Aggregation in Polysphondylium.

Dense aggregating fields of P. violaceum and P. pallidum exhibit propagated waves which may be analogous to those seen in Dictyostelium discoideum. As in D. discoideum the wave velocity is determined by an intracellular delay between stimulation and response, rather than by the diffusion coefficient of the acrasin. The frequency of the propagated wave overlaps that of aggregating D. discoideum, so that absence of coaggregation reported by Raper & Thom is unlikely to be based on specificity of the propagated wave parameters, but rather on a difference in the chemical acrasin itself, as argued on independent evidence by Bonner. Despite this difference in the chemical nature of the acrasin, the presence of propagated waves in Polysphondylium with frequencies similar to those in D. discoideum, taken together with evidence for a diffusible acrasin, suggests that the mechanism of aggregation is substantially the same in both genera.