Different convection dynamics in mixtures with the same separation ratio.

We report on convection near threshold in circular samples of radial aspect ratio {Gamma}=11.5 using ethanol-water mixtures with two concentrations {ital x}, but with the same separation ratio {Psi}{approx_equal}{minus}0.08. For {ital x}=0.250, convection begins with transients that lead to a time-independent cell-filling state, typically in a day. For {ital x}=0.011, there is a range of temperature differences where repeated transients and aperiodically fluctuating localized regions of disordered convection persist for many days. In rare cases these lead to an apparently stable {open_quote}{open_quote}wall{close_quote}{close_quote} state of traveling waves surrounding pure conduction. {copyright} {ital 1996 The American Physical Society.}