We have shown that simple power-law dynamics is expected for flexible fractal objects. Although the predicted behavior is well established for linear polymers, the situationm is considerably more complex for colloidal aggregates. In the latter case, the observed K-dependence of (r) can be explained either in terms of non-asymptotic hydrodynamics or in terms of weak power-law polydispersity. In the case of powders (alumina, in particular) apparent fractal behavior seen in static scattering is not found in the dynamics. ID. W. Schaefer, J. E. Martin, P. Wiitzius, and D. S. Cannell, Phys. Rev. Lett. 52,2371 (1984). 2 J. E. Martin and D. W. Schaefer, Phys. Rev. Lett.