The Secretary of Agriculture of the Department of Agriculture of this Commonwealth is hereby authorized and empowered, after investigation, to establish and promulgate official standards of quality for grading and classifying potatoes, apples and peaches and to change any of them from time to time. The official standards so established and promulgated shall be the same in their requirements as the requirements of the official standards for corresponding grades of potatoes, apples or peaches as promulgated from time to time by the Secretary of Agriculture of the United States, which standards are commonly known as “United States Grades.”

From and after the establishment of specific grades or standards of quality as hereinbefore provided potatoes, apples and peaches in closed packages shall not be shipped for sale or thereafter sold or exposed for sale except by the grades or standards so established: Provided, however, That potatoes, apples and peaches not graded and classified as to quality may be shipped for sale or sold exposed for sale as “unclassified,” if so marked in a conspicuous manner in accordance with rules to be adopted by the Secretary of Agriculture of the Department of Agriculture of this Commonwealth as hereinafter provided.