Legend has it that in ancient times, there was a pharmacologist, a minister of Huangdi, renowned for his expertise in materia medica. Tao Hong-jing of the Liang Dynasty, in the preface to Bencao Jing Jizhu, emphasized: "As for the medicinal properties, they should be understood through mutual recognition; otherwise, how could one gain knowledge? As for Tong Lei, his works are recorded in the scrolls, and this book should be of the same category as Suwen." "There is also Tongjun's Herbal Collection, which describes the shapes and colors of the flowers and leaves; and Yaodui in four volumes, discussing the mutual recognition of adjuvants and messengers."