Although this early evidence of cross-fertilisation is important, it is during Mahler's extended Wunderhorn phase, in which his Second, Third and Fourth Symphonies were written, that the song and symphony genres are consistently intermingled.
Aínda que esta evidencia inicial de creación cruzada é importante, é durante a fase estendida do Wunderhorn, na que compuxo as súas Segunda, Terceira e Cuarta Sinfonías, cando os xéneros da canción e a sinfonía se mesturaron constantemente.