Slightly longer ago (back in 1882), Francis Child wrote:

"The burden is printed by Gilbert, in the text 'Jennifer gentle and Rosemaree.' He appears to take Jennifer and Rosemaree to be the names of the sisters. As printed under the music, the burden runs, Juniper, Gentle and Rosemary. No doubt, juniper and rosemary, simply, are meant; Gentle might possibly be for gentian."

"The dew (variously glossed as 'dow' and 'dove') flies over the mulberry tree" belongs to that one traditional version only (see above). It has been quoted in many places, frequently without attribution and slightly re-worded, which may give the wrong impression that it occurs in more than one version of that song. The same interleaved refrain (often more garbled) also appears in a good few examples of The Wife Wrapt in Wether's Skin; but only in America. Since there is certainly no supernatural element in that song, nobody seems to have suggested any magical meaning for it in that context.

Chaucer lived long before any of these songs were made. What he may, or may not, have thought is irrelevant. What is relevant is what the people who made these songs, and those who sang them, thought. Until we know what their intention was, any speculation -however interesting- as to the meaning of the refrains they used is just that; speculation.

Child's brief observations on the devil "supplanting" The Elphin Knight were based on the titles alone of two texts, neither of which actually contain any reference to the devil. We don't know whether the titles were provided by the singers or the collectors (the latter was more common at the time), so it can't be taken for granted; "Contemplator's" comment is over-generalised and misleading. The (generally accepted) suggestion that Scarborough Fair derives from The Elphin Knight shouldn't be used as a basis for assuming that the male protagonist is the devil. We have no evidence to support that assumption; and very little to think that the devil belongs in The Elphin Knight at all.

Of course discussion is valid; I haven't suggested otherwise. It's best, though, not to rely entirely on repeating century-old speculation; or anachronistic "neo-pagan" herblore. New, more objective, perspectives are needed if we are to move beyond what has already been suggested long ago.