THE BRYOPHYTA: HEPATICAE, THE LIVERWORTS 413 



four, which become the columella. They represent the endothecium of 

 the Moss capsule, but in this case, though not in the Mosses, the spore layer 

 is formed from the outer zone of cells, the amphithecium . When fully 

 developed the sporogonium consists of a slender cylindrical upgrowth, very 

 like the cotyledon of an onion seedling. The sporogonium shows, in transverse 

 section (Fig. 396), an epidermis with well-developed cuticle and stomata ; 



STOMA 



CAPSULE WALL 



SPORE TETRADS 



COLUMELLA 



Fig. 396. — Anthoceros loevis. Transverse section through middle part 

 of sporogonium. {After Goehel.) 



three to four layers of amphithecial cells and then a layer of spores grouped 

 in tetrads round the central columella, which is usually shrunken to small 

 dimensions. Owing to their close grouping in tetrads each spore is pyramidal 

 in shape and has a yellowish, warted wall. Among the spores are short 

 chains of one to four small cells of irregular shape which are called pseudo- 

 elaters and probably have a similar function to true elaters. 



In longitudinal section (Fig. 397) the spore layer is seen to extend over 

 the top of the columella like a saddle, a feature shared only with Sphagnum. 

 At the base of the sporogonium the lowest portion of the columella and its 

 surrounding cells remain meristematic, and by intercalary growth in this 

 region the sporogonium gradually elongates to a length of 2 or 3 cm. In 

 any one sporogonium, therefore, all stages of development may be seen. 



