284 SPOROGONIUM OF MOSSES 



In a few Liverworts belonging to the genus Riccia, the 

 sporogonium, which is here embedded in the thallus, is of much 

 simpler construction, consisting merely of a spherical capsule 

 within whose one-layered wall only spores are produced. 



In Mosses the embryo elongates considerably at an early 

 stage, and soon acquires the shape of a rod tapering at either 

 end (Fig. 156, H and I). The lower extremity penetrates into 

 the tissue of the Moss-stem and forms the absorptive foot (/.), 

 which is, however, much less distinctly outlined than in Liver- 

 worts. Soon after, a swelling, the apophysis, appears on the 

 rod-shaped embryo, a little way above its middle, separating 

 the future seta and capsule. The apophysis, which plays a 

 part in the nutrition of the growing sporogonium, is a local 

 assimilatory region composed of cells rich in chloroplasts and 

 provided with abundant intercellular spaces (Fig. 156, A, ap.). 

 The epidermis here contains stomata (Fig. 156, F) like those of 

 higher plants, except that the septa between the guard-cells 

 break down at maturity, so that the latter form an oval canal 

 surrounding the pore (Fig. 156, G). 



The upper part of the embryo enlarges progressively, during 

 the subsequent development, to form the capsule, so that at 

 maturity the latter is usually far more prominent than the 

 apophysis, which, though it always remains recognisable, does 

 not grow much after its first formation (cf. Fig. 156, A). The 

 mature capsule is here also raised aloft by a considerable elonga- 

 tion of the slender stalk (Fig. 150), and again this causes rupture 

 of the calyptra. In Mosses, however, this takes place in such a 

 way that the upper part of the calyptra is carried up on the 

 capsule as a hood (Fig. 150, A, ca.). When this is removed, the 

 apex of the capsule is seen to be separated from the rest by a 

 slight constriction, and it is this part that becomes detached as 

 a lid to allow of dispersal of the spores. 



The internal structure is best studied in a longitudinal section 

 of a nearly ripe capsule (Fig. 156, A). Here the axis is occupied 

 by a rather broad column of thin-walled parenchyma (the 

 columella, Co.) passing below into the tissue of the apophysis (ap.) 

 and above into that of the lid (/.). Surrounding the columella 

 are two concentric cylinders of cells, separated by the granular 

 archesporium (a.), each mother-cell of which, as in Liverworts, 



