GROUP II. BRYOPHYTA : HEPATIC^. 



335 



cerotacese, the whole or part of the endothecium constitutes a 

 columella, a feature in which the Anthocerotacese resemble the 

 Musci. 



In the Riccieae (except Oxymitra) the whole archesporium is 

 sporogenous, whereas in all other forms some of the archesporial 

 cells are sterile, and in many they are developed into elaters, elon- 

 gated cells with spirally thickened walls, generally becoming free 

 from each other. 



FIG. 239. Comparative morphology of the sporogonium in the Hepaticas : diagrammatic 

 longitudinal sections. A Riccia ; B Marchantia; C Anthoceros ; D Radula. I-I basal 

 wall; /foot; st seta; am amphithecium ; end endothecium; or archesporium (shaded); 

 col columella. (After Goebel.J 



The sporogonium remains enclosed in the calyptra until the 

 spores are mature when, if a seta be present, it suddenly elongates 

 and ruptures the calyptra, which persists as a vaginula at its base. 

 The capsule opens either by the decay of its wall, or more gener- 

 ally by the splitting of the wall from the apex downwards into 

 valves ; in some Marchantieae a lid, the operculum, is formed and 

 the capsule is opened by the throwing off of the lid. 



