The first is a reference to ‘chasing the maiden’. Apparently a bride-to-be was chased by her jealous unmarried friends and when caught was stripped and thrown to the ground and whipped with ‘apple switches’ on her bare bottom to make her fruitful. ‘Nor was this done in jest and a maiden could expect more than cats scratches upon her posteriors afterwards. Also it must be said, she was scarce likely to behold a pew come Sunday.’
Another was an alleged New England custom dating to the 17th century. Before her nuptials it was said that a maiden would be taken into the orchard (another pagan fertility connection perhaps) and made to bare her bottom and bend over a fence rail. Then she was whipped across the bare bottom with a rod or a switch.
This was done slowly and with force. The more strokes she could accept before ‘begging off’ was supposed to indicate how many years of happiness she would have when married.
A variant on this was the more strokes the more healthy children.