CONIFERAE 609 



Cordaitean leaves to some points. He regards 

 Prepinus as a probable ancestor of the true Pines. 1 



. Fossils from beds of much greater age — the 

 Rhaetic, for example (Schizolepis) — have been referred 

 to Abietineae, but the evidence does not seem to be 

 decisive. 



Cupressineae have not been traced with certainty 

 very far back, though twigs and cones of Cupressineous 

 habit occur in the Jurassic. A fossil species of the 

 recent genus Callitris (Widdringtonid) has been 

 described from the Upper Cretaceous of Moravia, 

 and seems to be an extraordinarily clear specimen, 

 with characteristic cones of both sexes well preserved. 2 

 If a recent genus already existed, in a characteristic 

 form, in Cretaceous times, it is certain that the group 

 to which it belongs must have been of very considerable 

 antiquity, but we can only look to future discoveries 

 for further light on its history. 



The Taxaceae, as now limited (exclusive of Ginkgo), 

 have not been traced back with certainty to a lower 

 horizon than the Cretaceous, though branches with 

 leaves like those of the genera Cephalotaxus and 

 Podocarpus have been described from the Potomac 

 formation, probably of about Wealden age. Professor 

 Nathorst 3 has quite recently shown that his genus 



1 E. C. Jeffrey, "On the Structure of the Leaf in Cretaceous Pines," 

 Ann. of Bot. vol. xxii. 1908. 



2 Potonie, I.e. p. 317, Fig. 322. The student will find an excellent 

 summary of the geological history of the Coniferae in Professor Potonie's 

 text-book. For the more recent work on the subject see Zeiller, " Les 

 Progres de la paleobotanique de l'ere des gymnospermes," I'rogressus Rci 

 Botanicae, Bd. ii.1907. 



3 " Palaobotanische Mitteilungen. 7. Ueber Palissya, Stachyotaxtis, und 

 Palaeotaxus" Kongl. Svenska Vetenskap Akad. Handl. Band xliii. No. 8, 

 Dec. 1908. 



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