4 EDWARD W. BERRY 



vocated the probable origin of the modern stipules from basilar 

 leaf lobes. This suggestion was based on the basal lobes of sev- 

 eral early Tertiary species and the occasional occurrence of com- 

 parable lobes in the modern Platanus occidentalis. This sugges- 

 tion while interesting has not met with a ready acceptance. At 

 the time that Ward wrote much less was known of the paleon- 

 tologic history of the genus, especially its earlier manifestations, 

 than is known today. At the present time the major outlines of 

 this history can be sketched in with a good deal of certainty. 



With the dawn of the Eocene, Platanus is abundant in North 

 America, its original home. It would seem that the Eocene wit- 

 nessed the greatest specific differentiation of the genus for no less 

 than sixteen different species have been described. North Amer- 

 ica is still the home of the majority of these but the genus had un- 

 doubtedly spread into Asia and it is exceedingly common in the 

 Arctic regions in the so-called Arctic Miocene which is really much 

 older than Miocene. From these far northern and now boreal 

 lands Platanus has been recorded in Siberia, Greenland, Iceland 

 and Spitzbergen. At this period it appears to have been too warm 

 in low latitudes, for Platanus is absent from the Eocene floras of 

 Southeastern North America where the remains of tropical strand 

 floras are found, and from the South European Eocene. The 

 abundant American species occur for the most part in the low 

 hilly country which marks the site of the present Rocky Moun- 

 tains. From some of these basins, which at that time enjoyed a 

 humid climate and supported a rich fauna and flora, plane-tree 

 leaves nearly two feet in diameter have been collected. The most 

 southern Eocene record in the European area thus far discovered is 

 in deposits interbedded with the basaltic lava flows of this period 

 on the Isle of Mull from which staminate catkins, fruit and 

 leaves have been described as Platanus hebridicus. 



The Oligocene period which succeeds the Eocene was a period 

 of land emergence and dry hot climates. Consequently the local- 

 ities where plane trees may be presumed to have flourished have 

 been regions where their remains failed to become preserved. North 

 America is especially poor in Oligocene plant remains of all 

 kinds and no Olgiocene species of Platanus have been discovered 



