134 
scribed rather than to complicate the matter by making anew 
species of every doubtful specimen at hand. Doubtless a more 
complete knowledge of our moss-flora will show that many forms 
described as varieties will prove to be good species. 
The keys are entirely new and have been made with special 
reference to their use by amateurs. Gametophyte characters have 
been used in preference to sporophyte characters wherever possi- 
ble, in order to facilitate the identification of sterile specimens. 
Special care has been taken to correlate the descriptions so that 
any character of two closely related species can be easily compared. 
Measurements, both comparative and absolute, have been given in 
order to facilitate such comparisons. 
The absence of many published varieties will be noticed and 
probably criticized. The extreme multiplication of varieties, so 
much in vogue with the Germans, seems to the author to be con- 
fusing and valueless. Only well marked varieties, with characters 
easily recognizable, have been included. Often these would seem 
to be good species except for the many intermediate forms. In 
other cases more material will probably give characters sufficient 
to raise the varieties to specific rank. 
