448 ANNUAL REPORT SMITHSONIAN INSTITUTION, 19 3 8 



scraps of information, and it is desirable that this lack of precision 

 and paucity of evidence should be implied by the terminology which 

 a paleobotanist employs. If he has sufficient evidence to justify him 

 in assigning fossil leaves to the genus which includes Ginkgo biloba, 

 well and good; if he has no such evidence, then he admits the lack 

 of certainty by adopting the name Ginkgoites. It is, however, im- 

 possible in some instances to make a satisfactory choice between the 

 alternative generic names. For present purposes it is not worth 

 while to discuss tiresome though unavoidable questions of nomen- 

 clature: for the sake of simplicity, rather than in accordance with 

 strictly scientific considerations, the generic designation Ginkgo is 

 adopted in the following account of fossil leaves believed to belong 

 to trees which, if now living, would either be referred to Ginkgo or to 

 a separate and very closely related genus of the same family. 



FOSSIL LEAVES 



The periods of geological history with which we are concerned are 

 arranged as follows: 



Recent. 



Quaternary. 



'Pliocene stage. 

 Miocene stage. 

 Oligocene stage. 

 ^Eocene stage. 



Cretaceous. 



Jurassic. 



Rhetic. 



Triassic. 



Permian. 



Carboniferous. 

 As already stated, it is not absolutely certain, though by no means 

 improbable, that the maidenhair tree still exists as a wild tree: there 

 can be no doubt of its natural occurrence in Far Eastern forests 

 within the limits of the Recent period. Passing to the Quaternary 

 period, to a time separated from the present by many thousand years, 

 there is a record of the discovery of Ginkgo leaves by the Russian 

 paleobotanist, Kryshtofovich, at a locality on the Bureya River in 

 northeastern Siberia (approximately 50° N. lat.): good photographs 

 of the fossils have not been seen. Descending the geological scale 

 the next records are from Pliocene plant beds in France and Germany. 

 Well-preserved leaves were found near Frankfort on the Main very 

 similar in form and venation to the leaves of Ginkgo biloba, agreeing 

 also in the structure of the epidermal layer, though not identical in 

 certain details. Other examples from the Pliocene stage have been 

 described from the Rhone Valley, where forests formerly fringed the 



Tertiary* 



