IX MARATTIACE^—ISOETACE.^E 297 



of all living Ptcridophytcs, seemed to be the nearest to the 

 Bryophytes. Subsequent study of the eusporangiatc Ferns 

 has strengthened that belief, and from a comparison of these 

 with OpJiioglossuni on the one hand and the Anthoceroteae on 

 the other, it seems extremely likely that the latter represents 

 more nearly than any other group of living plants the form 

 from which the Pteridophytes have sprung, and that in the 

 series of the Filicineae at any rate, Ophioglossum comes nearest 

 to the ancestral form. Of course the possibility of OpJiioglossum 

 being a reduced form must be borne in mind, and the sapro- 

 phytic habit of the prothallium may perhaps point to this ; still, 

 whatever may be its real character, there is little doubt that it 

 is the simplest of the Filicineae. 



The resemblances between OpJiioglossum and the Anthocero- 

 teae are not confined to the sporophyte. The sexual organs — 

 and this is true of all the eusporangiate Pteridophytes — show 

 some most striking similarities that are very significant. It 

 will be remembered that in the Anthoceroteae alone among the 

 Bryophytes the sexual organs are completely submerged in the 

 thallus — the antheridia being actually endogenous. It will be 

 further remembered that in the eusporangiate Filicineae a similar 

 condition of things exists. 



In all the Hepaticae the axial row of cells in the archegonium 

 terminates in the cover cell, which by cross-divisions forms 

 the group of stigmatic cells of the neck. In the Anthoceroteae 

 this terminal group of cells is the only part of the archegonium 

 neck that is free, the lateral neck cells being completely fused 

 with the surrounding tissue. This arises from the archegonium 

 mother cell not projecting at all, but we have seen that in 

 cross-section a similar arrangement of the cells is presented to 

 that found in the young archegonium of other Hepaticae. In 

 the Filicineae a similar state of affairs exists, but the divisions 

 in the mother cell are, as a rule, not so regular. Still, eg. 

 Isoetes, it is sometimes easy to see that the mother cell (so-called) 

 of the archegonium is triangular when seen in cross-section, and 

 cut out by intersecting walls in exactly the same way as the 

 axial cell in the Bryophyte archegonium. In short, what is 

 ordinarily called the mother cell of the archegonium in the 

 Ferns is really homologous with the axial cell only of the young 

 archegonium of a Liverwort. A comparison of longitudinal 

 sections of the young archegonium of Marattia, for instance, 



