HEPATIC^!. 



349 



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

 grows up from below the base of the youn^ sporogonium, at 

 length completely enclosing it ( VII. and J 7 7//.,Fig. 235, pp). 

 455. The archegonia of the Liverworts occur singly, as 

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

 chantia, Jungermannia, and their allies. In MarcJiantia 

 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. 237). In many cases the 



FIG. 237. 



FIG. 238. 



stalk 



Fig. 237. Fertile receptacle of Marchantia polymorpha, seen from below, ft, its 

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

 the sporogonia ; pc, pc, perichaetia, which surround several sporogonia. x 6. After 

 Sachs. 



Fig. 238. Plant of Plagiochila aaplenioides. with the bilateral leafy axi below, p, 

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

 ripe sporogonium ; b, 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 

 Jungermanniacece, 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. 238). 



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

 free from the ripe sporogonium or capsule. In Riccia it 



