Middle English Verbal Prefix i-

Middle English appears to have had a prefix i- which could appear before
verbs. Some well known examples of this prefix in action are

"Adam lay ibounden,
Bounden in a bond..."

"Miri it is while sommer ilast with flugeles song..."

and most famously of all

"Summer is icumen in,
Lhude sing cuckoo!"

What I can't discern from these examples is what the morpheme actually
means. Given that all the examples above are from songs, I do have the (to
my mind) somewhat unsatisfactory theory that it may be a poetic flourish.
Can anyone shed more light on it?

Pete

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