204 TREE ANCESTORS 



We are %vithout information as to whether Cercis came down 

 from the north into both North America and Europe or whether 

 America was its original home and it spread across the land bridge 

 in the region of Behring Sea into Asia and thence into Europe. 

 Personally I favor the interpretation that the vast and paleobotani- 

 cally almost unkno\vn continent of Asia was the original home of 

 the genus from which it spread westward into Europe and eastward 

 across the Behring land bridge into North America. If this is 

 the true story then this migration must have taken place during 

 Upper Cretaceous times even though we have not yet found Cercis 

 in the abundant Upper Cretaceous floras, for it is present in the 

 lower Eocene of our Gulf States and in the middle Eocene of the 

 south of England and a journey from Asia would have required 

 a very long time. 



The Miocene was pre-eminently the period of hardwood forests, 

 and the ancestral Judas-trees seem to have reached the zenith of 

 their differentiation and their most extensive range during these 

 ages that succeeded the OHgocene. Although Asia remains an 

 unknown area we have a glimpse of a small species preserved 

 in the volcanic ash beds of the Florissant lake basin in the heart of 

 the Colorado Rockies, and a second species in Nevada. No less 

 than 5 species are already known from Miocene Europe, where 

 they are represented as fossils by both leaves and pods. It is 

 especially interesting to note that one of these from the late Miocene 

 of Italy and another closely related form of the same age in France 

 are directly ancestral to the existing European Judas-tree, while 

 a second French species {Cercis ameliae Saporta) from the older 

 Miocene of France seems to have been the ancestor of the existing 

 Cercis japonica Siebold of eastern Asia. There is little direct 

 evidence of the Judas-tree during the succeeding Ph'ocene times. 

 Since it occurs both before and after the Pliocene in North America 

 it must have been present at that time. In Europe a single 

 Pliocene species is known from France. 



As practically everyone knows, the Pleistocene, which succeeded 

 the Pliocene, was a time of continental ice sheets or glaciers, which 

 played havoc with the floras and faunas, particularly in Europe 



