CHAP. IV.] MUSCI. 467 



in time rises on a stalk of its own, carrying 

 away one of the leaves with it on its head. 

 This is the theca, and the leaf it carried away, 

 and which resembles an extinguisher, is called 

 the calyptra, and it remains on till the sporules 

 are nearly ripe. When the calyptra falls, the 

 theca is found to be covered with a little lid 

 called the operculum ; which also falls off in 

 time, and shows the mouth or stoma of the 

 theca. This mouth is sometimes naked, and 

 sometimes covered with a kind of film ; but 

 generally it is surrounded by a row of long, 

 slender, hair-like teeth called the peristome or 

 fringe. When there are two rows of these hair- 

 like teeth, the inner ones, which are finer than 

 the others, are called the cilia ; and the number 

 of both the cilia and the teeth is always some 

 number that can be divided by four. In the 

 cavity of the theca is a central axis called the 

 columella, and around that are found the spo- 

 rules, kept together by the lining of the theca, 

 which forms a kind of open bag. This is the 

 usual construction of all the numerous genera of 

 mosses ; but in some kinds, as for example in 

 the Hair-moss (Poli/trichium), in addition to 

 the theca, a number of granules are found 

 among the leaves, which are said to be capable 

 of producing young plants. 



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