EOCENE FERNS. 



61 



regretted that no collector should have secured specimens exhibiting its growth in a 

 more satisfactory manner. Remains of forked stems, 3 to 5 mm. in width, associated 

 with the pinnae, are doubtless the thicker parts of the rachis, and show that these and 

 the fronds were of large size. 



This description, although differing in some respects from the former one, is, I 

 believe, more correct, being based upon a larger number of fragments. 



G. dichotoma is almost universally distributed in Tropical and sub-Tropical regions, 

 but varies much in habit. The characters given above and the glabrous leaves in 

 vernation and the stipes bring the fossil more distinctly near to the Australian than to any 

 other of the representative types of the species. 



Although rare or absent in the Eocenes, Gleichenias are abundant in the supposed 

 Neocomian and Upper Cretaceous rocks of Greenland. Heer has separated the 

 fragments into sixteen species, although the greater part, when compared with G. glauca} 

 their nearest existing representative, seem to come well within the limits of variation of 

 that species at the present day, even if specimens from one locality only are examined. 

 The presence of the genus in these high latitudes is repeatedly alluded to by Heer as 

 indicating a former approach to a tropical climate in the Arctic regions. Yet Gleichenias 

 now flourish in the rigorous climates of the Magellan and Falkland Isles, S. lat. 53°, 

 which have an isotherm of 45°, and are also found on the mountains of Tasmania and on 

 the Andes at an altitude of 10,000 feet, which Humboldt places at the level of gentians 

 and near the limit of arborescent vegetation. It is instructive to notice that while the 

 fossil Gleichenia of the Eocene of our latitude has its nearest ally in the distinctly tropical 

 G. dichotoma, the living representative of all the Arctic forms should be the only one 

 still ranging into the northern temperate regions in China and Japan. 



2. Adianttjm apalophtllum, Saporta. (Page 42.) 



The British fossil examples are detached pinnas of small size, like those found at 

 Sezanne, but preserving in some instances the arrangement of the sori. They differ from 

 the existing European species in the linear instead of obversely reniform arrangement of 

 the sori, and in being dimidiate, yet no species bears a greater general resemblance to them 

 than A. Capillus- Veneris. A.formosum, from the Arctic Neocomian, supposed by Heer to 

 be an Adiantum with small simple reniform fronds, has the stem and appearance of one of 

 the Ginkgos, which are everywhere characteristic of the secondary rocks in those regions, 

 nor was anything advanced to support his view. No certain Adiantum is known from 

 the Polar Tertiary flora, and but mere indications of it from the Miocenes of Europe. The 

 Oligocene of Armissan has, however, yielded a portion of a frond with nearly fifty cuneate 



1 G. longissima, Hooker, ' Synop. Filicum.' 



