Fig. 7. Frequency distribution of the period of optical density waves in early aggregation and in the mound stage. The data were divided into classes with a width of 40 seconds and normalised to account for the different number of measurements. (A) Period of darkfield waves during early aggregation. DH1 shows the shortest period, whereas all the other mutants are shifted towards the longer periods. (B) Period of waves in the mound stage. The periods are generally shorter in the mound stage, however the mutants still have longer periods.