CHAPTER XXIV 



THE BRYOPHYTES AND THE ESTABLISHMENT OF ALTER- 

 NATION OF GENERATIONS 



282. The bryophytes.* The division Bryopliyta (meaning 

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

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

 liverworts, or ffepaticce, 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. p IG 243. The anther- 

 300, 301). iilimn of a liverwort 



However, the- bryophytes differ from the (^rchantia) 

 thallophytes in two very important respects Antheridium in section, 



showing the outer cap- 



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

 they must be thoroughly comprehended in sma11 cells Wlthm ' m 



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. 



275 



the minute two-ciliate 

 sperms shown at the 

 left. After Sachs 



