Robert Fortune (1847). “Three Years' Wanderings in the Northern Provinces of China: Including a Visit to the Tea, Silk, and Cotton Countries; with an Account of the Agriculture and Horticulture of the Chinese, New Plants, Etc”, p.141
Ralph Waldo Emerson, Robert Ernest Spiller, Alfred Riggs Ferguson, Wallace E. Williams, Joseph Slater (1987). “The Collected Works of Ralph Waldo Emerson: Representative men: seven lectures”, p.152, Harvard University Press