596 MOSSES AND FERNS chap. 



or neutral generation, which claims oilr principal attention, 

 and not the much reduced gametophyte. 



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 

 divergent ancestors. The more closely the gametophyte is 

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

 resemblance to the Anthocerotes, whose sporogonium has 

 always been recognised as the nearest approach to the sporo- 

 phyte of the vascular Archegoniates. This is notably the case 

 when we consider the structure and development of the sexual 

 organs, which in the Anthocerotes differ so remarkably from 

 those of the other Muscinese. Whether the submersion of the 

 archegonia and antheridia in the thallus is the result of the cohe- 

 sion of an envelope, such as is formed about these in Sphcurocar- 

 pus or Riccia, it is impossible to say, but there is no trace of any 

 such process in the development of the sexual organs in any of 

 the investigated species. 



The probable homology of the four-rowed neck of the arche- 

 gonium 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 cor- 

 respondence may exist between the antheridium in the lower 

 Pteridophytes and the Anthocerotes. It will be remembered 

 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 antheridia in the other groups 

 of Liverworts. In all of the homosporous Pteridophytes except 

 the leptosporangiate Ferns, however, the first division in the 

 antheridial cell is exactly as in the Anthocerotes; but instead of 

 the inner cell developing into a distinct antheridium, the whole 

 of it is devoted to the formation of sperm cells. It seems not 

 improbable that this type of antherirlium may have been derived 

 from one like that of the Anthocerotes by the suppression of 

 the parietal cells of the antheridium. 



Aside from the forms without chlorophyll, which are prob- 



