The song must be based on the O Henry short story "The Last Leaf," about a girl who was convinced she would die when the last leaf fell from a tree outside the window near her sick bed. When the leaf didn't drop (because it had been tied on), she passed the crisis of her illness and recovered. The story, along with several other O Henry tales, was made into a movie in the '40s or '50s, I think. Among the other stories in the film were "The Ransom of Red Chief" and "The Gift of the Magi." --seed