THE SWEET OR RED GUM AND WITCH HAZEL 185 



throughout the Northern Hemisphere. The same comment apphes 

 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 an- 

 cestral gums of three or more miUion years ago and all of their 

 numerous descendants are so hke the sweet gimis of today. They 

 had the same palmately lobed and variable leaves with finely 

 toothed margins, and this resemblance extends even to the consist- 

 ency 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 Pleistocene 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 occurs 

 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 imperfection 

 of the geological record that the only known Ohgocene species 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 Ohgocene history 

 of Asia and that in North America the Ohgocene 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 fortu- 

 nately are not so chary with their evidence. About 9 species of 

 sweet gum are recorded from Miocene rocks, most of them sur- 



