The study of fossil pollens from bogs and lake sediments shows that sometimes the percentage of grasses runs quite high. The presence of large amounts of grass pollens has usually been interpreted, often without justification, as proof of prairie invasion. It is certainly necessary to determine the genera of grasses which contributed the pollen before such a conclusion can be made. Keller (5) attempted this in his work on three Indiana bogs. Careful examination and measurements of the grass pollens found and comparison with size frequency of pollens from modern grasses forced him to the conclusion that the predominating pollen present in the bogs was that of Calamagrostis canadensis and not of prairie species. For that reason it has no diagnostic value as an indicator of a xerothermic period in northern Indiana.