40 



BEITISH MOSSES. 



peristomes, (1) the division of the teeth at their free 

 ends, and (2) the presence of transverse markings, 

 generally of a darker colour than the intervening spaces. 

 A tooth thus marked is said to be trabeculated, i.e., 

 marked by trabeculae, or little beams. 



In one considerable family of Mosses, some of 

 which are very common on the tops of our walls, the teeth 

 are hair-like in length and delicacy, and are twisted into a 

 curious scroll like a lambent flame of fire. Fig. 24 

 represents one of these twisted peristomes, from which 

 the genus especially characterized by it has received from 

 some botanists the name of Tortula. 



Again, in another form, which exists in Polytrichum, 

 the teeth assume a very different appearance and connec- 

 tion. To make this intelligible I must refer to a portion 

 of the structure of the capsule to which I have not hitherto 

 referred, the columella, or little column, a central stem 

 which occupies the very axis of the 

 capsule ; this, in Polytrichum, 

 emerges from the mouth and ex- 

 pands into a tympanum or drum- 

 head, and the teeth arising from the 

 lip of the mouth join and support 

 this drumhead, leaving interspaces 

 between them something like long 

 narrow windows under the flat roof 

 of a circular tower, through which 

 the spores escape. Fig. 25 is a re- 

 presentation of this singular struc- 

 ture, in which p. marks the place of the peristome or girdle 



Fia. 25. Capsule and 

 peristome of Poly- 

 trichum. p. peris- 

 tome, t, tympanum, 

 after nature. A.F. 



