FIG. 1.

Swarm cell tracking. The top image is a phase-contrast video image of an E. coli swarm. The lower image is a computer display in which the heading of each cell is indicated by the color of a line running from its head to tail. For example, cells moving toward the right are magenta, toward the top are blue, toward the left are green, and toward the bottom are yellow. The coloring changes as a cell's trajectory changes, but each cell's identity remains fixed.