1. Abbe, C. 1905. A first report on the relations between climates and crops. U.S. Govern ment Printing Office, Washington, D.C. Bulletin 36, W.B. No. 342, 386 pp.
2. Abrami, G. 1972. Optimum mean temperature for plant growth calculated by a new method of summation.Ecology53 (5), 893–900.
3. Arnold, C. Y. 1959. The determination and significance of the base in a linear heat unit system.Proc. Am. Soc. Hort. Sci. 74, 430–445.
4. Arzt, T., and W. Ludwig. 1950. Alte Probleme der Phänologie in neuer Beleuchtung.Met. Rdsch. 2, 450–459.
5. Balvoll, G., and A. H. Bremer. 1965. Varmesum og planteavl i samband med vekst og utvikling av ymse grønsakvokstrar. (The heat-unit system and plant production in connection with growth and development of different vegetables).Meldinger Norges Landbrukshøgskole44, 1–18.