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.