THE MOSS TRIBE. 277 



in distinguishing the genera. Let it, therefore, engage 

 our attention the first. No species can be more common 

 than Wall Tortula (Tortula muralis), dark tufts of 

 which are found every where upon the north side of 

 walls, growing out of the mortar. The theca of this 

 plant wears a little cap, not very unlike that of the 

 Norman peasant women (^Jig. 2. a.), with its high 

 peak and long lappets ; this part is called a calyp- 

 TRA ; when young it was rolled round the theca, so 

 as completely to cover it over like an extinguisher, 

 hut when the stalk of the theca lengthened, the ca- 

 lyptra was torn away from its support, and carried up 

 upon the tip. After a certain time, the calyptra drops 

 off; and, at that time, the theca is in the best state 

 for examination. You will find it terminated by a 

 conical lid (j%. 3. a.), or operculum, which is thrown 

 off when the spores, or reproductive parts, are fit to 

 be dispersed (Jig. 4. h.). When the lid has been thus 

 spontaneously thrown off, a new and peculiar set of 

 parts come in view ; you will find that the lid cover- 

 ed a kind of tuft of twisted hairs, which at first look 

 as if they stopped up the mouth of the theca. But, 

 if you cut a theca perpendicularly from the bottom to 

 the top, you will learn from the sectional view that 

 you will then obtain of the parts, that, in reality, the 

 hairs arise from within the rim of the theca, in a 

 single row (fig. 5.). These hairs are named in Bo- 

 tany, the TEETH of the fringe, or peristome ; the lat- 

 ter term desifrnatinff the rino^ of hairs. The nature of 

 the fringe varies in different genera ; sometimes it 

 consists of two rows of teeth, differing from each 



