XV SUMMARY AND CONCLUSIONS 511 



plants. Indeed the sporogonium of AntJioceros is much more 

 like a small Ophioglossmn, for example, than it is like the 

 sporogonium of Riccia. 



The Mosses, like the foHose Liverworts, seem to represent 

 a modern, extremely specialised type, with no direct connection 

 with higher forms. Undoubtedly related to the Anthoceroteae 

 through SphagjiHin, their further development has diverged 

 farther and farther away from the other Archegoniatae, until in 

 the Bryineae both gametophyte and sporophyte have little in 

 common with them. 



The three classes of the Pteridophytes, while they differ 

 strongly in the form of the sporophyte, are yet so much alike 

 in the essential characters of the sexual generation, as to make 

 it inconceivable that they can have originated from very widely 

 separated ancestors. The more closely the gametophyte is 

 studied in all of them, the more evident becomes the strong 

 resemblance to the Anthoceroteae, w^hose sporogonium has 

 always been recognised as the nearest approach to the 

 sporophyte of the vascular Archegoniates. This is notably 

 the case when we consider the structure and development of 

 the sexual organs, which in the Anthoceroteae differ so re- 

 markably from those of the other Muscineae. Whether the 

 submersion of the archegonia and antheridia in the thallus is 

 the result of the cohesion of an envelope, such as is formed 

 about these in SpJicerocarpus or Riccia, it is impossible to 

 say, as there is no trace of any such process in the develop- 

 ment of the sexual organs in any of the investigated 

 species. 



The probable homology of the four -rowed neck of the 

 archegonium of the Pteridophytes with the cover cells only of 

 the Liverwort archegonium, has already been discussed at length 

 in a preceding chapter. It is quite possible that a similar 

 correspondence may exist between the antheridium in the 

 lower Pteridophytes and the Anthoceroteae. It will be re- 

 membered that in the latter the single antheridium, or group 

 of antheridia, arises from the inner of two cells formed from 

 the division of a superficial cell of the thallus, and that the 

 inner cell may either give rise to a single antheridium, or more 

 commonly, by repeated longitudinal divisions, a group of 

 antheridial mother cells is formed. The whole process is 

 strikingly different from the development of the superficial 



