To the above I should add that the 'Lay the Bent' refrain has been discussed at some length here before. Go to http://www.mudcat.org/thread.cfm?threadid=56572#885532 and scroll down to (of course) Malcolm Douglas' post, in which there are links to two previous threads. Malcolm seems to have favoured slightly the sexual motif theory, and also reminded us that the association of the refrain with Child 10 (Two Sisters) is down entirely to Pentangle.

As for the 'Juniper (or Jennifer), Gentle and Rosemary' refrain, associated with one version of Child 1, it's also been collected with 'Two Sisters', 'Babylon' (= 'Bonny Banks of Fordie') and 'The Wife Wrapt in Wether's Skin'. So, one Devil ballad, two murder ballads (one of them supernatural) and one misogynistic comic ballad. Reading anything about the magical power of plants into that refrain, given its disparate associations, would be problematical. Maybe it had no more significance to the people who sang it than 'Fol derol lerol aye day'....