Rates of relaxation of polymer chains of high molecular weight preclude extensive configurational rearrangements of long range in the process of crystallization from a melt. Analyses of neutron scattering functions for deuterated polyethylene and polypropylene chains dispersed with the corresponding protonated host in the melt and co-crystallized therewith show that adjacent re-entry occurs infrequently. The highly entangled topological relationships of chains that exist in the melt must be retained, in large measure, in the semicrystalline state. Crystallization from dilute solution is concluded to involve participation of a number of chains competing for deposition at growth kinks. High molecular weight chains in these solution-grown crystals are thus distributed in a number of neighbouring growth layers, the crystalline stems being connected predominantly by non-adjacent folds.