54 



eventually it ruptures near its base. The upper 

 portion is carried up on top of the Sporogonium and 

 forms the so-called Calyptra or cap. The lower 

 portion forms a sort of a saucer-like sheath at the 

 base of the seta and is called the Vaginula. 



The Theca (or Spore Capsule) is fusiform in shape 

 and consists at first of a mass of undifferentiated 

 tissue, the central portion of which persists and forms 

 the columella. Surrounding the columella is the 

 spore sac, and next to this a large air cavity traversed 

 by cellular 61aments of cells. The extreme outside 

 consists of a wall a few cells in thickness, the external 

 layer is considerably thickened. 



(a) Formation of spores. Each spore mother cell 

 gives birth to fourspoies formed tetrahedrally. 



(b) Dehiscence. The Theca dehisces hj detaching 

 its upper portion in the form of a lid called the 

 Operculum. Certain cells above the level of the 

 columella become fibrously thickened, and form a 

 complete ring. This is called the Amiulus, and it is 

 the annulus which contracts and casts oflt the 

 operculum. 



(c) The Peristome. Before the operculum is cast 

 off — the peristome — a special arrangement to facili- 

 tate the dispersion of the spores is elaborated. 



Directly above the air cavity and immediately 

 within the epidermis a single continuous lajer of 

 cells becomes thickened. This layer extends aJl 

 round the theca and reaches from the annulus to the 



