  I argue that in open-string theory with hierarchically small (or large) extra
dimensions, gauge groups can unify naturally with logarithmically-running
coupling constants at the high Kaluza-Klein (or string-winding) scale.
  This opens up the possibility of rescuing the standard logarithmic
unification at $M_U\sim 10^{15-18}$ GeV even if the fundamental-string scale is
much lower, at intermediate or possibly even electroweak scales. I also
explain, however, why a low type-I string scale may not suffice to obliterate
the ultraviolet problems usually associated with the gauge hierarchy.
