1. Arnold, J. P. 1911. Origin and history of beer and brewing from prehistoric times to the beginning of brewing science and technology: a critical essay. Alumni Association of the Wall-Henius Institute of Fermentology, Chicago.
2. de Candolle, A. 1964. Origin of cultivated plants. Haffner, New York. Reprint of a work first published, asOrigine des plantes cultivées, by G. Bail-liére et cie., Paris, in 1883.
3. Edwardson, J. R. 1952. Hops—their botany, history, production, and utilization. Economic Botany 6:160–175.
4. Gross, E. 1900. Hops: in their botanical, agricultural and technical aspect and as an article of commerce. Translated by Charles Salter. Scott, Greenwood & Co., London.
5. Hegi, G. 1936. Illustrierte Flora von Mitteleuropa. 2nd ed. Lehmann, Munchen.