78 TREE ANCESTORS 



existing South American species. It is readily apparent from this 

 map that the modern species with their disconnected distribution 

 represent the segregated remnants of a once worid wide distribu- 

 tion, and that the Glacial period or Ice Age was as unimportant an 

 incident in their history in North America, where there were no 

 mountain or water barriers to cut ofif their retreat before the ice, 

 as it was a tragic event in Europe, where from Gibraltar to the 

 Caspian a succession of sea and mountains blocked their retreat 

 to the southward greatly restricting the range of Juglans regia, 

 and altogether exterminating one or two additional species of 

 walnut, as well as the European hickories and a host oi other trees. 



The other members of this ancient and noble family are no longer 

 present in our American forests, but some of them once Hved here 

 in the distant past, and I have introduced a map of their present 

 and past distribution to show how imperfect is our knowledge if 

 it be confined merely to the present, and to illustrate the principle 

 that closely related trees, or any other kinds of organisms for that 

 matter, which are now found on perhaps opposite sides of the globe, 

 are descended from common ancestors which once spread over the 

 intervening lands. 



These members of the family now extinct in temperate North 

 America are Platycarya, a small tree of Japan and northern China 



Fig. 16. Some Fossil Leaves and Nuts of Walnut (About ^ 

 Natural Size) 



1. Juglans arctica Heer from the Upper Cretaceous of Western Greenland. 



2. Juglans schimperi Lesquereux from the Eocene of Louisiana. 



3. Juglans rugosa Lesquereux from the Eocene of Wyoming. 



4. Juglans acuminata Alex. Braun from the Miocene of Switzerland. 



5. Juglans paviaefolia Gaudin from the Pliocene of Italy. 



6. Juglans sieboldiana Maximowicz, nut from the late Tertiary of Japan. 



7. Juglans cinerea Linne, nut from the Pleistocene of Aldan River, central 

 Siberia. 



8. Juglans cinerea Linne var mucronata, nut from the upper Pliocene 

 lower Main valley, Germany. 



9a, 9b. Juglans cinerera Linne var tnucronata, surface and interior view of a 

 nut from the Wetterau lignites of Germany. 



