"Michigan's Upper Peninsula provides excellent habitats for the study of the algal flora. It was this fact, plus a rather recent acquisition of knowledge concerning the algae, that summoned the writer to embark on a nine month study of the desmids from two small bodies of water near Marquette, Michigan. Part I of this study, dealing with desmid periodicity, is an attempt to determine the abundance of certain genera of desmids during various intervals (usually weekly). There are several avenues open to the investigator who wishes to determine the abundance of algal flora, however, when the field is narrowed and attempts are made to determine the number of genera in a mixed medium there seems to be no alternative other than to count the actual specimens. or the purposes of this investigation, seven genera were selected primarily on the basis of the writer's familiarity with the genera at the beginning of the project. Part II is purely taxonomic and is an attempt to classify as many species as possible within the areas selected."--Introduction.