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INTRODUCTION
The absence of a modern general key with detailed descrip-
tions of the species belonging to the Zygnemataceae has greatly
retarded the study of this family. This volume, it is hoped, will
furnish a better manual for the identification of the genera and
species than has been previously available. It seems self-evident
that any studies of life histories, seasonal and cyclic abundance,
and geographic distribution must be based on the accurate naming
of the species considered. In addition to the literature about the
Zygnemataceae, the present descriptions are based on data and
specimens accumulated over a period of thirty-five years.
My interest in the group was originally stimulated by Mr.
Frank S. Collins, who sent me many specimens he had collected,
or received by exchange. These specimens were soon augmented
by exsiccatae from Professors Borge, Nordstedt, Farlow, and
Thaxter. These included numerous type specimens from many
sources, and made possible the revision of earlier descriptions
and the devising of new keys for the separation of species. Meanwhile,
thousands of collections became available for study through
the collecting activities of associates, graduate students, and myself
throughout the eastern half of the United States, and from
Ontario to Cape Breton Island. From Finland, Latvia, South
Africa, Central and South America, Puerto Rico, China, India,
Japan, and the Philippine Islands, several hundred additional col-
lections have been received from correspondents. During the
most active period of the study of these collections, I had the
assistance of Professors L. H. Tiffany and C. E. Taft, who checked
literally scores of the determinations and verified numerous de-
scriptions of new species. To them I am most grateful for their
help, and for the feeling of satisfaction that the new descriptions,
particularly of spore walls, have been verified by at least one
other pair of eyes.
Whether one accepts all of the genera, or all of the species, as
valid or not, they seemed to differ in enough particulars to war-
rant their separation at the time they were studied. Some of the
species described during the early history of the group have been