IIEPATIGJS. 



349 



here surrounded by a perianth, a loose bag-like sheath, which 

 grows up from below the base of the young sporogonium, at 

 length comijletely enclosing it ( F//. and F///.,Fig. 235, pp). 

 455. — The archegonia of the Liyerworts occur singly, as 

 in Riccia, Anthooeros, etc., or grouped together, as in Mar- 

 cliantia, Jungermannia, and their allies. In MarcTiantia 

 they grow in several clusters of four to six upon the under 

 surface of the spreading top (the fertile receptacle) of a 

 special branch of the thallus (Fig. 337). In many cases the 



Fig. 237. 



Fia. 238. 



Fig. 237.— Fertile receptacle of Mardiantia polymarpha, seen from below, st, its 

 stalk, curiously grooved ; sr, one of the rays of the star-shaped receptacle ; ./", one of 

 the sporogonia ; pc, pa, perichsetia, which surround several sporogonia. X 6.— After 

 43achs. 



Fig. 338.— Plant of Plagioehila asplenioides. with the bilateral leafy axis below, p, 

 the perianth through whose top the sporogonium or capsule has pushed ; a, an un- 

 xipe sporogonium ; &, a ripe sporogonium split open to permit the escape of the spores. 

 — After Prantl. 



sporogonium is, even when fully mature, sessile, or nearly so, 

 there being but a very short stalk developed; but in the 

 Jimgermanniacem, when the sporogonium is ripening, the 

 tissue at its base increases rapidly, and gives rise to a long 

 slender stalk, which pushes the spore-case through the dried- 

 up wall of the old archegonium, and raises it to the height 

 often of several centimetres (Fig- 338). 



456. — There are various ways in which the spores are set 

 free from the ripe sporogonium or capsule. In Riccia it 



