200 



MOSSES AND FERNS 



CHAP. 



succession is the same, except for the formation of the arche- 

 sporium. Almost as soon as the capsule is recognisable, the 

 first indication of the operculum or lid becomes evident. 

 About half-way between the extreme apex of the sporogonium 

 and the top of the apophysis, a shallow depression is noticed 

 extending completely round the capsule and separating the 

 sharply conical apex from the part below. An examination of 

 a longitudinal section at this point shows that at the point of 

 separation the epidermal cells of the opercular portion are 



Fig. 98. — Longitudinal section of an older capsule of F. hygroineti-ica ; /, intercellular spaces ; 

 5/, archesporlum ; r, cells between operculum and theca, X 525. 



much narrower than those immediately below. Examining 

 the tissues farther in, the archesporium is seen to extend only 

 to a point opposite the base of the operculum, and the same is 

 true of the row of large cells where the air-space is formed. 

 If a similar section is made through an older capsule (Fig. 98) 

 it is evident at once that the enlargement 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 oper- 

 culum and capsule, where the epidermal cells increase but 



