As its title suggests, Arietta is a transcription of a brief didactic composition (entitled Vocalise) of which Martinů later made an arrangement intended for either violin or cello. This would also account for the relative technical simplicity of the piece - for it was composed originally with the possibilities of the human voice in mind - as well as for the total absence of specific violin techniques and double stopping.
Aleš Březina, Martinů: Works for Violin and Piano 2, © 1999 Supraphon Music a.s