"Trun" is in my copy of "The American Songbag". There is an introductory note that says "the word "trun" means "threw" or "throwed"; it rhymes with fun". It also says that the fourth/last verse (the one with "trun") was contributed by "philosophers at the extreme left in the labor movement and in modernist art in Chicago". There are some other small differences from the link to Art Thieme's version, provided by Stewart.