Fig. 2. (A) Plan view of a steady state bioconvective pattern prepared for Fourier analysis as described in Materials and methods. A typical pattern developed under control gravity (1.01 g) in a suspension of T. pyriformis (1x10⁶ cells ml^-1 in a 4 mm deep glass chamber). Regions of higher cell densities appear as bright white areas under dark field illumination. Bar, 10 mm. (B) 2D FFT of A after applying a Hann window filter. (C) Radial spectrum density of the pattern in B (solid line) as a function of wave number (per 72.5 mm) and the result of least-squares fitting of an unnormalized biased Gaussian function (broken line) (r²=0.92, P<0.001). (D) 2D FFT of the image recorded under hypergravity (2.09 g), which is shown in Fig. 3A. (E) Radial spectrum density of the pattern in D (solid line) and the result of least-squares (broken line) (r²=0.97, P<0.001).