1Mix together mulberries, rhubarb, sugar, and flour.
2Pour into unbaked 9 inch pie shell. Dot filling with butter or margarine, and add top crust.
3Bake at 400 degrees F (205 degrees C) for 15 minutes. Reduce oven temperature to 350 degrees F (175 degrees C). Bake until pie is done, about 30 minutes.