The haunting (some say spooky) clarinet of "Clarinut"
Late on the evening of January 3, 1924, George Gershwin and Buddy De Sylva were playing billiards in the Ambassador Billiard Parlor at Broadway and 52nd Street in Manhattan. His brother, Ira, was reading the January 4 edition of the New York Tribune. An article entitled "What Is American Music?" about a Paul Whiteman concert caught his attention, in which the final paragraph claimed that "George Gershwin is at work on a jazz concerto, Irving Berlin is writing a syncopated tone poem, and Victor Herbert is working on an American suite". In a phone call to Whiteman next morning, Gershwin was told that Whiteman's rival, Vincent Lopez, was planning to steal the idea of his experimental concert and there was no time to lose. Gershwin was persuaded to compose the piece.
On a train journey to Boston, ideas for Rhapsody in Blue came to mind. A quote of Gershwin: "It was on the train, with its steely rhythms, its rattly-bang, that is so often so stimulating to a composer - I frequently hear music in the very heart of the noise... And there I suddenly heard, and even saw on paper - the complete construction of the Rhapsody, from beginning to end. No new themes came to me, but I worked on the thematic material already in my mind and tried to conceive the composition as a whole. I heard it as a sort of musical kaleidoscope of America, of our vast melting pot, of our unduplicated national pep, of our blues, our metropolitan madness. By the time I reached Boston I had a definite plot of the piece, as distinguished from its actual substance".
Upon returning to his New York apartment on January 7, he began composing the original manuscript for two pianos. The piece was titled "American Rhapsody" during composition. The title "Rhapsody in Blue" was suggested by Ira Gershwin after his visit to a gallery exhibition of James McNeill Whistler paintings. After a few weeks, Gershwin finished his composition and passed the score to Whiteman's arranger, Ferde Grofé, who orchestrated the piece, finishing it on February 4, only eight days before the scheduled premiere. Due to the rushed circumstances and other commitments, Gershwin reportedly had no time to write out the piano solo passages, which he played from memory (and, being the great improviser that he was, probably embellished considerably). Gershwin's understanding with Whiteman was that he would nod when his solos were over and the next orchestral portion was to begin.
Rhapsody in Blue premiered in a matinee concert on February 12, 1924, held by Paul Whiteman and his band, Palais Royal Orchestra, entitled “An Experiment in Modern Music”, in Aeolian Hall in New York City. The next day, New York Times critic Olin Downes wrote "The audience packed a house that could have been sold out at twice the size". Billed as an educational event, the "Experiment In Modern Music" concert was organized by Whiteman to demonstrate that the relatively new form of music called jazz deserved to be regarded as a serious and sophisticated art form. The program featured segments intended to make this case - segments with titles like "Contrast: Legitimate Scoring vs. Jazzing." After 24 of these numbers, the house grew restless, and many of those in attendance lost interest and had left the hall by the time George Gershwin, the young composer, took his place at the piano to perform Rhapsody in Blue.
What happened next brought those in the aisles back to their seats and recaptured the entire house. Ross Gorman's unexpected and unforgettable "outrageous" opening clarinet glissando electrified the house!
Listen to Gorman's glissando and beginning
Gershwin had originally written the opening of Rhapsody in Blue as a clarinet trill followed by a 17-note legato scale in 64th notes. The glissando came into being during a rehearsal as a joke on Gershwin. Ross Gorman, Whiteman's virtuoso clarinetist, played the opening with a pronounced glissando, adding what he considered a humorous touch to the passage. Reacting favorably to Gorman’s whimsy, Gershwin asked him to perform the opening measure that way at the concert and to add as much of a ‘wail’ as possible. Gorman experimented before the concert with various reeds until he found the one that gave him the most 'wailing' sound. The opening glissando heard at the concert has never been played as well by anyone else; Gorman played the glissando from F# below the staff all the way to C above the staff (as transposed for the Bb clarinet). Gorman's clarinet also had its own personality throughout the piece, with a unique "laughing" sound in certain passages.
Rhapsody in Blue, with its audacity and intensity, kept the attention of the audience for the entire performance, even through places in the score where Gershwin left several piano solos blank and penciled in a direction for Whiteman to "wait for nod". After its climactic finale, there was tumultuous applause.  For Gershwin, it was a turning point, the beginning of a career that would make him the most widely performed American composer of the 20th century. It was also a turning point for modern music. By "making a lady out of jazz", Rhapsody in Blue set in motion a new trend in music; composers all over the world began composing serious works in the jazz genre.
(Material gleaned from information on the internet)