The absence of a discommensuration lattice in the incommensurate phase of

X-ray scattering close to the lock-in temperature has been measured as a function of temperature to investigate whether the discommensuration lattice is a useful description of the structure of . We review different models for the incommensurate structure and discuss how they might be distinguished by a scattering experiment. Our results are compared with earlier published x-ray measurements and with those obtained from nuclear spin-resonance techniques. All of the x-ray results suggest that higher harmonics of the scattering measured in the and planes are much weaker than predicted by the abrupt-discommensuration model. We conclude from the measurements that this theory does not provide an adequate description of the experimental results close to the lock-in transition.