DEVELOPMENT OF PLANTS 



293 



often enlarged and provided with air spaces and stomata, thus 

 constituting the chief photosynthetic apparatus of the sporophyte 

 (Fig. 210, 3^). The entire surface of the capsule is protected 

 by a well-developed epidermis but at the top a lid or operculum 

 is cut off by a ring of rather delicate mucilage-bearing cells, 

 the annulus, which swells at maturity and so assists in casting off 

 the operculum (Fig. 210, 3, r). Below the operculum a layer of 



Fig. 211. Structure of capsule of Fiinaria: 5, capsule with calyptra, 5^, 

 removed. 6, section of nearly mature capsule — sp, spore-forming cells sur- 

 rounded on outside b}' loosely arranged chlorophyll-bsaring cells; 0, oper- 

 culum; r, annulus; p, peristome; a, apophysis. 8, magnified view of a 

 portion of the capsule, showing the annulus, r, and the thick-walled cells 

 of the peristome, p, which are attached at their base to the epidermis by 

 a double row of cells; sp, spore-forming cells. 7, the cells shown in 8, p, 

 have split apart, thus forming the inner and outer teeth-like segments of 

 the peristome. — After Sachs. 



