d'artifice (1908/9). These works clearly reveal the influence of Rimsky-Korsakov, but as Richard Taruskin has shown, they also reveal Stravinsky's knowledge of music by Glazunov, Taneyev, Tchaikovsky, Wagner, Dvořák, and Debussy, among others. The Firebird looked backward to Rimsky-Korsakov not only in its orchestration, but also in its overall structure, harmonic organization, and melodic content. According to Taruskin, Stravinsky's second ballet for the Ballet Russes, Petrushka, is where "Stravinsky at last became Stravinsky," referring to his "process of self discovery." The Russian influence can be seen in the use of a number of Russian folk tunes in addition to two waltzes by Viennese composer Joseph Lanner and a French music hall tune (La Jambe en bois or The Wooden Leg). Neoclassical period (–1954) Apollon musagète (1928), Perséphone (1933), and Orpheus (1947) exemplify not only Stravinsky's return to the music of the Classical period but also his exploration of themes from the ancient Classical world, such as Greek mythology. The first movement of his Octet (1923) uses the sonata form, showing his return to older structural styles. Important works in this period include the Concerto for Piano and Wind Instruments (1924), the Serenade in A (1925), and Symphony of Psalms (1930). Serial period (1954–1968) In the 1950s, Stravinsky began using serial compositional techniques such as dodecaphony, the twelve-tone technique originally devised by Schoenberg. He first experimented with non-twelve-tone serial techniques in small-scale vocal and chamber works such as the Cantata (1952), the Septet (1953) and Three Songs from Shakespeare (1953). The first of his compositions fully based on such techniques was In Memoriam Dylan Thomas (1954). Agon (1954–57) was the first of his works to include a twelve-tone series and the second movement from Canticum Sacrum (1956) was the first piece to contain a movement entirely based on a tone row. Stravinsky expanded his use of dodecaphony in works such as Threni (1958) and A Sermon, a Narrative and a Prayer (1961), which are based on biblical texts, and The Flood (1962), which mixes brief biblical texts from the Book of Genesis with passages from the York and Chester Mystery Plays. Innovation and influence Stravinsky has been called "one of music's truly epochal innovators". The most important aspect of Stravinsky's work, aside from his technical innovations (including in rhythm and harmony), is the "changing face" of his compositional style while always "retaining a distinctive, essential identity". Stravinsky's use of motivic development