42 BEITISH MOSSES. 



I have hitherto spoken of the peristome as consisting 

 of one girdle of teeth ; often it is double as in the 

 great genera Hypnum and Bryum, and then the 

 teeth often reach the number of sixty-four. In one 

 foreign genus (Dawsonia) there are as many as four circles 

 of teeth. 



The accompanying Fig. 26 is a diagram intended to 

 assist the reader in gaining a general notion of the 

 structure of the several parts of a capsule with a double 

 peristome : it is a diagram only of a section of an ideal 

 capsule, and not a picture or representation of any 

 existing capsule. The reader who will carefully inspect 

 it will learn what to look for when he first holds a 

 capsule in his hands, and may get some assistance as 

 regards the technical language of bryology. He will 

 see the calyptra, or veil (caZ.), the remains of the ori- 

 ginal archegone ; he will see the operculum, or lid (oper), 

 severed from the capsule itself ; he will observe the double 

 peristome (i.p. and o.p.), the outer teeth consisting of a pro- 

 longation of the outer coat of the capsule, the inner teeth 

 arising in like manner from the wall of the inner sack or 

 spore case, or sporangium (sp.) ; he will observe an interspace 

 between these two sacks filled with cellular tissue ; he will 

 observe in the interior of the sporangium the cells which 

 become spores with the maturity of the growth ; and in 

 the middle of the diagram he will notice the columella 

 or column. At the base of the capsule he will see 

 the region (op-) which, when swollen or enlarged, gives 

 rise to the apophyse. All these parts are subject to 

 a great range of variation, but this diagram may never- 



