1. Erdtman, G. 1952. Pollen morphology and Plant Tax-onomy. I. Angiosperms. — Almqvist & Wiksell, Stockholm.
2. Erdtman, G. 1969. Handbook of Palynology. — Hafner Publishing Co., New York.
3. Rehder, A. 1940. Manual of Cultivated Trees and Shrubs. — MacMillan Co., New York.
4. Sargent, C. S. 1949. Manual of the Trees of North America. — Dover Publications, New York.
5. Wodehouse, R. P. 1935. Pollen Grains. — McGraw-Hill, New York.