No provisions of sections 951 to 957 shall be construed to prevent a grower or shipper of potatoes from selling or delivering the same within the State unpacked, or selling his crop in bulk, or any part thereof, to a packer for grading, packing or storage within the State; nor shall any provision of said sections prevent any person from manufacturing the same into any by-product, or from selling the same unpacked to any person actually engaged in the operation of a commercial by-products factory for the sole and express purpose of being used within the State in the manufacture of a by-product.   [PL 1965, c. 219, §5 (AMD).]