This chapter shall take effect as follows: As to agricultural seeds, and the importation of vegetable seeds, on the one hundred and eightieth day after ; as to vegetable seeds in interstate commerce, one year after ; and as to sections 1591 to 1593 of this title, on .August 9, 19391939-08-09August 9, 19391939-08-09August 9, 19391939-08-09