Volume 13 of the illustrations series is devoted to 33 plant families, a number of which are of horticultural or agricultural importance or are otherwise distinctive: Violaceae, with its white, purple, and yellow violets; Passifloraceae, the passion flower family; Caricaceae, of which the genus Carica furnishes us with the papaya fruit; Begoniaceae, with Begonia, noted for its ornamental flowers and foliage; Cactaceae, featuring the Cactus genus; Thymelaeaceae, including the ornamental shrubs Daphne, and Edgeworthia used for the manufacture of paper and medicines; Trapaceae, the water chestnuts; Nyssaceae, containing the genus Camptotheca, source of the anticancer drug camptothecin, and Davidia, the dove tree, which naturally occurs only in China; Onagraceae, including evening primrose and Epilobium or willowherb; and Araliaceae, containing the ivies as well as Panax or ginseng.