550 FILICALES 



ancestor. If the attempt be made to .sketch the characters of that ancestry 

 they would be as follows : Probably like other primitive Ferns the early 

 Schizaeaceae had an upright, dichotomously branching stock (retained until 

 after the leading soral characters were established), with radially disposed 

 leaves, which also branched dichotomously : a protostelic structure (retained 

 till after Lygodium had assumed its creeping habit), and a relatively simple 

 leaf, as indicated by the single strand of the leaf-trace. On the surfaces were 

 simple filamentous hairs. The monangial sori were probably superficial, as 

 indicated by Senftcnbtrgia and Klukia, with a tendency towards the margin 

 realised in the more modern forms. The sporangia were relatively large, 

 with the annulus consisting of more than a single series of cells. 



Of the living forms Lygodium represents structurally the most primitive 

 type, being protostelic. Subsequently the stele dilated, perhaps to accommo- 

 date the enlarging leaf-traces, 1 as seen in the genus Schimea ; and became 

 even dialystelic, as in Aneimia and Mohria ; but the section Aneimiorrhiza 

 probably assumed its prone habit before the solenostele became dialystelic. 

 On this view Aneimia and Mohria would be anatomically the most advanced 

 types. This harmonises with the facts relating to spore-output : for on this 

 ground also Lygodium would be the most primitive, and the other genera 

 would have proceeded further towards reduction in number of the sporo- 

 genous cells. It is in Lygodium also that Zeiller recognised that more 

 complex structure of the annulus which corresponds to that of the earlier 

 fossils. 



There is, however, another, and from its entire independence of the 

 characters compared above, a most important feature, which marks off 

 Aneimia and Mohria as advanced genera in the family. Heim, 2 in 

 selecting organs which are typical for the divisions of the Ferns and 

 recur under altered cultural conditions, lays great stress upon the structure 

 and mode of dehiscence of the antheridium, of which he recognises two 

 types : Type A, in which at maturity the cap-cell breaks away ; this includes 

 the Osmundaceae, Gleicheniaceae, Hymenophyllaceae, Cyatheaceae, Dick- 

 sonieae, and Lygodium ; it is, in fact, characteristic of those Ferns which are 

 usually held as primitive. Type B, in which the antheridium has a star-like 

 dehiscence, includes Aneimia a"hd Mohria, and the whole body of the Poly- 

 podiaceae : thus these genera share with the later and presumably derivative 

 Ferns 3 a character by which they differ from Lygodium. Accordingly, on 

 their anatomy, on their spore-output, and on the mode of dehiscence of the 

 antheridium Aneimia and Mohria appear relatively advanced, and Lygodium, 

 which itself goes back to the Cretaceous Period, is relatively primitive. 

 Any converse view will have to meet not only one, but all of these 

 lines of evidence. 



1 Boodle, Ann. of Bot., 1903, p. 530. -Flora, 1896, p. 329, etc. 



3 Heim notes also other characters of the gametophyte in which Aneimia and Mohria 

 differ from Lygodium : so that the distinction is not based merely on the antheridial 

 dehiscence, but is more general. 



