a working model, embodying the preferential growth of lamellae parallel to the b-axis direction, and branching or interlamellar splaying hinged about the a-axis in the lamellae, is proposed for the precursor structures which have been observed to develop in the early stages of growth of pps spherulites in bulk polymer at crystallization temperatures in the range 270c-280c. the manifestation of transcrystallization at temperatures in the range 270c-280c has been used as a criterion for comparing the ability of various carbon fibers to nucleate crystallization in pps. whereas the originally surface treated pan-based low modulus (as4), and intermediate modulus (im7) fibers did not induce trans-crystallization at these temperatures, all the higher modulus pan-based (hms4, hmu) and pitch-based (p75s, p100s, p120s) fibers did cause its occurrence. with the exception of the hmu fibers, all the other high modulus fibers were originally surface treated in production. whether other factors, in addition to differences in graphitic order and crystallite size underlie the differences observed in the present study between nucleating ability of the higher modulus fibers as compared to the as4 and im7 fibers, remains an open question