Keep in mind that cane-cut contemporaries (as this one is) are made by the same process as vintage pieces. So the ridges are caused by the same processes. Those can be a twist imparted to the cane before or during the cut - or by the rounding process.
Here is Geoff Beetem making a cane cut piece - which may illustrate the basic process and help you visualize how the ridge can be created. Remember: most cane-cut designs are intentionally twisted to cause the ribbons, latticino to spiral (Geoff makes PERFECT pieces )