The Chaucer Review: An Indexed Bibliography (Vols. 1-30)

Maltman, Sister Nicholas, O. P. "The Divine Granary or the End of the Prioress's 'Greyn.'" 17 (1982): 163-70.
In her tale the Prioress refers to the Sarum breviary and the Mass of the Holy Innocents. In the response to the Sarum liturgy, the grain represents St. Thomas a Becket's martyrdom, and specifically the soul "winnowed" (165) from the body. Chaucer chose the grain for its connection with the Holy Innocents and St. Thomas, both of whom are associated with martyrdom. The grain on the boy's tongue physically represents his soul.