CHAPTER XXXIX 



GYMNOGRAMMOID FERNS 



In the opening paragraphs of Chapter XXXVIII it was pointed out that 

 the "Ptericleae" of Diels (Engler and Prantl, I, 4, p. 254) comprise the bulk 

 of the Pterideae of Hooker, together with his Grammitideae. It was further 

 noted that this association is based upon a diagnosis that is comprehensive 

 rather than exact, and that it was appHed without reference to evolutionary 

 or ontogenetic origin. As a consequence it places together groups which may 

 have had a quite distinct evolutionary story: this is probably the fact on 

 the one hand for the Ferns styled by Diels the Pterideae-Pteridinae, which 

 have been dealt with under the name of the Pteroid Ferns in the preceding 

 chapter; and on the other those which he designates the Pterideae-Gymno- 

 gramminae, -Cheilanthinae, and -Adiantinae, here to be styled the Gymno- 

 grammoid Ferns. On the ground of consecutive comparison of Ferns 

 clearly related to one another it has been shown in Chapter XXXVlll with 

 high probability that the former sprang from a bi-indusiate source, such as 

 is seen in the Dicksonioid-Dennstaedtioid series. A leading feature in the 

 argument has been the gradual disappearance of the lower indusium; for 

 this a high degree of physiological probability rests on the fact that, as the 

 sorus shifts from the marginal to a superficial position and the upper indu- 

 sium curls over, the lower indusium is no longer essential for protection, 

 which was its original function. In taking up the treatment of the Gymno- 

 grammoid Ferns, the first question that will arise will therefore be whether 

 any such argument will apply for them. Are any vestiges of the lower 

 indusium to be found? If not, there would appear to be no justification 

 drawn from the soral characters themselves for attributing to these Ferns a 

 common origin with the Pteroids, which had a bi-indusiate ancestry. It may 

 be stated at once that no such evidence is forthcoming for the Ferns ranked 

 as Gymnogrammoid. It will therefore be necessary to consider whether any 

 other types of non-indusiate Ferns of primitive type exist, in relation to 

 which the origin of a Gj^mnogrammoid state may be traced. Such primitive 

 types without any specialised indusium, and with sori already superficial, 

 and more or less extended along the veins, are to be found in the surviving 

 genera Todea and Plagiogyria, while the Schizaeaceae should also be borne 

 in mind, and particularly Mohria and Anemia. With these considerations 

 before us we may enter upon the study of the Gymnogrammoid Ferns. 



For purposes of convenient description here the Gymnogrammoid Ferns 

 may be grouped into four sections : 



I. Those which show a relatively primitive condition, as seen especially in 



