  We track the secondary bifurcations of coherent states in plane Couette flow
and show that they undergo an incomplete periodic doubling cascade that ends
with a crisis bifurcation. We introduce a symbolic dynamics for the orbits and
show that the ones that exist fall into the universal sequence described by
Metropolis, Stein and Stein for unimodal maps. The periodic orbits cover much
of the turbulent dynamics in that their temporal evolution overlaps with
turbulent motions when projected onto a plane spanned by energy production and
dissipation.
