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  • 1
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Plant, cell & environment 2 (1979), S. 0 
    ISSN: 1365-3040
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Abstract. The concentration of sugar in the nectars of unprotected flowers of several species was measured and did not reach the high values that would be in equilibrium with the daytime humidities recorded outside the corolla, although the sugar concentration was highly correlated with ambient relative humidity. This paper examines features that maintain low nectar sugar concentrations at low ambient humidities. Post-secretory changes in concentration are influenced to a small extent by nectar composition but depend largely on physico-chemical and microclimatic effects. Factors contributing to the maintenance of steep gradients in water activity between the nectar and the ambient air include corolla morphology, sugar concentration gradients and waterproofing lipid monolayers on the nectar surface. This paper considers the relative importance of such features in relation to the pollination syndrome. A simple technique is described for the measurement of intrafloral relative humidity.
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  • 2
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Plant, cell & environment 5 (1982), S. 0 
    ISSN: 1365-3040
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Abstract. The measurements of Yes'kov & Sapozhnikov (1976) suggest that electrostatic potentials on foraging honeybees can reach hundreds of volts. Pollen grains of oilseed rape, Brassica napus L., subjected experimentally to potentials of this order, jumped a distance that increased approximately as the square of the voltage, between two pin electrodes on which, in some experiments, were impaled an anther or stigma of oilseed rape or a freshly-killed honeybee. Most floral surfaces were insulated, but there was a low-impedance path to earth via the stigma, and the electrostatic field due to an approaching charged bee must therefore concentrate there. Thus, if electrostatic potentials of this magnitude occur in nature they may increase the chance that pollen from bees will reach the stigma rather than other floral surfaces, as well as enabling pollen to jump from anther to bee and from bee to stigma across an air gap of the order of 0.5 mm.
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    Oecologia 114 (1998), S. 349-360 
    ISSN: 1432-1939
    Keywords: Key words Resource limitation ;  Pollinator limitation  ;  Seed development  ;  Fruit development  ; Ovule position
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract This paper explores spatial and temporal patterns in the interaction of pollination and resources as constraints on the initiation and maturation of fruits and seeds in bluebell (Hyacinthoides non-scripta, Liliaceae). Field and laboratory experiments showed a degree of self-incompatibility (cross-pollination gave greater seed and fruit numbers than self-pollination), and pollinator limitation (hand cross-pollination gave greater seed and fruit numbers than open-pollination) as well as␣resource limitation. Bud removal, designed to relax interfruit competition for resources in the remaining flowers, increased percent fruit maturation in unpollinated flowers and increased the percent of initiated seeds that matured in cross-pollinated flowers. Clear position effects were also found. In an ovary, ovules near the stylar end showed a higher percent seed maturation than basal ovules. On a raceme, terminal flowers showed lower percent fruit initiation and maturation and lower seed numbers than basal flowers. The balance between resource limitation and pollinator limitation changed with position on the raceme. Temporal patterns involved raceme death and abortion of flowers, fruits or seeds. A lattice diagram schematises the hypothetical modulation by pollination of resource-dependent serial adjustment of maternal investment.
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  • 4
    Electronic Resource
    Electronic Resource
    [s.l.] : Nature Publishing Group
    Nature 182 (1958), S. 194-194 
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] In Fig. 1 the emergence curve of A. cyanea is compared with that of A. imperator, a spring species in the same family and of similar size. The two curves differ significantly in the degree of their synchronization, a point well demonstrated by comparing the times during which 50 per cent of the ...
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  • 5
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] Table 1 Mean Percentage of Immature Germ Cells in the Ejaculated Seminal Fluid of Human Males with Different Sperm Qualities Sperm quality No. of sperm No. of subjects Spermatogonia Spermatocytes Spermatids Total (million/ml.) investigated (%) (%) (%) (%) ...
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  • 6
    Electronic Resource
    Electronic Resource
    [s.l.] : Nature Publishing Group
    Nature 243 (1973), S. 537-538 
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] The experimental animals were kept at 25 C in a photo-periodic regime of 12 h light : 12 h dark, from the wandering stage of the last larval instar onwards. Males and females were kept in separate incubators. Each day at lights-off the moths that had emerged during the past 24 h were removed from ...
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  • 7
    ISSN: 1432-1939
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Wasps (Dolichovespula and Vespula spp.) worked predominantly upwards when foraging for nectar on inflorescences of the protogynous Scrophularia aquatica, in which the standing crop of nectar sugar per flower showed no clear pattern of vertical distribution up an inflorescence. Bumblebees taking nectar (Bombus hortorum visiting legally, and certain individuals of B. terrestris which positioned themselves head-upwards while taking nectar through holes bitten in the corolla) worked predominantly upwards on the racemose inflorescences of Linaria vulgaris, although the standing crop of nectar sugar per open flower increased up the raceme. Individuals of B. terrestris which robbed Linaria flowers in a head-down position worked predominantly downwards on inflorescences. The upward or downward directionality of intra-inflorescence movements by foraging insects may depend in part on the position these adopt during their flower visits.
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  • 8
    Electronic Resource
    Electronic Resource
    Springer
    Oecologia 51 (1981), S. 412-418 
    ISSN: 1432-1939
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Studies in Costa Rica on two ornithophilous flowers, Justicia aurea (Acanthaceae) and Columnea glabra (Gesneriaceae) showed a constancy of nectar solute concentrations that was attributed to microclimatic protection by the tubular corolla and to copious nectar secretion, helped by waterproofing by a lipid film on the nectar surface in Justicia and by preferential compass orientation of the flowers of Columnea. Most of the corollas in the patch of Justicia had been pierced by nectar-robbers. A consequence of this damage, together with local microclimate effects, was flower-to-flower variation in the amount and accessibility of nectar and in the nature and concentration of its minor components, notably amino acids. McDade and Kinsman's (1980) finding that nectar secretion could be suppressed by repeated sampling or by nectar-robbing was confirmed.
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  • 9
    Electronic Resource
    Electronic Resource
    Springer
    Entomologia experimentalis et applicata 71 (1994), S. 91-94 
    ISSN: 1570-7458
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
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  • 10
    Electronic Resource
    Electronic Resource
    Springer
    Entomologia experimentalis et applicata 94 (2000), S. 159-171 
    ISSN: 1570-7458
    Keywords: Drosophila ; induction ; habituation ; associative learning ; T-maze olfactometer
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Experiments reported in this paper investigate the properties of a change in the responsiveness of adult Drosophila melanogaster induced by exposure to different rearing media. This effect has previously been described as habituation or associative learning. Exposure to food medium containing 0.08% menthol induced a positive response to menthol odour in a T-maze olfactometer. A brief (one hour) exposure to mentholic food just before testing was sufficient to induce a change in responsiveness. The effect did not persist through periods of more than an hour of separation from mentholic medium. Effects induced by exposure to a single compound were not specific to that compound alone. Menthol-reared flies (MRFs) differed from plain reared flies (PRFs) in their responsiveness to the odours of benzaldehyde and ethyl acetate, as well as menthol, and exposure to ethyl acetate induced a change in response to menthol odour. That there was an induced positive response to menthol in MRFs suggests that conventional habituation is insufficient to explain the induced change in responsiveness, but the generalised nature of this behavioural induction in MRFs is hard to explain in terms of associative learning. The mechanism underlying the induction remains elusive.
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