Macroscopic pattern formation by P. vortex on MH agars. In all pictures the lighter areas are interconnected (moving) masses of cells and darker areas are uncolonized agar; all pictures taken after 18 h from Petri-dish-wide colonies. A. Swarming on 1.5% (w/v) agar MH plates from a point inoculation showing fractal pattern and (centrally) detached colonies. B. Swarming on 0.3% (w/v) agar MH plates after 28 h in which a network forms across the plate then elaborates. C. Detail of inoculation from a droplet on 0.3% agar with outgrowth at specific points from the central circular mass. D. Detail of pattern 30 mm from the center from the same plate as (C). Scale bar in (B) represents 2 cm when applied to panels (A) or (B) and 2 mm for (C) or (D).