A mechanism for enveloping a large round bale with a wrap material such as plastic sheet or net includes a housing for holding a supply roll of such material. The mechanism is mounted to the rear of a bale discharge gate. The housing is substantially enclosed except for an open front which is closed by a panel carried by the gate. The housing is vertically pivotally mounted for swinging away from the gate to a lowered position disposing its open front so that it faces rearwardly for reception of a supply roll of wrap material. A spring-loaded U-shaped structure is provided on the housing for biasing the material toward a lower front corner defined at the juncture of a plane containing a bottom wall of the housing and the panel.