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An ultrastructural study of crossbands isolated from Caulobacter crescentus Sk1 418 stalks permitted a view of these structures in a plane other than the perpendicular view normally presented in the electron microscope. These crossbands were composed of concentrically arranged, alternating light and dark bands when stained with phosphotungstic acid. Evidence supports the hypothesis that crossbands appear to compose a structural barrier extending the width of the stalk and may function to support unit membrane extending the length of the stalk.

Slime layers are being studied in our laboratories in an attempt to understand their functions in the control of pollution in natural streams. A method for fixing, staining, and embedding microorganisms in the intact slime has been developed. In this method, epoxy resin discs are placed in a holder and are introduced into a simulated stream. After various periods of time the discs are punched out of the holder into the fixative. The disc with the attached slime is fixed, stained (4% osmium tetroxide plus ruthenium red), dehydrated, and embedded in epoxy resin so that thin sections can be cut through the vertical plane of the slime mass. Such thin sections permit detailed examination of the attached layer, the surface-slime interface, the spatial relationships between cells in the vertical slime structure, and the strands of extracellular material between and around cells. No special attachment structures were noted as the cells appeared to be attached to the surface by extracellular material alone. This material was observed in strands and netlike forms between cells which are positioned 1 to 4 mum apart in the slime.