Structural evolution of poly(L-lactide) during cold-crystallization at 80 degrees C was examined via simultaneous small/wide-angle X-ray scattering (SAXS/WAXS), Fourier-transform infrared spectroscopy (FTIR), and differential scanning calorimetry (DSC). The incipient alpha' crystals of loosely packed 10(7) helices, formed at t(c) = 200 s as detected via both WAXS and FTIR, were hardly identifiable via SAXS or DSC due to its low values of density contrast or latent heat (initially Delta H-alpha' approximate to 12 J/g, gradually reaching 74 J/g near the end of crystallization, in contrast to Delta H-alpha approximate to 140 J/g), was already large in lateral size (with coherence length Lambda(200/110) approximate to 35 nm, increasing to 50 am during t(c) = 200-400 s and remained little changed afterward). Once formed, the alpha' crystals underwent continuous and persistent perfection for decreasing lattice spacing and partially transformed to smaller alpha crystals (t(c) approximate to 800-1800 s, up to a saturated population ratio of 1:4 between alpha and alpha' phases), followed by slower yet steady increases in SAXS invariant without significant changes in the alpha and alpha' contents for t(c) > 1800 s. It is concluded that the alpha' form is a transient structure of continuously increasing packing density and latent heat toward the alpha form, reminiscent of the mesomorphic phase as precursors to stable crystals in other polymers. Nevertheless, transformation to alpha crystals occurred when the lattice parameters of the alpha' phase were closer but still finitely different from those of the alpha phase and that the conversion between the two phases was limited in this isothermal case. Both observations suggest that, in spite of the transient nature of the alpha' phase, the final transformation step to the stable alpha form is still achieved via a first-order route.