Dictyota dichotoma Alga

History's first photo book, in Prussian blue. Dictyota dichotoma young and in fruit, cyanotype photogram from Photographs of British Algae (part XI, 1843-1853). Laid directly on sensitised paper, the alga draws its white shadow on blue: an almost abstract gesture, a century before abstraction.

Plate from the virtual exhibition Wondrous Flora (Trace Museum, 1705-1887).