Etched sections of agates examined by scanning electron microscopy show three types of compositional zonation'. (1) two-unit oscillatory sequences in which the successive zones are of the same width, on a micron scale, but show a uniform difference in the content of (OH) in structural sites; (2) three-unit oscillatory sequenc€s of various palindromic types in which successive zones are of the s...

Despite being a harsh environment, sand dunes are rich in invertebrates, with about 30% (188 species) of the British spider fauna represented (Duffey, 1968), and 53 species being strongly associated with coasts (Ratcliffe, 1977). Arachnologists have examined spider communities in relation to the seral succession of plant communities on sand dunes (e.g. Lowrie, 1948; Barnes, 1953; Perttula, 1984...

Changes in freshwater inflow can cause changes in the distribution and diversity of marsh vegetation in estuarine habitats. In the fall of 2002 bankside vegetation was surveyed along the 24 km length of the Altamaha River estuary (n= 14 sites). Sites were quantified for multiple plant and edaphic parameters, including plant density, height, and tiller diameter. In this paper we present the char...

We have developed a perfusion bioreactor system that allows the formation of steady state oxygen gradients in cell culture. In this study, gradients were formed in cultures of rat hepatocytes to study the role of oxygen in modulating cellular functions. A model of oxygen transport in our flat-plate reactor was developed to estimate oxygen distribution at the cell surface. Experimental measureme...