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{Gutjahr, C.C.M.: Carbonization Measurements of Pollen-Grains and Spores and Their Application.  Leidse Geol. Meded. 38:1-10,13-29 (1966)
 

Kremp, Gerhard O. W. - Morphologic Encyclopedia of Palynology: An international collection of definitions and illustrations of spores and pollen.  The Universtiy of Arizona Press: Tucson. 1968.

Tschudy, Robert H.; Scott, Richard A. Aspects of Palynology. Wiley-Interscience: Toronto. 1969.