The Origin of Land Plants 99 



gonium, show some interesting resemblances in 

 structure to those of the lower ferns. The arche- 

 gonium and antheridium in all their essential fea- 

 tures are very similar to those in the liverworts and 

 mosses, and, as in those, water is essential both for 

 the opening of the ripe reproductive organs and for 

 the conveyance of the motile sperms. Its de- 

 pendence upon water and the presence of these mo- 

 tile sperms clearly indicate the aquatic origin of the 

 gametophyte. 



There is much difference among the different 

 groups of pteridophytes in the degree of the 

 development of the gametophyte and as might be 

 expected, those forms which for other reasons 

 may be assumed to be the oldest and most primi- 

 tive types, are those in which the gameto- 

 phyte is most important and most nearly resembles 

 that of the hypothetical liverwort-like progenitors. 

 In some of the more primitive ferns (Fig. n, A), 

 the gametophyte may reach an inch or so 

 in length and may live for several years, not 

 always dying after the sporophyte has become estab- 

 lished. In some of the more specialized ferns, on 

 the other hand, like the so-called water ferns, the 

 whole life of the gametophyte may extend over less 

 than twenty-four hours. 



In their fertilization and early development of 

 the embryo-sporophyte, the ferns closely resemble 

 the simpler liverworts, but sooner or later there 

 is evident the development of special organs, 



