Holdfast of cells at age 17.5 min grown in A) PYE medium, B) PYE medium with 67% Percoll, C) PYE medium with 3.5% PEG 8000, D) PYE medium with 5% PEG 35000, E) PYE medium with 5% Dextran, and F) PYE medium with 10% Ficoll. Panels A, C, and E are fluorescence images, which clearly show the cell bodies in addition to the holdfasts. Panels B, D, and F are overlays of fluorescence and phase contrast images.