How did Show Boat help integrate songs with a musical's plot?

The 1927 production of Show Boat, with music by Jerome Kern and book and lyrics by Oscar Hammerstein II, was a landmark in the evolution of the musical genre. It is recognized as the first musical to provide a cohesive plot and initiate the use of music that was integral to the narrative.12

Unlike earlier musical comedies that relied on a series of songs and musical numbers, Show Boat drew its serious plot from a literary source—Edna Ferber’s novel of the same name—and incorporated music that served the story. By addressing serious American themes such as racial prejudice and utilizing music derived from folk melodies and spirituals, the production inaugurated the serious musical play in the United States. This approach of integrating songs into a cohesive whole set a standard for the genre, a practice that was fully realized in later works during the 1940s.132