Isothermal crystallization of a low-molecular-weight poly(ethylene oxide) from both isotropic and structured melts at low undercoolings has been investigated via simultaneous measurements of small angle and wide angle X-ray scatterings (SAXS and WAXS). An evolution of the SAXS pattern was observed prior to the appearance of crystallinity determined through WAXS. A possible interpretation of this experimental observation is provided through the nucleation concept: primary nuclei exist in the melt due to localized large-amplitude density fluctuation sin the isotropic medium.