1. Carlson, P.S.: Induction and isolation of auxotrophic mutants in somatic cultures of Nicotiana tabacum. Science 168, 487?489 (1970)
2. Constabel, F., Kao, K.N.: Agglutination and fusion of plant protoplasts by polyethylene glycol. Canad. J. Bot. 52, 1603?1606 (1974)
3. Gamborg, O.L.: Callus and cell culture. In: Plant tissue culture methods, pp. 1?10. Gamborg, O.L., Wetter, L.R., eds. Saskatoon, Sask.: Nat. Res. Counc. Canada, 1975
4. Gamborg, O.L., Miller, R.A., Ojima, K.: Nutrient requirements of suspension cultures of soybean root cells. Exp. Cell Res. 50, 151?155 (1968)
5. Howard, A., Pelc, S.R.: Synthesis of deoxyribonucleic acid in normal and irradiated cells and its relation to chromosome breakage. Heredity (Lond) 6, Suppl., 261?273 (1953)