Orientation of Drawer Bottoms

[rchampagne]

I am building some Newport drawers, most of which have bottoms nailed on to the drawer sides and back (the front is let into a dado), then runners get applied to the drawer bottoms.  Which way is the grain oriented on originals (this seems to have been a somewhat common practice, at least around here in New England)?  If I run the grain front to back, do I need to leave some room for expansion near the drawer sides, or should I made the bottoms flush with the drawer sides?
Thanks,
Rob