Figure: : Evolution from a gap 1 pair.
Rule 22 is a rule which acts somewhat like a binary counter, in the sense that isolated cells expand, generating regions whose interiors periodically vanish, leaving the frontier cells to expand anew. These new sites of expansion eventually collide, possibly leaving the whole new interior vacant. Properly synchronized, the binary counter effect ensues. Rule 22 has an especial tendency towards binary counters, notably amongst configurations evolving from single pairs of live cells. Figures and show boundary collisions leaving gaps of 1 and 2 respectively
Compatibility with a finite cycle length implies constraints which exclude certain mutual separations; most work, the rest vanish after a while or convert into other patterns. The majority of the cycles of length 16 fit this pattern; scrutiny of the figures reveals a variety of interactions amongst advancing boundaries, also the systematic depletion of the interiors.