VII 



THE BRYINEAL 



203 



place in the ordinary way. Later the walls of the epidermal 

 cells become very thick and show a distinct striation (Fig. 

 1 01). By the formation of the stomata the green assimi- 

 lating tissue of the apophysis and central part of the 

 capsule are put into direct communication with the external 

 atmosphere. 



The lower part of the seta grows downward and penetrates 

 the top of the stem of the gametophyte, from which, of course, 

 it derives a portion of its sustenance. The centre of the seta 

 is traversed by a well-marked central cylinder, whose inner 

 cells are small and thin-walled, and are mainly concerned in 

 conducting water ; immediately outside of this is a circle of 



Fig. 100. — Longitudinal section of a fully-developed sporogonium oi Funaria hygrometrica, x about 

 40 ; s, seta ; a, apophysis ; sp, spores ; col, columella ; r, annulus ; o, operculum. 



thick-walled brown cells (Leptome of Haberlandt), and the 

 rest of the seta is made up of nearly similar thick-walled cells 

 which grow smaller towards the periphery. 



At maturity, as the supply of water is cut off from below, 

 the capsule dries up, and all the delicate parenchyma com- 

 posing the columella and inner part of the operculum, as well 

 as that between the spore-sac and the epidermis of the theca, 

 completely collapses, leaving little except the spores themselves, 

 and the firm cell walls of the peristome, and the cells connecting 

 the latter with the wall of the capsule. By the breaking down 

 of the unthickened lateral and transverse walls of the peristomial 

 cells, the outer and inner thickened walls are separated and 



