Lll] FOSSIL GNETALES 471 



identification is correct — and though the evidence is hardly con- 

 clusive the resemblance between the fragment from Renver and 

 an inflorescence axis of Gnetum is undoubtedly striking — it points 

 to the occurrence in a Pliocene European flora of a genus that is 

 now mainly tropical and which had not so far been recognised with 

 any certainty in a fossil state. 



The striking resemblance of Gnetum leaves to those of some 

 Dicotyledons is an obvious difficulty in the way of the identification 

 of impressions. 



It is among the oldest examples of supposed Dicotyledons that 

 search should be made for possible representatives of the genus 

 Gnetum. Among the earliest records of Angiosperms are those 

 described by Fontaine^ from the Patiixent series of the Potomac 

 formation which rests on Palaeozoic crystalline rocks and contains 

 the remains of a flora that is clearly Jurassic or Wealden in its 

 general facies; but with Jurassic Gymnosperms and Ferns are 

 associated some Dicotyledon-like leaves of ovate and linear form 

 for some of which Fontaine instituted the genera Rogersia, Fico- 

 phyllum, Proteaephyllum and referred others to Ficus, Sapindopsis 

 etc. A revision of the Patuxent fossils by Berry^ has led to a 

 considerable simplification in nomenclature and to the conclusion 

 that some at least of these Lower Potomac leaves are Gnetalean. 

 A comparison of some of Fontaine's figures of Ficus virginiensis, 

 species of Ficophyllum, Proteaephyllum, and Rogersia with a leaf 

 of Gnetum Gnemon reveals a very close agreement, as regards form 

 and venation, consistent with Berry's suggestion. It is by no 

 means unlikely that these forerunners of the Dicotyledonous type 

 that occur as foreign elements in a typical Jurassic flora, without 

 an admixture of undoubted Angiosperms like those which occupy 

 an important position in the upper beds of the Potomac formation, 

 may belong to plants more closely allied to Gnetum than to any 

 Angiosperm. Attention is especially called to the following species 

 as revised by Berry and illustrated in Fontaine's monograph: 

 Ficophyllum oblongifolium (Font.), Rogersia longifolia Font., Pro- 

 teaephyllum ovatum Font. 3 It is possible that a careful study of 



1 Fontaine (89) B. pp. 281 et seq. See also Seward (14'). 



2 Berry (11) pp. 64, 148, 499, etc. 



3 Fontaine (89) B. Pis. 139, 141, 144, 145, etp. 



