Adaptability of Scanning Electron Microscopy to Studies of Pollen Morphology

We have explored methods to achieve excellent results in study of the pollen grain wall by using only one electron microscope, the scanning electron microscope (SEM). While the secondary electron imaging mode, the most common in use, has great value in characterizing the exine surface it is possible to obtain a more comprehensive representation of pollen grain walls by expanding the capability of the secondary mode and making use of backscatter and transmission imaging detectors. In this way information is obtained about internal exine features that are likely to be more stable phylogenetically than the generally late-to-form surface structure. We illustrate the usefulness of natural and induced fractures, cryornicrotomy, thin-section examination, section deplasticization, localized acetolysis and pollen erosion by ionic bombardment in imaging exine structure. Techniques for expanding the use of SEM in taxonomic studies of mature pollen grain walls are outlined in flow chart sketches and illustrated with numerous examples from angiosperm pollen

United States Senate Catalogue of Graphic Art

This volume is the first comprehensive publication of the almost one thousand prints in the holdings of the United States Senate. The collection represents a 30-year effort to document graphically the 19th and early 20th century history of the Senate, the Capitol, and American political history. The diverse illustrations range from inauguration ceremonies and impeachment trials to senatorial portraits and political cartoons. Represented in the Senate\u27s graphic art collection are some of the most notable artists who worked in the printmaking medium: Augustus Kallner, Rembrandt Peale, Alexander Hay Ritchie, Thomas Nast, and Joseph Keppler. While visually engaging, these prints also are important primary historical records. By carefully scrutinizing a print, in the same way a historian might analyze a journal or diary, one can extract the meaning of the artist and decode the historical subtext. Often, the elements omitted by the artist in an image are just as important as those that are included. As a research tool, the graphic art collection has been invaluable to historians and scholars for many years. This publication seeks to broaden the appeal of the collection by making the information available to a wider audience. Essays by Senate Curator Diane K. Skvarla and Associate Senate Historian Donald A. Ritchie provide an overview of the collection, with selected prints highlighted throughout the book. This is the second volume dedicated to the Senate\u27s art and historic collections. In 2002 the Senate published the United States Senate Catalogue of Fine Art, presenting the 160 paintings and sculptures in the Senate\u27s fine art collection

On the prediction of hydrophobic coagulation by the extended DLVO model

Parshley i Israelachvili [Colloids Surfaces, 2, 169, 1981] zastosowali proste wyrażenie wykładnicze krótkiego zasięgu do przybliżonego opisu energii potencjalnej oddziaływań hydrofobowych pomiędzy dwoma płytkami miki. Mika użyta do badań była hydrofobizowana poprzez adsorpcję in situ kationowego surfaktanta. Wyeliminowali oni współczynnik przed wyrażeniem wykładniczym dzięki użyciu prostego równania Li i Neumanna [J. Colloid and Interface Sci., 137, 304 (1990)] pozwalającego na obliczania napięcia międzyfazowego. Dla zweryfikowania modelu rozszerzonej teorii DLVO dla hydrofobowej koagulacji przeprowadzono serię eksperymentów z wodną zawiesiną drobnych ziaren syderytu, które stopniowo hydrofobizowano poprzez adsorpcję oleinianu sodu przy dwóch siłach jonowych. Dodatkowo, wyznaczono eksperymentalnie takie parametry modelu jak potencjał dzeta oraz kąt zwilżania wodą. Uzyskano zadawalającą korelację (R≈0.99) pomiędzy napięciem elektrycznym na fotodiodzie, będącym względną eksperymentalną miarą stopnia koagulacji hydrofobowej, które rejestrowano po zadanym czasie sedymentacji suspensji syderytu, oraz teoretycznie obliczonym maksimum całkowitej energii potencjalnej koagulacji. Przetestowano również dwa inne, dostępne w literaturze, wyrażenia na oddziaływania hydrofobowe dalekiego zasięgu, które wykazały słabą korelację z danymi ksperymentalnymi.A single short-range exponental, obtained for two mica sheets hydrophobized by in situ adsorption of cationic surfactants [Pashley and Israelachvili, Colloids Surfaces, 2, 169 (1981)], was used to approximate the hydrophobic interaction potential energy. The prefactor of the exponential was estimated by using a simple equation of state for interfacial tensions [Li and Neumann, J. Colloid Interface Sci., 137, 304 (1990)]. To verify the simple extended DLVO model of hydrophobic coagulation, a series of experimental tests on a fine siderite suspension with particles gradually hydrophobized by adsorption of sodium oleate surfactant was performed at two ionic strengths. The model parameters (ζ potential and water contact angle) of the siderite particles were determined experimentally. A satisfactory (R≈0.99) correlation between the photodiode voltage, detected after a selected period of time of the siderite suspension sedimentation being an experimental measure of the extent of hydrophobic coagulation, and the theoretically calculated total potential energy maximum was obtained. Two other long-range exponential expressions of the hydrophobic interaction available in the literature were also tested, which provided a poor correlation with the presented experimental results

Pollen Morphology: The Potential Influence in Higher Order Systematics

Volume: 66Start Page: 633End Page: 70

Pollen Morphology of Saprophytic Taxa in the Gentianaceae

Volume: 56Start Page: 420End Page: 43

Genera of the Vernonieae (Asteraceae) of China with a Study of Their Pollen

The genera and species of Vernonieae in China are reviewed using revised generic concepts. The recognized genera are Acilepis, Baccharoides, Camchaya, Cyanthillium, Decaneuropsis, Distephanus, Elephantopus, Ethulia, Gymnanthemum, Khasianthus, Monosis, Pseudelephantopus, Strobocalyx, and Tarlmounia. The pollen of each genus is described and illustrated. Keys are provided to genera and species

A New Monotypic Genus, Ananthura , from Tropical Africa (Asteraceae, Vernonieae)

Volume: 21Start Page: 251End Page: 25

Systematic Implications from Electron Microscopic Studies of Compositae Pollen-A Review

Volume: 53Start Page: 220End Page: 25