Chapter X 



-195- 



Historical Causes 



But at this very time Liriodendron makes its appearance in Europe, 

 which indicates that there existed a land connection between this con- 

 tinent and America. The earliest Tertiary remains of this plant, which 

 have been referred to the Mexican species, L. Procaccini, are those from 

 the Eocene stage found in England and Iceland. These fossil occur- 



FiG. 3$. — Area of the genus Liriodendron in different 

 geologic periods: i, Cretaceous; 2, Eocene; 3, Miocene, 

 but areas during several geologic epoclis are plotted: 

 bent oval = Miocene; squares = Pliocene; dotted line = 

 Quarternary. The map of the Cretaceous is taken from 

 Wegener, the others have been compiled according to 

 Wegener's data. The geographic network (0°, 30°, 60°) of 

 the respective geologic epochs has been plotted on all three 

 maps according to Wegener's data. (After Sh.\p arenko) . 



rences lie just south of the 30th parallel of those times, which is at 

 approximately the same latitude as the center of the area of this genus 

 during the Cretaceous period. 



During the Miocene stage Liriodendron, represented in all prob- 

 ability by a considerable number of species, greatly extends its range, 



