The term "containers" means cloth, plastic, paper, or fiber sacks (such as are customarily used in the shipment of potatoes), cartons, barrels, boxes, crates, hampers, or baskets. Cloth or fiber sacks in which potatoes not exempt under the provisions of this act are packed for shipment, shall be new or recleaned, bright, undamaged sacks. Provided, however, that on and after September 1, 1949, no container known as a mugged bag can be used on any grade or grades of potatoes as defined in this act. The term "mugged bag" means any bag, after such bag has been filled and the top thereof closed or secured, which is not fully closed at the top and which leaves the mouth thereof partially open so that the lips of the bag are not drawn closely together.