UEPATICM 



349 



here surrounded by a periantli, a loose bag-like slieath, which 

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

 length completely enclosing it ( F//. and F///.,I'ig. 2^b,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 Marcliantia 

 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 



Pig. 237. 



Fig. 238. 



Fig. 237.— Futile receptacle of Marchantia polyrrwrpha, seen from below. $t, its 

 atalk, curiously grooved ; er, one of the rays or the star-shaped receptacle ; /, one of 

 the sporogonia ; pc, pe^ perichtetia, which surround .''everal sporogonia. X 6.— After 

 Sachs. 



Fig. 238. — Plant of Plagiockila asplenioides. with the bilateral leafy axis below, p, 

 the perianth through whose top the sporogonium or cap--»ule has pushed ; o, an un- 

 lape sporogonium ; 6, 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 



