70 



STRUCTURAL AND PHYSIOLOGICAL BOTANY. 



596. These thecse may be considered minute leaves, having 

 the same gyrate mode of developement as the ordinary leaves 

 of the tribe ; their stalk the petiole, the annulus the midrib, 

 and the theca; itself the lamina, the edges of which are united. 



597. They would, therefore, be analogous to carpels, if it 

 appeared that they were influenced by the action of any vivi- 

 fying matter. 



598. MOSSES are increased by spores (590), contained 

 within an urn, or theca, or sporangium 31 * 316 , placed at the 

 apex of a stalk or seta, bearing on its summit a kind of loose 

 hood, called a calyptra 31 *, and closed by a lid or operculum. 



599. The inside of the theca has a central axis or columella, 

 and the orifice beneath the operculum is closed by teeth- like 

 processes, or a membrane called the peristome 313 318 . 



600. At the base of the theca is sometimes found a tumour 

 or struma 31 *, or an equal expansion named apophysis 319 . 



601. The number of the teeth of the peristome is always 

 some multiple of four. 



602. The calyptra originally grew from the base of the 

 stalk; but when the stalk lengthened, the calyptra was torn 

 away from its base and carried up, surrounding the theca. 



603. The calyptra may be understood to be a convolute 

 at; the operculum, another; the peristome, one or more 



