VI. 



THE BRYALBS 



2og 



similar section is made tlirougli an older capsule (Fig. iio), 

 it is evident at once that the enlarg-ement takes place mainly 

 below the junction of the operculum, and there is also a similar 

 but less pronounced increase in diameter in the operculum itself; 

 but there is a narrow zone at the junction of the operculum and 

 capsule, where the epidermal cells increase but little in depth, 

 while those above this point become very much lari^er and pro- 

 ject beyond them. This narrow zone of cells marks the point 

 where when ripe the operculum becomes detached. The latter, 



Fig. iio. — Longitudinal section of an older capsule of F. hygrometrica ; i, intercellular 

 spaces; sp, archesporium; r, cells between operculum and theca, X525. 



Up to the time the sporogonium is ripe, is composed of a close 

 tissue without any intercellular spaces. The epidermal cells, 

 seen from the surface, are seen to be arranged in spiral rows 

 running from the base to the apex. Its central part is made up 

 of large thin-walled parenchyma, continuous with the tissue of 

 the columella. The archesporium, therefore, is not continuous 

 over the top of the columella, as in Sphagnum and Andrecca, 

 but is cylindrical. The archesporium forms simply a single 

 layer of small cells, and occupies a very small part of the sporo- 

 14 



