distinctive feature compared with other plainchant repertories is a significantly higher amount of stepwise motion, which gives Ambrosian melodies a smoother, almost undulating feel. In manuscripts with musical notation, the neume called the climacus dominates, contributing to the stepwise motion. More ornamental neumes such as the quilisma are nearly absent from the notated scores, although it is unclear whether this reflects actual performance practice, or is simply a consequence of the relatively late musical transcription. The Gregorian system of modes does not apply to Ambrosian chant. Although there are no b-flats indicated in the musical notation, it seems likely that they were understood, based on Guido d'Arezzo's description of the "more perdulcis Ambrosii." Nearly all of the texts used in Ambrosian chant are biblical prose, not metrical poetry, despite Ambrose having introduced Eastern hymnody to the West. Ambrosian chant serves two main functions in the Ambrosian liturgy: to provide music for the chanting of the Psalms in the monastic Offices, and to cover various actions in the celebration of the Mass. Chants of the Office The Office chants of the Ambrosian repertoire are still largely unresearched, so only preliminary evaluations have been made. The minor hours have little of musical interest: some hymns, and the simplest of reciting tones only. The main chants of the Office are those of Matins, Vespers and the Vigils. The Psalms are sung at Matins and Vespers in a rotating schedule so that all 150 Psalms are chanted every two weeks. The Psalms are each sung to a psalm tone, with a simple antiphon between each verse. The system of psalm tones in Ambrosian chant differs in several respects from the Gregorian system of psalm tones. In the Gregorian system, psalm tones are based on the mode of the antiphon. Ambrosian chants, including psalm antiphons, do not conform to the Gregorian system of modes. Each Ambrosian psalm antiphon belongs to one of four different series depending on its final pitch. Within each series, there are several possible psalm tones corresponding to the predominant pitch of the antiphon, which may or may not correspond to the "dominant" pitch of Gregorian modes. Finally, each psalm tone is given a cadential formula that lets the tone segue smoothly back into the antiphon. This system results in a much larger number of possible psalm tones in Ambrosian chant than exists in Gregorian chant. Structurally, psalm tones in Ambrosian chant