298 MOSSES AND FERNS chap. 



with that of Notothylas, will show this clearly. From this it 

 follows that the four-rowed neck of the Pteridophyte archegonium 

 does not correspond to the six-rowed neck of the Bryophyte 

 archegonium, but only to the group of cells formed from the 

 primary cover cell, and is a further development of this. The 

 relatively long neck of the archegonium in the more specialised 

 forms, e.g. Botrychium Virginianum, and especially the lepto- 

 sporangiate Ferns, must be regarded as a secondary develop- 

 ment connected probably with fertilisation. The shifting of 

 the archegonium to the lower surface of the gametophyte has 

 probably a similar significance. \x\ B. Virginianum, however, 

 the archegonia are borne normally upon the upper side of the 

 thallus, as in the thallose Liverworts. 



It is possible that a similar relation exists between the 

 antheridia of the eusporangiate Ferns and that of the Antho- 

 cerotea^. In both cases the formation of the antheridium 

 begins by the division of a superficial cell into a cover cell and 

 a central one. The former divides only by vertical walls in the 

 Marattiacece, but in Ophioglossmn and the Anthoceroteae it 

 becomes two-layered. In the latter the central cell may form 

 a single antheridium, or it may produce a group of antheridia, 

 but in the others it divides at once into a mass of sperm cells. 

 By the suppression of the wall in the antheridium of an 

 Anthoceros where only one antheridium is formed, there would 

 be produced at once an antheridium of the type found in 

 Ophioglossum, and by a further reduction of the division of the 

 cover cell, by which it remains but one cell thick, the type 

 found in Marattia would result. 



Such an origin of the antheridium of the Filicineae is, at 

 any rate, not inconceivable, while not so obvious perhaps as 

 the resemblances in the archegonium, and is simply suggested 

 as a possible solution of a very puzzling problem. 



The Marattiacese agree closely among themselves, and the 

 structure of the gametophyte is like that of the Ophioglossaceae, 

 so far as the latter is known, and also offers most striking 

 resemblances to the Hepaticae. The long duration of the 

 prothallium here, and its persistence after the sporophyte 

 is independent, as well as the long dependence of the latter 

 upon the gametophyte, are all indications of the low rank of 

 this order. The sporophyte, v\'hile showing many points of 

 resemblance to the Ophioglossaceae, still differs very much 



