For dowels the edge grain goes against the bow but for safety sake the grain "flames" should point forward so that usually leaves only one side.
I learned about putting the stiff side against the bow from Art Butner(artcher1). Art is the best, by far, arrow maker I've ever known and a very generous person to boot. He taught me how to make cane, sourwood shoot arrows and snaky arrows but he also totally hand made doweled arrows with hand tools,even the 4 point footings and self nocks.