A directional melting experiment of a rectangular sheer of Ga-5wt% In in a horizontal temperature gradient is described. Real-time radioscopy is used to visualize in situ the solid structure, the interface morphologies, and the flow patterns. Information on unstable double-diffusive convection layers, their time-dependent characteristics of formation, growth, and merging, are obtained. Go-existence of convection and conduction layers in the melt, the interaction between double-diffusive convection layers, the development of solute stratification in the melt, and the dynamic solid/liquid interface morphologies are discussed.