How does Joseph A. Walker use imagery in The River Niger?

Poetry is an important theme in the play, and John's poem "The River Niger" is clearly a key element of the story, as it lends the play its title. In Act I, John has only begun the poem, which he reads to himself from a scrap of paper in his pocket. Later, he reads a different, completed poem aloud to Ann and Dudley. In the beginning of Act II, John continues to work on "The River Niger," which he reads aloud to himself. Finally, in Act III, after John returns home from a week-long drinking spree, he reads the completed poem, which he has written to Mattie, aloud to an audience that includes the whole family as well as Dudley and Jeff's friends. The poem, which begins, "I am the River Niger—hear my waters!" evokes images of the African roots of African-American people and culture. It suggests that these cultural origins were transported to America with the slave trade, "to the cloudy Mississippi / Over keels of incomprehensible woe" and continue to flow in African-American culture, "Transplanted to Harlem / From the Harlem River Drive." The poem ends with a plea for African Americans not to "deny" their cultural roots: "I am the River Niger! Don't deny me!"