198 STUDIES IN CRYPTOGAMS 



increases in size to accommodate and protect the young growing cap- 

 sule. It is finally torn loose and carried up on the spore-case. The 

 mouth of the capsule is closed by a circular lid, the operculum, having 

 a conical projection at the center. The operculum soon drops, or it 

 may be removed, displaying a fringe of sixty-four teeth guarding the 

 mouth of the capsule. 



This ring of teeth is known as the peristome. In most mosses the 

 teeth exhibit peculiar hygroscopic movements, i.e., when moist they 

 bend outwards and upon drying curve in toward the mouth of the 

 capsule. This motion, it will be seen, serves to disperse the spores 

 gradually over a long period of time. 



Not the entire capsule is filled with spores. There are no elaters, 

 but the center of the capsule is occupied by a columnar strand of tis- 

 sue, the columella, which expands at the mouth into a 

 thin, membranous disk, closing the entire mouth of the 

 capsule except the narrow annular chink guarded by the 

 teeth. In this moss the points of the teeth are attached 

 to the margin of the membrane, allowing the spores to sift 

 out through the spaces between them. 



When the spores germinate, they form a green, 

 branched thread, the protonema. This gives rise directly 

 to moss plants, which appear as little buds on the thread. 

 When the moss plants have sent their little rhizoids into 

 the earth, the protonema dies, for it is no longer necessary 

 for the support of the little plants. 



FERNS 



The adder's tongue fern, Ophioglossum vulgatum, 

 shown in Fig. 368, is one of a peculiar type of ferns be- 

 longing to the family Ophioglossaceae. This plant has a 

 short, subterranean stem from which a single frond unfolds 

 each year. The roots arise near the bases of the leaves. 

 368. The leaves are curiously ' divided into a sterile and a 

 Ophioglossum fertile part, the latter being a sporophyll. The sterile part 

 has a tongue-shaped blade which is narrowed to a petiole. 

 The young leaves are inclosed by the sheathing base of the petiole. 

 The growth is very slow, so that it takes several years for each leaf to 

 develop before it is ready to unfold. During its development each leaf 

 is sheathed by the one preceding it. 



The sporophyll is elevated on a stalk arising near the base of the 

 sterile part of the frond. The upper part consists of a spike bearing 



