50 research outputs found
Staminal Vascular Architecture in Five Dicotyledonous Angiosperms
Staminal vasculature is usually depicted as a single bundle extending unchanged through the filament and ending at some level in the anther. Because some authors have suggested that this view is oversimplified, stamens of five dicot species were studied in detail. The basifixed anthers of Asarum canadense, Drimys winteri, and Isopyrum biternatum have a single vascular bundle which becomes dilated in the connective, along with other specializations which vary from species to species. Pyrus sp. and Prunus virginiana have dorsifixed anthers in which the filament bundle branches after entry into the anther. The extent of branching, and the internal architecture of the bundles, varies with the form of the stamen
Non-equilibrium dynamics and floral trait interactions shape extant angiosperm diversity.
Why are some traits and trait combinations exceptionally common across the tree of life, whereas others are vanishingly rare? The distribution of trait diversity across a clade at any time depends on the ancestral state of the clade, the rate at which new phenotypes evolve, the differences in speciation and extinction rates across lineages, and whether an equilibrium has been reached. Here we examine the role of transition rates, differential diversification (speciation minus extinction) and non-equilibrium dynamics on the evolutionary history of angiosperms, a clade well known for the abundance of some trait combinations and the rarity of others. Our analysis reveals that three character states (corolla present, bilateral symmetry, reduced stamen number) act synergistically as a key innovation, doubling diversification rates for lineages in which this combination occurs. However, this combination is currently less common than predicted at equilibrium because the individual characters evolve infrequently. Simulations suggest that angiosperms will remain far from the equilibrium frequencies of character states well into the future. Such non-equilibrium dynamics may be common when major innovations evolve rarely, allowing lineages with ancestral forms to persist, and even outnumber those with diversification-enhancing states, for tens of millions of years
Aquilegia, Vol. 37 No. 6, Winter 2013, Newsletter of the Colorado Native Plant Society
https://epublications.regis.edu/aquilegia/1146/thumbnail.jp
Os perigos da utopia
<!--[if gte mso 9]><xml> <w:WordDocument> <w:View>Normal</w:View> <w:Zoom>0</w:Zoom> <w:HyphenationZone>21</w:HyphenationZone> <w:PunctuationKerning /> <w:ValidateAgainstSchemas /> <w:SaveIfXMLInvalid>false</w:SaveIfXMLInvalid> <w:IgnoreMixedContent>false</w:IgnoreMixedContent> <w:AlwaysShowPlaceholderText>false</w:AlwaysShowPlaceholderText> <w:Compatibility> <w:BreakWrappedTables /> <w:SnapToGridInCell /> <w:WrapTextWithPunct /> <w:UseAsianBreakRules /> <w:DontGrowAutofit /> </w:Compatibility> <w:BrowserLevel>MicrosoftInternetExplorer4</w:BrowserLevel> </w:WordDocument> </xml><![endif]--><!--[if gte mso 9]><xml> <w:LatentStyles DefLockedState="false" LatentStyleCount="156"> </w:LatentStyles> </xml><![endif]--><!--[if gte mso 10]> <style> /* Style Definitions */ table.MsoNormalTable {mso-style-name:"Tabela normal"; mso-tstyle-rowband-size:0; mso-tstyle-colband-size:0; mso-style-noshow:yes; mso-style-parent:""; mso-padding-alt:0cm 5.4pt 0cm 5.4pt; mso-para-margin:0cm; mso-para-margin-bottom:.0001pt; mso-pagination:widow-orphan; font-size:10.0pt; font-family:"Times New Roman"; mso-ansi-language:#0400; mso-fareast-language:#0400; mso-bidi-language:#0400;} </style> <![endif]--> <p class="MsoNormal"><span>A utopia pode ter um lado que eleva e um lado sinistro, mas geralmente o lado sinistro acaba destruindo o idealismo inicial. A raz&atilde;o para isto &eacute; que os ut&oacute;picos inevitavelmente adotam uma imagem messi&acirc;nica do mundo. As tr&ecirc;s revolu&ccedil;&otilde;es messi&acirc;nicas na hist&oacute;ria&mdash;a americana, a francesa e a bolchevique&mdash;foram lideradas por homens que pensavem que suas id&eacute;ias eram universais. Este ensaio examina os escritos do existencialista franc&ecirc;s Albert Camus, que argumenta que n&atilde;o existem valores transcendentais, ao mesmo tempo que ele n&atilde;o aceita o niilismo. Camus faz uma distin&ccedil;&atilde;o entre um rebelde e um revolucion&aacute;rio, e conclui que uma rebeli&atilde;o tentar&aacute; terminar com uma opress&atilde;o esped&iacute;fica, enquanto que uma revolu&ccedil;&atilde;o tentar&aacute; criar &ldquo;um novo homem com valores comuns ao mundo inteiro.</span></p>
The dangers of Utopia
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