The field of palynology is reviewed in terms of its contributions to angiosperm systematics and phytogeny. Principal pollen characters which are phylogenetically useful at higher taxonomic levels (mcluding aperture type, pollen wall architecture, pollen-unit, polarity fymmetrv shape, and gram size), and their evolutionary trends are examined. Many palynologS characters and concepts are subjected to re-examination, particularly in an Lktionarp hylogenetic context. An attempt is made to show how pollen characters correlate wUh various higher categories of the Takhtajan and Cronquist systems of angiosperm cSfcation and to out hne certain phylogenetic trends observed in the pollen of different groups of angLpenns With some exceptions, pollen morphology is consistent with the levels of rektive ZS and the relationships^ postulated in the Takhtajan and Cronquist systems. AngLsper^ no lien grains are clearly divisible into two fundamentally different types (each X s ! derivatives): heteropolar, bilateral, boat-shaped monosulcate pohen versus islpokr ra d7o tvoeT 6 hT; g l 0l T V"?? e P f 6n u " G >™Pe™ous" monoLcate po Ien and derivate" type (ulcerate disulculate, etc.) characterize both the putatively primitive dicotySonous subdass Magnohidae and the monocotyledons. The six non-magnoliid dicotyledonous ubcW on the other hand are characterized by tricolpate pollen and derivative ty^Tw^SS' tnporate, rugate, etc.). Relatively primitive tricolpate pollen is retained by many ^nuZmle, J J. W. Walker wishes to thank directors and curators of the following herbaria for use of penological I material from their collections, with special thanks to indiviSsTsted Gray G ^ de a n l Znl a uf ^arionTl^ t^ ^T^' ^ Unl ™«* New LrfLaS waraen, Bronx U.i>.
The PHENIX detector is designed to perform a broad study of A-A, p-A, and p-p collisions to investigate nuclear matter under extreme conditions. A wide variety of probes, sensitive to all timescales, are used to study systematic variations with species and energy as well as to measure the spin structure of the nucleon. Designing for the needs of the heavy-ion and polarized-proton programs has produced a detector with unparalleled capabilities. PHENIX measures electron and muon pairs, photons, and hadrons with excellent energy and momentum resolution. The detector consists of a large number of subsystems that are discussed in other papers in this volume. The overall design parameters of the detector are presented. The PHENIX detector is designed to perform a broad study of A-A, p-A, and p-p collisions to investigate nuclear matter under extreme conditions. A wide variety of probes, sensitive to all timescales, are used to study systematic variations with species and energy as well as to measure the spin structure of the nucleon. Designing for the needs of the heavy-ion and polarized-proton programs has produced a detector with unparalleled capabilities. PHENIX measures electron and muon pairs, photons, and hadrons with excellent energy and momentum resolution. The detector consists of a large number of subsystems that are discussed in other papers in this volume. The overall design parameters of the detector are presented. Disciplines Engineering Physics | Physics Comments This is a manuscript of an article from Nuclear Instruments and Methods in Physics Research
In the last decade significant new information has been gained about the early evolution of flowering plants through studies of Early Cretaceous angiosperm pollen and the pollen of living primitive flowenng plants. Although most recent palynological studies of extant primitive angiosperms have used both scanning and transmission electron microscopy, few ultrastructural studies of early fossil aneioSDerm nollen erains pvict Thic r.an»r â"¢r^ro,o^«to « * * i.. ^li. _-^.._^.-tu:-* Cretaceous angiosperm Fredericksburgian of Ol yumupouennes nugnesii. two att. ClavatipoUenites species, Asteropollis asteroides. Stephanocolpites Jredencksburgensis, Retimonocolpites dividuus, R.peroreticulatm, two aff. Retimonocolpites species, StellatopoUis barghoornii, and three species of Liliacidites. These grains were investigated using a technique that we have developed for working with single fossil pollen grains by which we are able light-mic] known ' 7^ r""-" e^«x*xa, oui^ii aa muse luui cunsiiLuic me DUiK oi inc earuesi kiiuwu yai^. 01 the tossil record of the flowering plants, and provides a much improved means of deUmiting Early angiosperm pollen form uur study also reveals that a close similarity exists between some Early Cretaceous angiosperm pollen and pollen produced by certain living primitive angiosperms. ClavatipoUenites hughesii, Asteropollis asteroides, and Stephanocolpites fredericksburgensis exhibit varying degrees of similarity at the ultrastructural level respectively to pollen of the extant angiosperm genera Ascarina. Hedyosmum. and Chloranthus. all three of which belong to the modem family Chloranthaceae. Pollen described under
DNA methylation regulates eukaryotic gene expression and is extensively reprogrammed during animal development. However, whether developmental methylation reprogramming during the sporophytic life cycle of flowering plants regulates genes is presently unknown. Here we report a distinctive gene-targeted RNA-directed DNA methylation (RdDM) activity in the Arabidopsis thaliana male sexual lineage that regulates gene expression in meiocytes. Loss of sexual-lineage-specific RdDM causes mis-splicing of the MPS1 gene (also known as PRD2), thereby disrupting meiosis. Our results establish a regulatory paradigm in which de novo methylation creates a cell-lineage-specific epigenetic signature that controls gene expression and contributes to cellular function in flowering plants.
Following the acceptance of plate tectonics theory in the latter half of the 20th century, vicariance became the dominant explanation for the distributions of many plant and animal groups. In recent years, however, molecular-clock analyses have challenged a number of well-accepted hypotheses of vicariance. As a widespread group of insects with a fossil record dating back 300 My, cockroaches provide an ideal model for testing hypotheses of vicariance through plate tectonics versus transoceanic dispersal. However, their evolutionary history remains poorly understood, in part due to unresolved relationships among the nine recognized families. Here, we present a phylogenetic estimate of all extant cockroach families, as well as a timescale for their evolution, based on the complete mitochondrial genomes of 119 cockroach species. Divergence dating analyses indicated that the last common ancestor of all extant cockroaches appeared ∼235 Ma, ∼95 My prior to the appearance of fossils that can be assigned to extant families, and before the breakup of Pangaea began. We reconstructed the geographic ranges of ancestral cockroaches and found tentative support for vicariance through plate tectonics within and between several major lineages. We also found evidence of transoceanic dispersal in lineages found across the Australian, Indo-Malayan, African, and Madagascan regions. Our analyses provide evidence that both vicariance and dispersal have played important roles in shaping the distribution and diversity of these insects.
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