Preface. 



Since the publication of Schimpers Synopsis muscorum euro- 

 pseorum (1876) and Manual of the mosses of N. America by 

 Lesquereux and James (1884), the bryology is enriched by many 

 new species. Also several very important bryological manuals, 

 viz. by Boulay, Braithwaite, Husnot and Limpricht, have contri- 

 contributed to a more complete knowledge of the mosses. 



The present treatise is an essay to revise and compare all 

 hitherto known species and subspecies of Bi-yinese, found in Eu- 

 rope and N. America. Excluded species are regarded as varieties 

 or not sufficiently known. 



I believe that the greatest importance is to attache to the natural 

 affinity of such species as could be joined to common types 

 (subgenera or groups). Affinity is not to be defined through a 

 few artificial characters, stated »a priori*. It needs therefore 

 to select characters, peculiar and constant to each genus. Some 

 characters are in some genera variable, but in others constant. 



I have therefore not described selected specimens in all their 

 parts but generally omitted such characters, as evidently 

 are too variable. When some species are critical or hitherto 

 not well-known, I have tried to propose all their necessary di- 

 stinctive characters. 



To facilitate the determination of sterile specimens, so often 

 occurring, I have accurately described the areolation of the lea- 

 ves and the common habit of the vegetals. 



My descriptions are not transscribed from other authors but 

 based on my own microscopical researches and studies in nature. 

 I have therefore in Europe visited northern and southern districts 

 and their different regions up to the glaciers and the perennial 

 snow, also augmented my collections through contributions by 

 many correspondents. The geographic distribution and the sta- 

 tions of N. American mosses are accurately observed principally 

 by Prof. J. Macoun, D:r J. Roell and the Rev:d A. C. Waghorne, 

 also (in Greenland) by Prof. S. Berggren. 



