Preface. 
Since the publication of Schimpers Synopsis muscorum euro- 
peorum (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 Bryinez, 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. | 
