John Hallberg, in a discussion on Farcebook today, helped me find an answer to a question that has been bothering me for two years or more.
Child Ballad #1 is called Riddles Wisely Expounded. That's the story of the song -- riddles asked and answered -- although both words and music have changed many times since the 1400s. One of the versions I know and perform is called Lay The Bent To The Bonnie Broom. There are 20 or so two line verses with dual refrains "lay the bent to the bonnie broom" and "And you'll beguile a lady soon". Like this:
There were three sisters in the North Lay the bent to the bonnie broom And they live'd in their Mother's house And you'll beguile a lady soon
There came a knight by middle day Lay the bent to the bonnie broom Asking for a place to stay And you'll beguile a lady soon.
Problem is/was that I'd been saying "lay the bend to the bonnie broom" and no one had any real idea what the heck that meant!
It turns out that Bent or Bentgrass is wirey type of rush, and like Broom it was one of the "sacred plants" to the Druids. Combining pagan and early Christian practices, laying the bent on the bonnie broom -- making the sign of the Cross from a bundle of bent crossing a bundle of broom -- made a potent symbol that would keep the Devil at bay. Or in the context of the song, if the visiting knight could make a cross from bent and broom it would prove he was not the Devil in disguise -- and so be fair game for the maidens to seduce him into marrying one of them.