classical pastoral
             tradition; such as the pipe and the hollow reed, the sweet
             lot of the shepherd and the pleasant sounds of nature.
             Blake uses a fairly clever conceit in the last stanza to
             have the Piper manufacture a 'rural pen' out of a hollow
             reed, rather then to pluck one from a bird, for it is a
             routine pastoral fact that pipes are made of hollow reeds;
             the pen, then, is thus a transformed pipe.
             ...