VI. 



THE DRV ALES 



Stcgocarpcc 



217 



Very much the larger numljer of Mosses belong to this 

 group, which is primarily distinguished from the foregoing by 

 the presence of an operculum. Of course among the 7000 or 

 more species belonging here there are many differences in struc- 

 ture ; but these are mainly of minor importance morphologically, 

 and only the more important differences can be considered here. 



As we have already seen, there is great uniformity in the 

 growth of the stem, which, with the single exception of Fis- 

 sideiis, has always a three-sided pyramidal apical cell. In 

 Fissidcns this is replaced by a two-sided one, 1)ut even here it 

 has been found (Goebel (8), p. 371) that the underground 



Fig. 117. — Cyathophornm pennatum, showing three rows of leaves; sp, sporophytes, 



stems have a three-sided initial cell, which is gradually replaced 

 by the two-sided one after the apex of the shoot appears above 

 ground. In Fissidcns the leaves are arranged in two rows cor- 

 responding to the two sets of segments, and are sharply folded, 

 so that the margins of the leaf are covered over by those of the 

 next older ones, leaving only the apex free. A similar arrange- 

 ment is found in the genus Bryoziphion (Eustickia), but here 

 there is a three-sided apical cell, and the two-ranked arrange- 

 ment of the leaves is secondary. In CyathopJwritm (Fig. 117), 

 there are two rows of large dorsal leaves and a row of much 



