Fig. 1. Gravity-dependent pattern formation of Tetrahymena pyriformis enclosed in a circular glass chamber 2 mm deep at a density of 1.0x10⁶ cells ml^-1. (A) Plan view of the suspension under subcritical (a), threshold (b) and supracritical (c) conditions for pattern formation with increase in gravity. Regions with higher cell densities appear as bright white areas under dark field illumination. A linear region indicated by faced arrows is the portion on which space-time plots in (B) and (C) were made. Bar, 10 mm. (B) Space-time plot of an experiment of increasing gravity and the corresponding gravity profile. Letters a-c indicate the time corresponding to respective plan views a-c shown in A. (C) Space-time plot of an experiment of decreasing gravity and the corresponding gravity profile. Horizontal and vertical bars in B and C are 1 min and 10 mm, respectively. Broken lines in B and C indicate threshold levels for increasing and decreasing gravity, respectively.