MOSSES AND LIVERWORTS 105 



In the Archegoniates the structure arising from the 

 fertilized egg is much more complicated than in any of 

 the algae. Here, also, the egg after fertilization secretes 

 a cell-wall about itself, but instead of remaining at rest 

 for a long time, growth begins almost at once. The 

 plant thus formed is . entirely different from the one 

 which produces the sexual organs, and the reproductive 

 cells to which it gives rise differ entirely from those of 

 the sexual plant. These cells are purely non-sexual in 

 character and capable of germinating at once. They 

 are spores which differ from the corresponding ones of 

 the green algae in being destitute of cilia and provided 

 with a very firm membrane which enables them to resist 

 extremes of temperature and dryness. 



The spores in all the Archegoniates are formed in 

 groups of four from the division of a common mother- 

 cell. The tissue from which the sporogenous cells arise 

 is termed the " archesporium." These spores on germi- 

 nation give rise, not to another spore-bearing plant, 

 but to the sexual one. This alternation of sexual and 

 non-sexual individuals is a constant characteristic of the 

 Archegoniates, and the two phases are known respec- 

 tively as the gametophyte (sexual) and sporophyte 

 (non-sexual), convenient terms which will be adopted 

 in the future discussion of the group. 



Among the lower Archegoniates, as in the algae, it 

 is the gametophyte which is predominant and the spo- 

 rophyte is small and inconspicuous, looking like a mere 

 appendage of the gametophyte ; but as we ascend, we 

 shall see how the gametophyte becomes more and more 

 subordinated to the sporophyte, which finally becomes 

 an independent long-lived plant, while the gametophyte 



