Some links relating to the American Acorn Mystery:
NYC Garden explains what has happened to the missing acorns.
Brooklynometry has a beautiful photograph of some existing Prospect Park acorns.
Then there's this tale, by Jon Evans, which predates and predicts our present Acorn Crisis.
I think they lie strewn between the Tigris and the Euphrates. Gone to graveyards every one.
Where do you think they are?