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Digitale Medien

The preparation and structure of barium uranium oxide BaUO3+x (1982)

Barrett, S. A. ; Jacobson, A. J. ; Tofield, B. C. ; [weitere]

Copenhagen : International Union of Crystallography (IUCr)

Acta crystallographica 38 (1982), S. 2775-2781

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ISSN: 1600-5740

Quelle: Crystallography Journals Online : IUCR Backfile Archive 1948-2001

Thema: Chemie und Pharmazie , Geologie und Paläontologie , Physik

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1107/S0567740882009935

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Ice Crystals and Filaments (1880)

BARRETT, S. T.

[s.l.] : Nature Publishing Group

Nature 21 (1880), S. 537-537

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ISSN: 1476-4687

Quelle: Nature Archives 1869 - 2009

Thema: Biologie , Chemie und Pharmazie , Medizin , Allgemeine Naturwissenschaft , Physik

Notizen: [Auszug] SOMETHING very like the “comb-like masses of ice” appears upon the surfaces of plaster-models such as dentists make, after they have been coated with a preparation called Liquid Silex; except that it is finer and woolly. It seems to be caused by the contraction of the models forcing out very ...

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1038/021537c0

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3

Digitale Medien

Variation of pollen limitation in the early flowering Mediterranean geophyte Narcissus assoanus (Amaryllidaceae) (2000)

Baker, A. M. ; Barrett, S. C. H. ; Thompson, J. D.

Springer

Oecologia 124 (2000), S. 529-535

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ISSN: 1432-1939

Schlagwort(e): Key words Fruit and seed set ; Narcissus assoanus ; Pollen limitation ; Reproductive ecology ; Seed:ovule ratios

Quelle: Springer Online Journal Archives 1860-2000

Thema: Biologie

Notizen: Abstract A recent literature review indicates that pollen limitation of female fertility is a common feature of flowering plants. Despite the ecological and evolutionary significance of pollen limitation, most studies have only examined fertility in a single population at one time. Here we investigate pollen limitation of fruit and seed set in five populations of Narcissus assoanus, a self- sterile, insect-pollinated geophyte, over 2–3 years in southern France. In common with many early spring flowering plants, pollinator visitation to N. assoanus is often infrequent. Supplemental hand-pollination of flowers with outcross pollen significantly increased overall fruit and seed set by 11% and 19%, respectively. Four of the five populations experienced some pollen limitation during the study. For a given year, there was significant variation in pollen limitation among populations. Two of the populations were pollen limited in one year but not in other years in which they were studied. Seed:ovule ratios for open- and hand-pollinated flowers averaged 0.29 and 0.33, respectively. While hand pollination significantly increased the seed:ovule ratio, the low value obtained indicates that the majority of ovules in flowers do not mature seeds despite hand pollination. The role of genetic and environmental factors governing low seed:ovule ratios in N. assoanus is discussed.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1007/s004420000417

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4

Digitale Medien

Trimorphic incompatibility in Eichhornia azurea (Pontederiaceae) (2000)

Bianchi, M. ; Vesprini, J. ; Barrett, S. C. H.

Springer

Sexual plant reproduction 12 (2000), S. 203-208

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ISSN: 1432-2145

Schlagwort(e): Key words Tristyly ; Trimorphic incompatibility ; Pollen trimorphism ; Partial incompatibility ; Clonal aquatic plant

Quelle: Springer Online Journal Archives 1860-2000

Thema: Biologie

Notizen: Abstract Eichhornia azurea (Pontederiaceae) is a mat-forming, clonal aquatic that inhabits lakes, marshes and river systems in many parts of the Neotropics. The species is tristylous with long-, mid-, and short-styled morphs commonly represented in natural populations. To investigate whether E. azurea possesses a trimorphic incompatibility system typical of tristylous species, we conducted a controlled pollination experiment on 15 clones representing the three style morphs from a natural population near Rosario, Argentina. Comparisons of fruit and seed set following self-, illegitimate, and legitimate pollinations clearly demonstrated the presence of trimorphic incompatibility in E. azurea. Self- and illegitimate pollinations produced significantly less fruit and seed than legitimate pollinations in all three style morphs. Pollen from the two anther levels within a flower exhibited contrasting compatibility relations in self-pollinations. In common with several other tristylous species in Pontederiaceae, the expression of self-incompatibility was weakest in the mid-styled morph and strongest in the short-styled morph. We discuss the ecological and evolutionary significance of the partial expression of trimorphic incompatibility in E. azurea.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1007/s004970050001

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5

Digitale Medien

Heterostyly in the Lamiaceae: The case ofSalvia brandegeei (2000)

Barrett, S. C. H. ; Wilken, D. H. ; Cole, W. W.

Springer

Plant systematics and evolution 223 (2000), S. 211-219

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ISSN: 1615-6110

Schlagwort(e): Heterostyly ; distyly ; zygomorphic flowers ; self-compatibility ; protandry ; geitonogamy ; Lamiaceae ; rare plant species

Quelle: Springer Online Journal Archives 1860-2000

Thema: Biologie

Notizen: Abstract Heterostyly rarely occurs in families with strongly zygomorphic flowers. For this reason Darwin (1877) doubted whether heterostyly would occur in the Lamiaceae and recent reviews have not reported the floral polymorphism in this family. Here we describe distyly in a rare species ofSalvia restricted to bluffs and seaward canyons on Santa Rosa Island (Santa Barbara Co., California) and northwestern Baja California (Mexico).Salvia brandegeei is morphologically distylous with populations composed of equal frequencies of long-and short-styled morphs differing reciprocally in stigma and anther position. Controlled hand pollinations demonstrated no significant differences in the seed set of self, intramorph or intermorph pollinations. Unlike most heterostylous species investigated,S. brandegeei does not possess diallelic incompatibility or ancillary polymorphisms of pollen and stigmas. We propose that the evolution of distyly inS. brandegeei may have been associated with an ecological shift to a new environment in which protandry failed to prevent increased levels of geitonogamy. Heterostyly was then selected because it increased the proficiency of cross-pollination. The origin of distyly in self-compatibleS. brandegeei is consistent with Lloyd and Webb's theoretical model for the evolution of distyly.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1007/BF00985280

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