CHAPTER X 



CONIFEROPHYTES— GINKGOALES 



This order is still represented by one living genus, Ginkgo. Its 

 ancestry can be traced back to the Paleozoic, and, like the cycads, 

 it may be called a living fossil, for it still retains the swimming sperm 

 which characterizes the ferns and which probably characterized all 

 of the Paleozoic seed plants. 



Leaves are abundant in the Permian, and leaves which may be- 

 long to the order, but which may belong to the Cordaitales, were 

 abundant in the Carboniferous. From the Triassic the order de- 

 veloped rapidly and can be traced with confidence, reaching its 

 greatest abundance and widest distribution in the Jurassic; but be- 

 fore the end of the Jurassic, it began to wane, and is now represented 

 by the single genus. Ginkgo. 



EXTESrCT MEMBERS 



As extinct members of this order, aside from Baiera, which all 

 recognize as nearly related to the living Ginkgo, Pilger, in Die 

 naliirlichen Pfianzenfamilien, lists seven genera as more or less prob- 

 ably related, and six more as more or less doubtfully belonging here. 



The living genus, Ginkgo, is not rare in the Liassic, and in the 

 middle Jurassic was abundant and world-wide in its distribution. 

 Several extinct species have been described, but, since they are based 

 principally upon leaves, it seems just as well to put all of them under 

 Ginkgo biloba. Its leaves vary so much with age, position on the tree, 

 and environment, that most, if not all, of the leaf impressions which 

 have tempted taxonomists to make more species could be dupUcated 

 by leaves of the living species. 



Baiera'^^^ was abundant in the lower Permian of Europe and North 

 America. In the Jurassic it was not so abundant as Ginkgo. Im- 

 pressions have been found in the Rhaetic of South Africa. The 

 genus became extinct in the Lower Cretaceous. 



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