Chalk it up to the privileges and pressures of designing for eternity (“Forever” beats first-class any day) or the security that comes with a future of free Saturdays, but the United States Postal Service is on a roll when it comes to fetching stamps. The agency is following up its Armory Show centennial “Modern Art in America” stamps with a fresh take on flowers, a perpetual crowd-pleaser for philatelists and Johnnies-come-philately alike. Behold “Vintage Seed Packets,” a bouquet of ten self-adhesive blossoms sourced from antique seed packets (pictured at right, printed between 1910 to 1920) and cropped to highlight the detail of flowers from asters to zinnias. Each flower is identified in bold capital letters, lest you mistake a calendula for a phlox. USPS art director Antonio Alcalé is to thank for the design of the stamp booklet, which debuts next Friday, April 5.