342 STUDIES IN FOSSIL BOTANY 



and probably Diplolabis, is of importance as evidence 

 against any direct connection between these genera 

 and the Ferns of later periods. Among the latter 

 dimorphism has appeared in most of the families, 

 but, except in the Ophioglossaceae, it is never a 

 family character. There is a strong presumption that 

 in Hymenophyllaceae, Schizaeaceae, Osmundaceae, 

 Cyatheaceae, and Polypodiaceae uniformity of foliage 

 is a more primitive condition than specialisation of 

 sporophylls, and that each of these families, as well 

 as the Gleicheniaceae and Marattiaceae, started with 

 sporangia borne on the ordinary frond. If this be so, 

 it implies that the typical Botryopterideae cannot have 

 been on the direct line of descent of the Lepto- 

 sporangiate Ferns. 



Vegetative, and especially anatomical characters, 

 must also carry considerable weight. The monostelic 

 structure, and the single petiolar bundle, suggest a 

 comparison with one of the four families, Osmundaceae, 

 Schizaeaceae, Gleicheniaceae, and Hymenophyllaceae. 

 The axillary shoots of Zygopteris indicate the last-named 

 group as that with which the analogy is most evident, 

 and other anatomical features confirm this indication. 

 The resemblance between the anatomy of one of the 

 larger species of Trichomanes and that of Zygopteris is 

 in fact very striking. 1 The stele of Trichomanes 

 reniforme, for example, has a simpler form than that of 

 the main stem in Z. Grayi, but the arrangement of 

 its elements is much like that in the fossil plant, 



1 See L. A. Boodle, " Comparative Anatomy of the Hymenophyllaceae, 

 Schizaeaceae, and Gleicheniaceae. I. Hymenophyllaceae," Ann. of Bot. 

 vol- xiv. 1900. 



