Pollen and Spores and Their Use 

 in Geology 1 



By Estella B. Leopold and Richard A. Scott 



United States Geological Survey, Denver, Colo. 



INTRODUCTION 



The widespread aerial distribution of plant spores and pollen is 

 made obvious each year by the symptoms of the many hay fever suf- 

 ferers — the pollen count has become as familiar a daily statistic as 

 the relative humidity. Less obvious is the fact that the circulating 

 spores and pollen inevitably must settle out of the air, thus be- 

 coming a part of the continuing accumulation of sediments at the 

 earth's surface. This incorporation of the rain of pollen and/or spores 

 apparently has gone on throughout geologic time since the evolution 

 of spore-bearing plants, although appreciation and utilization of 

 this fact are relatively recent developments in paleontology. 



In the past 25 years there has been increasing use of these plant mi- 

 crofossils in solving scientific problems ranging from the recon- 

 struction of the forest environment of prehistoric man to the correla- 

 tion of Paleozoic coal seams. They are especially valuable in de- 

 termining the changes in climate associated with advances and re- 

 treats of the Pleistocene ice. The study of pollen and spores, formally 

 called palynology, is yielding information increasingly useful in 

 dating sequences of sedimentary rocks and in interpreting past en- 

 vironmental conditions and climatic successions. 



Pollen grains are small (5-200 microns in diameter) reproductive 

 structures representing the male gametophyte in the seed plants. 

 Their transfer to the female reproductive apparatus, a necessary 

 preliminary to fertilization, is effected primarily by wind, water, or 

 by insects. Pollination by wind is necessarily an inefficient process 

 involving a vast supply of pollen grains ; some wind-pollinated plants 

 have as many as 10,000 grains per stamen in flowers with many 

 stamens, and more than 10 million grains may be produced by a 



1 Publication authorized by the Director, U. S. Geological Survey. 



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