Date of this Version
This paper is intended chiefly to assist in the identification of common and significant pollen found embalmed in bog deposits in north-central United States. Before proceeding with the actual key and description, a brief explanation seems to be in order.
For a number of years European botanists have been counting the various species of pollen found at different levels in bogs. Such statistics have been used to trace the course of plant succession and the climatic changes of which it is held to be the expression. Stark (9) has prepared a concise summary on the subject up to about 1924; Erdtman (3) has arranged the literature preceding 1927; while Fuller (5) has twice noted for American students the general results in this field. Work continues actively in Europe and is under way in the United States.