It is shown that the modern synergy viewpoint on striations offers an explanation of how backward, forward, and fixed ionization waves (striations) in a direct current (dc) gas discharge come into being. Striations always propagate in the direction of majority carriers, namely, electrons with respect to the stationary ion skeleton, but particular experimental conditions in gas discharge tubes associated with cataphoretic and electrophoretic phenomena determine the actual propagation direction of striations. Published under license by AIP Publishing.