EOCENE FERNS. 



59 



The preceding table^ is full of suggestive interest and contains new evidence bearing 

 upon questions of the highest physical importance. 



In conclusion the principal types are recapitulated, in order to include details of 

 distribution and relationship to other recent and fossil Eerns omitted in the specific 

 descriptions. 



1. Gleichenia Hantgnensis, Wanklyn. (Page 43.) 



The only Gleichenia yet met with in the Eocene closely resembles G. dichotoma, the 

 sole existing representative of a well-defined subsection of the genus. The agreement 

 between them is striking, and extends to some minute details ; thus, the primary veins 

 are grouped and divided identically, the sori are identical in form, and, like in G. dicho- 

 toma, although usually situated on the upper or left hand secondary vein only, some- 

 times occur on both the secondary veins. This duplication of the normal single sorus to 

 each primary vein characterises De Bey and Ettingshausen's genus Didi/mosonis, a 

 genus which can hardly now be sustained since G. dichotoma has sometimes more than one 

 sorus to each primary vein. From the very fragmentary condition of the few specimens 

 figured by De Bey and Ettingshausen, it cannot yet be said that the possession of two 

 sori to each primary vein is a constant character. But were the fixity of this character 

 apparent there might now be hesitation in attaching specific value to it. The stipes, 

 rachis, and even the leaves in vernation were glabrous. 



Specimens of Gleichenia dichototna from Sydney and East Australia appear less rigid 

 and more membranous in character than those from elsewhere, and the Eocene species 



^ We have but to consider the almost complete absence of any records of other herbaceous plants, the 

 difficulty with which mountain species, which form a large proportion of fern-floras, or species with such 

 habits as OpJiioglossum, Asplenium ruta-mnraria, A. Ceterach,Sic., could find their way into these deposits, 

 to realise that we are probably only acquainted with those ferns whose habits favoured their preservation. 



But as nearly the whole of them have been found at Bournemouth, almost on one spot, and as 

 repeated search has brought no new forms to light, there can be little doubt but that we possess a nearly 

 complete knowledge of the Eocene lowland forest fern-flora of at least this locality, and probably no existing 

 area would furnish a greater variety of types under similar conditions. Although, therefore, the nuniber is 

 small compared to other orders of plants, we cannot help believing the fern-flora to have been extremely 

 rich, considering, as we have said, the complete absence of genera even as cosmopolitan as Asplenium, whose 

 habits are less favorable to preservation. 



The British and foreign Ferns provisionally placed together in this table were united, in some cases, 

 from a comparison of illustrations and descriptions only, and the grouping is therefore to a certain extent 

 but an indication of useful work still to be carried out. 



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