1. Åkerman, Å., and J. MacKey, 1948. The breeding of self-fertilized plants by crossing. In: Åkerman, Å.
et al, Svalöf 1886–1946. p. 46–71.
2. Allard, R. W., 1960. Principles of Plant Breeding. John Wiley & Sons, N. Y. 485 p.
3. Bal, B. S., C. A.Suneson, and R. T.Ramage, 1959. Genetic shift during 30 generations of natural selection in barley. Agron. Jour. 51: 555–557.
4. Cook, O. F., 1932. Cotton improvement through type selection, with special reference to the Acala variety. USDA Tech. Bull. 302. 62 p.
5. Coons, G. H., 1936. Improvement of the sugar beet. USDA Yearbook. 625–656.