The centennial of Siskind’s birth is the occasion for a number of exhibitions of his photographs, from his early (1932-40) “Harlem Document” series at the Studio Museum to a smart sampling of images from throughout his career at the Whitney, but the show at Robert Mann (which represents the artist’s foundation) offers the largest, broadest, and most definitive selection. Siskind’s genius was to take the self-consciously arty still life—long a staple of both highbrow aesthetes and camera-club amateurs—and toughen it up. Inspired by his abstract expressionist peers like Franz Kline, Willem de Kooning, and Barnett Newman (whose work hangs alongside Siskind’s at a great little show at Andrea Rosen), he devised a photographic equivalent to their rough, gestural spontaneity in closely cropped pictures of peeling plaster, torn paper, graffiti, rocks, and tar. His feel for the sensuous tactility of this found material is balanced by an innate formal elegance. The results are perfectly poised, utterly timeless examples of photography at its most artful and accessible.