  The addition of enough non-adsorbing polymer to an otherwise stable colloidal
suspension gives rise to a variety of phase behavior and kinetic arrest due to
the depletion attraction induced between the colloids by the polymers. We
report a study of these phenomena in a two-dimensional layer of colloids. The
three-dimensional phenomenology of crystal-fluid coexistence is reproduced, but
gelation takes a novel form, in which the strands in the gel structure are
locally crystalline. We compare our findings with a previous simulation and
theory, and find substantial agreement.
