential tillage operations.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 3
    Electronic Resource
    Electronic Resource
    Springer
    Naturwissenschaften 52 (1965), S. 209-209 
    ISSN: 1432-1904
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Natural Sciences in General
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 4
    ISSN: 1432-2048
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 5
    Electronic Resource
    Electronic Resource
    Springer
    Planta 64 (1965), S. 363-375 
    ISSN: 1432-2048
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Description / Table of Contents: Zusammenfassung Es wird über einige Beobachtungen berichtet, die für das Verständnis des Mechanismus der polarotropischen und phototropischen Krümmung bei schlauchförmigen Zellen mit Spitzenwachstum wesentlich sind. — Die positiv phototropischen Chloronemen sowohl vonStruthiopteris filicastrum All. als auch vonDryopteris filix-mas (L.)Schott wachsen im linear polarisierten Hellrot senkrecht zur Schwingungsebene (Abb. 2). Die Rhizoide vonDryopteris reagieren negativ phototropisch, und demgemäß entwickeln sie sich parallel zur Schwingungsebene. Bei den Rhizoiden vonStruthiopteris dagegen dominiert die positiv geotropische Reaktion. — Wird die Schwingungsebene um 90° gedreht, so ändert sich die Wachstumsrichtung der Chloronemen entsprechend (Abb. 3, oben). Ein bemerkenswerter Prozentsatz der Chloronemen reagiert jedoch abweichend. Es kommen einzellige Chloronemen vor, die Apikalkrümmung zeigen und zusätzlich einen neuen Wachstumspol im subapikalen Bereich bilden (Abb. 3, unten; Abb. 4). Bei anderen entsteht keine Apikalkrümmung, sondern es bilden sich ein oder zwei neue Wachstumszentren im subapikalen Bereich der Chloronemen (Abb. 4; Abb. 5f). Der Prozentsatz dieser abnorm reagierenden mehrpoligen Chloronemen erhöht sich, wenn gleichzeitig mit der Drehung der Schwingungsebene die Intensität heraufgesetzt wird. Eine Drehung der Schwingungsebene um 90° scheint außerdem eine kurzzeitig erniedrigte Wachstumsleistung zur Folge zu haben. Wenn man die Vorstellung zugrunde legt (Jaffe andEtzold 1962,Etzold 1965), daß die im Apex vorkommenden hellrot absorbierenden dichroitischen Photoreceptoren oberflächenparallel in der wandständigen Cytoplasmaschicht gelagert sind (Abb. 6), so müssen unsere Befunde auf der Basis interpretiert werden, daß den Zonen stärksten Wachstums die Zonen stärkster Strahlungsabsorption entsprechen. Das Entstehen neuer Wachstumszentren im subapikalen Bereich der Chloronemen zeigt, daß an der Basis der halbkugeligen Chloronemaspitzen und sogar weiter basalwärtz zwar reduzierte, aber noch nachweisbare Hellrotempfindlichkeit und Wachstumsfähigkeit bestehen. Die polarotropische und phototropische Krümmung der Keimschläuche muß daher — analog den Befunden beiPilobulus-Sporangiophoren (Page 1962) — so aufgefaßt werden, daß an den Orten der stärksten Lichtabsorption jeweils neue Wachstumszentren entstehen. Dieser Mechanismus der phototropischen Krümmung ist grundsätzlich verschieden von dem, der von Sproßachsen oder Koleoptilen her bekannt ist.
    Notes: Summary We report some observations which seem to be important for an understanding of the mechanism of the polarotropic and phototropic response of filamentous cells with tip growth. — The chloronemata, i. e. the filamentous young gametophytes of the fernStruthiopteris filicastrum All. show nearly the same polarotropic behaviour as the corresponding filaments of the fernDryopteris filix-mas (L.)Schott. In linearly polarized red light the positive phototropic chloronemata grow perpendicular to the plane of vibration (Fig. 2). — The rhizoids behave differently. In the case ofDryopteris they show negative phototropic reaction and therefore grow parallel to the plane of vibration whereas inStruthiopteris the rhizoids will grow downwards into the agar. This fact indicates a positive geotropic reaction. If the plane of vibration is turned by 90° the direction of growth of the chloronemata will change correspondingly (Fig. 3, above). A remarkable percentage of the chloronemata, however, reacts differently. There are unicellular chloronemata which show a curvature of the tip and additionally a new filament below the apex (Fig. 3; Fig. 4). Other types show no curvature of the tip at all but one or two new filaments originate at some distance below the apex, i. e. in the “subapical region” of the chloronema (Fig. 4; Fig. 5, f). The occurence of these phenomena is augmented if the intensity of the polarized red light is increased at the moment when the plane of vibration is turned. There is also some evidence that a turning of the plane of vibration by 90° leads to a transient reduced activity of growth. If we make the reasonable assumption (cf.Jaffe andEtzold 1962,Etzold 1965) that the dichroic red-absorbing photoreceptors occuring in the apex are oriented parallel to the nearby surface of the cell (Fig. 6), our observations must be interpreted under the point of view that the region of the highest activity of growth within the chloronema is determined by the zone of highest absorption of red light. If the plane of vibration is perpendicular to the longitudinal axis of the chloronema, growth is necessaryly confined to the extreme tip of the apex. If, however, the plane of vibration is parallel to the longitudinal axis the highest absorption in the apical region will take place on the flanks of the apex. Therefore the area of the highest growth activity is shifted to one or the other flank of the apex. The result is a polarotropic curvature. — Our additional observations, the formation of new centers of growth in the subapical region of the chloronema, indicate the existence of some red light sensitivity and growth potentiality also in the subapical region where normally the activity of growth had ceased. These findings support the view that the polarotropic and phototropic curvatures of the chloronema come about because new centers of growth originate in the zones of highest light absorption. Similar conclusions were reached byPage (1962) who studied the phototropic response of sporangiophores ofPilobolus. — This particular mechanism of phototropic response is fundamentally different from the mechanism of the phototropic response of stems or coleoptiles.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 6
    Electronic Resource
    Electronic Resource
    Springer
    Planta 79 (1968), S. 271-274 
    ISSN: 1432-2048
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary An action spectrum for photoinduced sporulation (conidia formation) in Trichoderma viride is presented. The detectable quantum efficiency was between 350 and 550 nm with peaks near 380 and 440 nm with a minimum at about 400 nm. Essentially no sporulation occurred at 254 nm or from 525 to 1100 nm. The half maximum response is reached with 6.6·10-10 Einstein/cm2 at 447 nm.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 7
    Electronic Resource
    Electronic Resource
    Springer
    The European physical journal 282 (1977), S. 293-301 
    ISSN: 1434-601X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Forα-nucleus potentials which contain a pocket, the scattering matrix may be split into ‘barrier’ and ‘internal’ components. Using simple parametrizations for these components, analytic expressions are derived for the corresponding ‘barrier’ and ‘internal’ cross sections. The oscillations present in these cross sections are interpreted as arising from interference between various terms in the Poisson summation formula for the scattering amplitudes. At backward angles the ‘internal’ cross section and the cross sections resulting from various Regge pole models are shown to have the same angular dependence. A method is given to locate roughly the position of the dominant Regge pole of the scattering matrix. At more foreward angles the ‘internal’ cross section, unlike those from the Regge pole models, describes the nuclear refraction undergone byα-particles that are transmitted through the target. Such refraction effects have previously been invoked to explain intermediate energyα-nucleus scattering.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 8
    Electronic Resource
    Electronic Resource
    Springer
    Planta 86 (1969), S. 235-249 
    ISSN: 1432-2048
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The induction of flowering in mustard (Sinapis alba L.) was studied by means of night-breaks (“Störlicht”). The plants were cultivated under fully controlled conditions: 8000 Lux white light (mixed fluorescent and incandescent) 18°C, 80% relative humidity. Raised under our conditions in short days (8 hours of white light) mustard behaved as a quantitative long-day plant (Fig. 2). Flowering can be promoted by long-day treatment (Fig. 3). The long day (16 hours of white light) can be replaced by a short day plus a night-break. The highest effectiveness of the night-break is found near the middle of the dark period (Figs. 4, 5). —The spectral dependence of flower induction was studied with blue, green, yellow, red (Fig. 1) and far-red light using a 2-hour break near the middle of the dark period. The dose response curves (Fig. 6) and the action spectrum (Fig. 7) indicate a very strong effectiveness in the blue part of the spectrum, a small response in red and yellow light and no response at all in green and far-red light. The participation of phytochrome is indicated (Table 1), but no far-red reversibility could be detected (Table 2). Simultaneous irradiation with red and far-red light yielded significant enhancement effects (Fig. 8). In view of the strong shadowing in the leaves (Figs. 9, 10) these data are interpretable on the basis of phytochrome.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 9
    ISSN: 1434-601X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract An additive two-component model (direct plus thermal) is used together with an empirical power law for composite particle production to calculate inclusive cross sections for light fragment emission. The ratio of neutron to proton inclusive production is also studied. We compare our results with recent experimental data.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 10
    Electronic Resource
    Electronic Resource
    Springer
    The European physical journal 311 (1983), S. 131-133 
    ISSN: 1434-601X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract In reactions between very asymmetric projectile-target systems charge is preferably transferred from the lighter to the heavier nucleus. This leads to a decrease of the potential barrier between the nuclei and increase of the fusion cross-section. We perform trajectory calculations with energy dissipation and proton transfer to estimate the magnitude of the effect.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
Close ⊗
This website uses cookies and the analysis tool Matomo. More information can be found here...