FOREWORD. 
For many years the only available keys to the Freshwater 
Algz of North America were those published by Francis Wolle 
about 1887. These were in larger part transcriptions of European 
descriptions often based on a single collection. Moreover, at 
that time it was a common practice to name specimens on the 
basis of vegetative characters or of immature reproductive 
structures. Consequently many of the records are erroneous 
and many others are questionable. 
In 1909 Frank S. Collins published a monograph of the 
Green Algze of North America. He not only added many 
species and records to the North American algal flora, but also 
corrected many of the previous errors in nomenclature and in 
the locality records, and brought the taxonomy of the green 
algze in America into harmony with the best usage in Europe. 
Collins’ keys stimulated a wide interest in the green alge in 
this country, and led to the publication of many local lists and 
papers describing new species. 
In the determination of algae, however, descriptions without 
plates are frequently difficult to interpret, and the greatest 
need of American students today is a series of illustrated 
monographs of the various families and orders. 
The world wide distribution of many of the freshwater 
alge, and the possibility that a species described from Australia 
may be found in Ohio has made it desirable that the monographs 
should attempt to cover all the described species. Too often 
the literature of a group is widely scattered and many of the 
papers are in obscure journals quite inaccessible to the average 
student. 
In 1900 Karl E. Hirn of Helsingfors, Finland, published in 
Latin and German a monograph of the Oedogoniacee that has 
been a model and inspiration for all algologists, but this volume 
and its supplement are now difficult to secure. Moreover 
many new species have been described and the descriptions by 
Hirn in many cases have been emended. It has seemed there- 
fore very desirable to publish descriptions and keys to all 
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