INTRODUCTION. 



PREVIOUS PUBLICATIONS. 



In the summer of 1886 I published for free distribution a 

 key to the genera of mosses recognized in the Manual of 

 Lesquereux and James. A large edition of that key was 

 soon exhausted, and I have been frequently assured that it 

 proved of real service to students of mosses. Although 

 much misgiving was felt as to its accuracy very few 

 changes have been found necessary, and it is now presented 

 for the third time substantially as it was at the first, ex- 

 cept for the changes involved in its extension to include 

 the sub -genera of Hypnum, most of which, as given in the 

 Manual referred to, are certainly of generic rank. 



Encouraged by the approval of the key to genera, in 

 May, 1890, I published keys to the species of North Ameri- 

 can mosses recognized by Lesquereux and James. These 

 keys were printed in the eighth volume of the Transac 

 tions of the Wisconsin Academy of Sciences, Arts and Let- 

 ters, and a considerable edition of separates was also struck 

 off. In those keys I included the comparatively small 

 number of new species which had been described since the 

 the issue of the Manual. The work made no pretensions 

 to a critical study of North American mosses, but was de- 

 signed only as a convenience for students. The new 

 edition here presented is meant to serve the same purpose 

 more fully. 



THE NEW EDITION. 



Three reasons have induced me to prepare a new edition. 

 (1) The separate edition printed in 1890 was exhausted sev- 



