Chant melodies inspired instrumental works as well as vocal. Check out the chant melody below (the “Haec dies” for Easter Day) and then listen to how Widor used it in his magnificent Symphonie Romane (performed in the very building for which it was written).
Full Symphony: http://www.youtube.com/view_play_list?p=97877A380326412E Widor's Tenth and finale Organ Symphony, performed on the great gallery organ of the ...