A set of isothermally melt-crystallized polyethylene samples was examined using small angle x-ray scattering (SAXS). Time and temperature of crystallization were the variable parameters used to create the set of samples. This study, coupled with data obtained from polyethylene single crystals, produced information concerning the extrapolation of single-crystal data to fit bulk systems. This study also suggests that the surface energy of the mature crystals is always lower than that of the nucleated state and/or the nucleation factor K sigma en increases with decreasing supercooling. -- AATA