1. The Relative Attractiveness to Pollen-Collecting Honeybees of Some Different Pollens
2. ERDTMAN, G. (1969) Handbook of palynology.New York:Hafner Publ. Co.
3. FAEGRI, K.; IVERSON, J. (1964) Textbook of pollen analysis.New York:Hafner Publ. Co.
4. FAEGRI, K.; VAN DER PIJL, L. (1966) The principles of pollination ecology,New York:Pergamon Press