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The song poem sub-industry was when amateur poets and would-be songwriters would send in their poems/lyrics to be set to music by professionals, in hopes of becoming the next Johnny Mercer.
A few years ago PBS ran a very interesting documentary on the phenomenon titled Off The Charts :
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The most fascinating figure in the song poem world was a multi-talented producer-arranger-musician-singer named Rodd Keith, who I hope to discuss in a future post. For now, here's one of the more intriguing examples of the form, a touchingly romantic piece called "Green Fingernails":