CHAPTEE XXIV 



THE BRYOPHYTES AND THE ESTABLISHMENT OF ALTER- 

 NATION OF GENERATIONS 



282. The bryophytes.* The division Bryophyta (meaning 

 moss plants) is the next great group of plants above the division 

 Thallophyta (Chapter xix), and includes two classes: (1) the 

 liverworts, or Hepaticce, and (2) the mosses, 

 or Musci. It is not best to define these 

 classes until the structure and life histories 

 of types from each group have been studied. 

 Furthermore, it is impossible fully to under- 

 stand the characters of the bryophytes and 

 thallophytes except when compared with 

 one another. Accordingly these matters 

 have been reserved for the final section of 

 this chapter under the heading Summary 

 of the Bryophytes and Thallophytes (Sees. F IG . 243. The anther- 

 300, 301). idium of a liverwort 



However, the bryophytes differ from the ( M cha *ia) 



thallophytes in two very important respects Antheridium in section, 



* L showing the outer cap- 



which may be briefly stated at once, for suie and the mass of 



they must be thoroughly comprehended in ^ cells within, in 



which are developed 

 order to understand the life histories of the 



liverworts and mosses. They can only be 

 made clear when illustrated through labora- 

 tory studies. These two differences are (1) in the sexual organs, 

 which are many-celled, and (2) in the appearance of a new stage 

 in the life cycle called the sporophyte. 



* To THE INSTRUCTOR : The introduction to this chapter assumes that the 

 life history of a liverwort or moss has been studied in the laboratory. 



276 



the minute two-ciliate 

 sperms shown at the 

 left. After Sachs 



