44 HANDBOOK OF BRITISH MOSSES. 



natural arrangement the Phascoid Mosses must be distributed 

 amongst those which are Stegocarpous, the distribution is 

 not tenable. 



Generic characters depend upon the structure and situation 

 of the fruit; but though the differences of the peristome 

 afford in many cases admirable characters, in others great 

 latitude must be taken in their use. Where natural groups 

 are sought for, the same genus will sometimes comprise species 

 with a single or double peristome, or in which it is altogether 

 wanting. The old genus Gymnostomum is now properly dis- 

 tributed amongst widely distant groups. 



The calyptra occasionally affords good characters, but it is 

 sometimes deceptive. The vaginula is often of great import- 

 ance, but it is not so obvious a source of distinction as parts 

 which are more exposed to view. The comparative length of 

 the lid is often employed as a mark of distinction by Con- 

 tinental authors, but seldom with much advantage. 



The male inflorescence rarely affords good generic charac- 

 ters, though it sometimes comes in aid of others, as in Bryum 

 and Mnium. The reticulation of the leaves is often indicative 

 of natural affinity, and occasionally is available for generic 

 distinctions ; but the refinements of Continental Bryologists, 

 especially in the genus Hypnum, are not calculated for prac- 

 tical purposes ; and though their groups are generally natural, 

 it is often impossible to reconcile them with the proposed dis- 

 tinctions. 



The arrangement of Dr. Montagne, in Orbigny's Diction- 

 ary, as regards the Natural Orders into which the tribes are 

 divisible, though laying no claim to originality, appears to be 

 one of the most convenient, and was followed in the ' Intro- 

 duction to Cryptogamic Botany,' and, with few exceptions, is 

 the same with that adopted here. 



