Figure 3. Flocculating cells are physically shielded from the external milieu.

A. Integral flocs were submerged in medium containing lethal levels of amphotericin B or ethanol. The flocs were subsequently sliced into thin sections and stained for viability using methylene blue, a dye that stains dead cells blue, while live cells remain white. (1) Control (no ethanol or amphotericin B); (2.) 100 µg ml⁻¹ amphotericin B for 45 minutes; (3) 70% ethanol for 1 minute; (4) 70% ethanol for 45 minutes. B. Flocs were first cut in half before they were subjected to a stress treatment. (5) Control, with 45 min. amphotericin B treatment prior to slicing and staining the floc (note that this control was not sliced in half prior to treatment); (6) sliced before treating with 70% ethanol; (7) sliced before treatment with 100 µg ml⁻¹ amphotericin B; (8) sliced before treatment with 15% ethanol. Note how for these intermediate conditions (7 and 8), cells that were originally situated in the heart of the floc (right-hand edge of specimens) are stained less than cell at the original periphery, but more than cells that remained shielded within the floc during stress treatment.