XXIV] COMPARISON 217 



indicate G.pectinata and linearis?.^ holding an intermediate position between 

 the Gleicheniaceae and certain Ferns ranked with the Cyatheaceae. 



In respect of the gametophyte the intermediate features are no less 

 significant. Its general form in the Gleicheniaceae is reminiscent of that of 

 the Osmundaceae, a point supported by the long straight neck of the 

 archegonia. But it is from the antheridia that the clearest indications are 

 derived: for they are larger, and the spermatocytes are more numerous in 

 such a type as G. laevigata than has been observed in any of the Lepto- 

 sporangiate Ferns. But the numbers are variable within the species, and 

 even in the individual: in certain species which may be regarded as 

 specialised members of the Family the number of spermatocytes appears 

 to fall to a figure approaching that usual in Leptosporangiate Ferns. 



From these comparisons in respect of the several criteria mentioned it 

 appears that the Gleicheniaceae hold a singularly interesting intermediate 

 position between the Eusporangiate and the Leptosporangiate Ferns. This 

 conclusion is in full accord with their palaeontological history. There are 

 indications of the existence of similar Ferns in the Palaeozoic Period. But 

 the existence of true Gleicheniaceae from early Mesozoic times onwards is 

 fully made out, with a climax in the Chalk Period. Such a history might in 

 itself suggest that intermediate position which is so amply proved by detailed 

 comparison of the living representatives. Thus the two lines of evidence 

 mutually support one another. There are probably no other genera of hving 

 Ferns that serve so effectively as Gleichenia and Osnmnda to bridge the gap 

 between the Eusporangiate and the Leptosporangiate Ferns. The early 

 existence of the Gleicheniaceae, the Osmundaceae and the Schizaeaceae 

 shows that in early geological time intermediate forms existed between these 

 two branches of the Class. Their survivors of the present day serve to 

 demonstrate the essential unity of the Class of the Filicales, and to mark 

 some at least of those lines of modification which have been involved in the 

 evolution of the more recent Leptosporangiate t}'pes. 



Phyletic Grouping of the Family 

 The facts upon which a phyletic grouping 'of the Family may be based 

 are embodied in the preceding pages. Little alteration is required from the 

 systematic sub-division of the Gleicheniaceae now generally accepted. 

 Stromatopteris (Mettenius, 1861) is upheld as a substantive genus. The 

 further knowledge of the anatomy, heterophyll}-, and apparent heterospory 

 of Platyzoma (Smith, 1793) justify its reinstatement as another substantive 

 genus. The comprehensive genus Gleichenia (Smith, 1793) should on the 

 ground of the new facts relating to its anatomy, its sorus, sexual organs, 

 and dermal appendages be divided into three Sub-genera: viz. (i) Dicran- 

 opteris (Bernh.), a name already adopted in place of Willdenow's name 



