582 FILICALES 



Various fossil fructifications from early geological formations have been 

 referred to the Hymenophyllaceae with more or less reason. The Devonian 

 Palaeopteris hibernica may be put aside as insufficiently known, while it 

 shows no distinct evidence of Hymenophyllaceous affinity : moreover, the 

 presence of its stipules is against it. In Hymenophyllites Weissii, Sch., 

 figured by Schimper from the coal of Saarbrucken, the reference is chiefly 

 upon the sorus as a whole, while the sporangia themselves were not 

 distinguished, or described in detail. Perhaps the best authenticated case 

 is that of Hymenophyllites delicatulus ( = H. quadridactylites (Gutb. Zeiller), 

 described and figured by Zeiller. 1 Here the sori were borne on the distal 

 ends of the pinnules : he was also able to recognise and draw the sporangia, 

 with an oblique annulus, which corresponds very closely with that of a 

 modern Filmy Fern. The original specimens were examined by Solms- 

 Laubach, who concluded that the fact is correctly stated, and no other 

 interpretation of the figures is possible. 2 Scott, however, remarks 3 that 

 the evidence as to the position of the reproductive organs on the leaf is 

 not sufficient to place the affinities of these fossils beyond doubt. 



It must be admitted that the evidence of existence of Hymenophyllaceous 

 fructifications from the Primary rocks is insufficient. It does not, however, 

 appear essential to the position to be ascribed to the Hymenophyllaceae 

 below that their early existence should be established, though their occurrence 

 even in the primary rocks would readily accord with the view here enter- 

 tained of their origin from the protostelic Simplices. 



ANATOMY. 4 



The most obvious structural peculiarity of the Hymenophyllaceae is the 

 " filmy " texture of their leaves : the lateral wings throughout are pellucid 

 owing to the absence of intercellular spaces, while there are no stomata 

 upon them. Usually the flattened region consists of only a single layer of 

 cells, though in some cases, such as T. reniforme and H. dilatatum^ 

 there may be three or four layers, but still without intercellular spaces. 

 The question naturally arises whether this filmy character is primitive or 

 the result of special adaptation. In Prantl's view it was held to be primitive, 

 and indicated an affinity with the Mosses ; but there are many reasons 

 for rejecting this, and seeing in the simple structure a specialised and 

 reduced character. It is plainly suited to the moist habitats in which the 

 Hymenophyllaceae mostly live : while on the other hand quite a number 

 of Ferns living in moist surroundings, but of divers affinity, show the same 

 character in varying degree : it is seen in Danaea crispa, Endres, and in 

 D. trichomanoides. Spruce, MMS. ; but in these several layers of cells are 

 present, with intercellular spaces : it is seen in various degrees in the 

 Leptopteris section of Todea, and most clearly in T. superba : also in 



1 Ann. Sci. Nat., Ser. 6, vol. xvi. 2 Palaeophyfology, p. 157. s Studies, p. 264. 



4 See Boodle, Ann. of Bot., xiv., p. 455, where the literature is fully referred to. 



