We report for the first time details of the morphology of alpha isotactic polypropylene transcrystallinity induced by aramid fibers as determined by high spatial resolution X-ray diffraction. We suggest that the parent lamellae nucleate at the fiber surface with the crystallite a*-axes parallel to the fiber axis, twist one quarter turn about the parent a axis within an approximate distance of 25 mu -m and then continue to grow without further twisting. This result is unexpected since lamellar twisting has never been observed in pure a spherulitic polypropylene.