330 The Botanical Gazette. [December, 



seem to warrant the assumption that in the Polypodiaceae we 

 have to do with a group of comparatively modern forms that 

 have arisen from the more ancient Eusporangiatae through 

 the Osmundaceae, Gleicheniaceae and Cyatheaceae, which fami- 

 lies constitute a quite natural series. The two families, Hy- 

 menophyllaceae and Schizaeaceat\ while evidently connected 

 with the lower members of this series, seem to form two off- 

 shoots from the main line of ascent, and the former is prob- 

 ably a degenerate group whose peculiarities are largely due to 

 the effects of environment. The affinities of the Hymenophyl- 

 laceae seem to be with the Gleicheniaceae and Osmundaceae. 

 The form of the sporangium and spores, as well as the pro- 

 thallium and sexual organs, is of the type found in these 

 groups. The branching filamentous prothallium, upon the 

 importance of which too much stress has been laid, is by no 

 means rare in Osmund a Claytoniana under certain circum- 

 stances, and the form of the sexual organs is very similar. 



As to the sporophyte, the Ophioglosseae form a natural se- 

 ries with Opliioglossnm at the bottom, and such species of 

 Botrychium as R. Virgiuianum at the top, the latter connect- 

 ing the group with the Osmundaceae. 



The Marattiaceae, as might be expected of such ancient 

 forms, show affinities with both the Osmundaceae and Ophio- 

 losseae, and may perhaps be regarded as a branch of the 





original stock that, beginning very far down, reached its 

 maximum development in the Carboniferous era, and then 

 declined. Whether, as suggested by Bower, 1 the sperma- 

 phytes have arisen from the same stock, must at present re- 



main conjectural. 



The forms hitherto discussed are the so-called isosporous 

 forms. Among the existing pteridophytes, however, are four 

 very distinct groups in which spores of two kinds are found, 

 viz.: Selaginellere, Isoeteas, Marsiliaceae, and Salviniace*. 



The first of these is evid 



ypodi 



and the third to the Polypodiaceae; but the affinities of the 

 others are not so clear. The Salviniaceae while clearly 

 enough belonging to the Leptosporangiatas, and related to the 

 lower members of the series, still are so peculiar that it is not 

 easy to decide where they should be placed. Prantl - sug- 

 gests th e Hymenophyllaceae as their nearest allies, and prob- 



1 Annals of Botany, Vol. Ill p -,$7 

 8 The Schizaeaceae, p. 153. 



