82 



A TEXT-BOOK OF BOTANY. 



producing a sporogonium consisting of a short stalk which is 

 embedded in the tissues of the gametophyte, and a capsule (spor- 

 angium). The latter at maturity dehisces or splits and sets free 

 the spores, which are assisted in their ejection by spirally banded 

 cells called " elaters " (Fig. 48, C-F). The spores on germination 

 give rise to a protonema which then develops a thallus bearing the 

 sexual organs. As in the mosses, the sporogonium represents the 

 asexual generation known as the sporophyte. 



Liverwort Groups. There are three important groups of 



chl 



FIG. 47. Transverse section through the thallus of Marchantia Polymorpha. A, 

 middle portion with scales (b) and rhizoids (h) on the under side; B, margin of the thallus 

 more highly magnified, showing colorless retieulately thickened parenchyma (p), epidermis 

 of the upper side (o), cells containing chlorophyll (chl), air pore (sp), lower epidermis (u). 

 After Goebel. 



Liverworts: (i) The MARCHANTIA Group (Fig. 46), in which 

 the thallus is differentiated into several layers and so somewhat 

 thickened. Another character is the diversity in form of the 

 sexual organs, which range from those which are quite simple to 

 those which are highly differentiated. In Riccia the sexual organs 

 are embedded on the dorsal (upper) side of the thallus, while in 

 Marchantia they are borne upon special shoots, one, which has a 

 disk at the apex that bears the antheridia, known as the antheridio- 

 phore, and another whose summit consists of a number of radiate 



