150 TREE ANCESTORS 



went back much farther than the geological records indicate is 

 the presence of several elms in the basal Eocene of such widely 

 separated regions as France and Colorado. Presumptively these 

 ancient elms reached these localities from a third and more northern 

 area. None are known, however, from the Upper Cretaceous plant 

 beds of western Greenland where so many ancestral forms have 

 been found, so that we cannot be sure whether the ancestral elms 

 spread to France across an Upper Cretaceous North Atlantic 

 land bridge or whether Asia was their original home and that they 

 spread from that continent southwestward into western Europe 

 and southeastward across the Behring Sea land bridge into the 

 western land mass of North America which was separated at that 

 time from eastern North America by an inland sea. 



Later in Eocene time, with the spreading of the seas and the 

 opening up of the Arctic to a free oceanic circulation from low 

 latitudes, the elms, along with so many of our temperate forest 

 types, spread into the far northern lands, and late Eocene elms 

 are recorded from Colorado, Wyoming, Montana and Oregon 

 northward through British Columbia, where seven species have 

 been found, to Alaska, and across the north Pacific in beds of this 



Fig. 32. Some Recent and Fossil Elms and Hackberries (About § 

 Natural Size) 



1. Ulnius Montana Sm., the Witch Elm, leaf. 2. Fruit. 



3. Ulmus fulva Michx., the Slippery Elm, leaf. 4. Fruit. 



5. Ulmus alata Mich.x., the Winged Elm, leaf. 6. Fruit. 



7. Ulmus plurinervia Unger, a Miocene elm leaf. 8. Fruit. 



9. Ulmus bicornis Unger, a fossil elm fruit. 



10. L7wm5 5ro?nzfi Unger, a Miocene elm fruit. 11. A leaf. 



12. Ulmus longifolia Velen., a Miocene fruit. 



13. Ulmus prisca Unger, another Miocene fruit. 



14. Ulmus Braunii Heer, a Miocene leaf. 



15. Celtis australis L., fruit. 16. Leaf. 



17. Celtis japonica Pr., leaf. 



18. Celtis Hyperionis Unger, a Miocene stone. 



19. Celtis Japcti Unger, a JSIiocene leaf. 



20. Celtis occidentalis L. The American Hackberry, leaves and fruit. 



21. Celtis Bernhardtii Klotzsch, a leaf. 



