SWEET GUM AND WITCH HAZEL 349 



species of Sterculia — a tropical genus of trees that was very com- 

 mon in Upper Cretaceous times throughout the northern hemi- 

 sphere. The same comment applies to an early Eocene form 

 described from France by Watelet, a student of the fossil floras 

 of the Paris Basin. 



The oldest known authentic form is found in the upper Eocene 

 in Greenland, Alaska and Oregon. This hints at the Arctic region 

 as the original home of the genus — a not improbable hypothesis, 

 although one for which the evidence is not conclusive, since the 

 vast and almost unknown expanse of Asia cannot be left out of 

 the reckoning. What is more remarkable is the fact that these 

 ancestral gums of three or more million years ago and all of their 

 numerous descendants are so like the sweet gums of today. 

 They had the same palmately lobed and variable leaves with 

 finely toothed margins, and this resemblance extends even to the 

 consistency of the leaves. Today in our southern rivers the 

 sweet gum leaves are the first to decay when they fall in the water 

 and similarly in the Pliocene river deposits the gum leaves are 

 rarer and nearer dissolution than the leaves of their associates. 

 Judging by their usually fragmentary condition in the older 

 rocks this characteristic was as true then as now. 



Let us emphasize then the first landmark in the history of the 

 sweet gum, namely that the oldest known authentic species oc- 

 curs in the late Eocene of the far north and on our Pacific coast 

 in Oregon and Alaska. 



Following the Eocene is the period of earth history known as 

 the Oligocene, and it is a striking commentary on the imperfec- 

 tion of the geological record that the only known Oligocene spe- 

 cies of gum is recorded from Italy. This is not quite as bad as 

 it seems when it is recalled that we know nothing of the Oligo- 

 cene history of Asia and that in North America the Oligocene 

 was a time of continental mountain basin and plains deposits 

 throughout the west and of tropical marine deposits along the 

 southern coasts, in neither of which are to be found many traces 

 of the terrestrial vegetation of that time. 



The Oligocene was followed by Miocene times and these for- 

 tunately are not so chary with their evidence. About nine spe- 



