Chapter X 



-191— 



Historical Causes 



vation in the flora of this region of a number of ancient, relic ele- 

 ments. 



Coniferae. — A test of Wegener's theory on the basis of the distri- 

 bution of conifers was made by Studt (1926). The regularity estab- 

 lished by Irmscher as regards the structure of areas was fully 

 confirmed by Stxjdt in the case of the areas of conifers, a study of 

 which led him to the following conclusions. 



The first conifers made their appearance in the Upper Carboniferous 

 and Permian periods. As regards their dispersal, we can, on the basis 

 of paleobotanic data, establish three stages: (i) from the Upper 

 Carboniferous to the Triassic period — dispersal throughout the north 

 temperate zone of Europe and North America; (2) during the Mesozoic 

 era there are formed two centers of distribution of conifers — in the 

 southern hemisphere there are concentrated Araucariaceae and Podo- 

 carpaceae and in the northern Pinaceae and Taxodiaceae and later also 



— •— 7y>s ^'ocG^s cr/^ecr. 

 O TVje /'//ocene ameer 

 # me ^uoter>/70/'y o/^ea. 



Fig. a. — The Eocene-Oligocene, Miocene, Pliocene, and Quarternary areas of Ginkgo 

 adianloides . The geographic network and the shapes of the mainlands are those of the 

 Miocene, (.^fter Shapasenko). 



Taxaceae and Cupressaceae (at this time Europe has an abundance of 

 conifers, exceeding possibly in number even those of North America); 

 (3) the Quaternary period is characterized by the predominance of 

 conifers in North America and eastern Asia and the occurrence of 

 isolated areas in the southern hemisphere. In Europe during the Ice 

 Age a large part of the conifers died, while in North America and 

 eastern Asia, thanks to more favorable conditions, particularly the 

 absence of mountain chains running east and west that would have 

 constituted barriers to the southward spread of vegetation, they were 

 preserved in considerably greater numbers. In these latter regions in 

 post-glacial times there also arose new forms, while Europe remained 

 poor in species of conifers. Consequently, as Irmscher also estab- 

 lished, Europe, which was characterized during the first and second 



