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. Mean- 

 while, 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 



