This may be achieved by using the outer, under-bark surface of the tree as the back of the bow (convenient with most white woods), or by the painstaking process of removing outer growth rings (often used with yew and osage orange), or by making or following a cut or split surface which happens to have continuous grain (a usual approach if starting with commercially sawn wood).
This can be attained by employing the outer, under-bark surface of the tree as the bow's backside (convenient for most softwoods), through a detailed process to remove outer growth rings (typically used with yew and osage orange), or by creating or following a cut or split surface that maintains consistent grain patterns (a common method when starting with commercially sawn wood).