202 THE GEOLOGICAL HISTORY OF PLANTS. 



resented by a single species, was in the Cretaceous age 

 much more largely developed, having many species, and 

 those scattered throughout many lands. In the Tertiary 

 age the genus continued to exist, but the species seem to 

 have been reduced to one, which is hardly to be distin- 

 guished from that now living. In many parts of Europe 

 leaves of the tulip-tree have been found, and it extended 

 as far south as Italy. Its presence there was first made 

 known by Unger, in his 6 Synopsis/ page 232, and in his 

 ( Genera et Species/ page 443, where he describes it 

 under the name of Liriodendron procaccinii. The genus 

 has also been noticed in Europe by Massalongo, Heer, and 

 Ettingshausen, and three species have been distinguished. 

 All these are, however, so much like the living species 

 that they should probably be united with it. We here 

 have a striking illustration of the wide distribution of a 

 species which has retained its characters both of fruit and 

 leaf quite unchanged through long migrations and an 

 enormous lapse of time. 



" In Europe the tulip-tree, like many of its American 

 associates, seems to have been destroyed by the cold of 

 the Ice period, the Mediterranean cutting off its retreat, 

 but in America it migrated southward over the southern 

 extension of the continent and returned northward again 

 with the amelioration of the climate." 



Leaves of Liriodendron have been recognised in the 

 Cretaceous of Greenland, though it is now a tree of 

 the warm temperate region, and Lesquereux describes 

 several species from the Dakota group. But the genus 

 has not yet been recognised in the Laramie or in the 

 Upper Cretaceous of British Columbia. In the paper 

 above quoted, Newberry describes three new species 

 from the Amboy clays, one of which he considers iden- 

 tical with a Greenland form referred by Heer to L. 

 MeeTci of the Dakota group. Thus, if all Lesque- 

 reux's species are to be accepted, the genus begins 



