The methods described below are those commonly used in the study of living microbial mats. Coverage here is not exhaustive; for some methods not here discussed only literature references are indicated. The material here presented (including appended tabulations of data: Tables 20.5–20.7) is relevant to the studies discussed in Chapter 6.

Preserved and Sectioned Material of Whole Mat (J. D. Farmer)

Syringe cores (30 cc) of mat are subsampled by slicing with a razor blade, and are fixed in a mixture of 3% glutaraldehyde and 1% formalin in pond water immediately following collection. Dehydrated samples are infiltrated with Spurr's Low Viscosity Embedding Medium (Spurr 1969; Polysciences, Inc.) under vacuum for several hours. A two-step graded series, beginning with a 50:50 mixture of resin and 100% ethanol for 2 hours, was found to enhance penetration. The hard cure schedule recommended by Polysciences is followed in order to obtain the hardest embedment for thin sections. Embedments are prepared in plastic “peel-a-way” molds (Polysciences, Inc.) and cured at 70°C for 8 hours.

Sections (20 to 30 µm thick, in order to facilitate comparisons with thin sections of fossil stromatolites) are prepared by hand grinding, following a modification of standard petrographic methods (Nye et al. 1972). Organisms in sections prepared from Spurr's resin can be stained using a 1% solution of toluidine blue in distilled water. A 1% solution of alizarine red in dilute HC1 is an effective counterstain for detecting carbonate.