HISTORY OF THE WILLOWS AND POPLARS 27 



aspen, the silver poplar and its downj- leafed ally. They are 

 found during this period from Asia ]Minor to Spain, but there 

 are no known American records, since this countrj^ has un- 

 fortunately yielded scarcely any Pliocene plants. 



The Pleistocene or Glacial period is always of particular inter- 

 est to students of plant history and distribution since the presence 

 of continental ice sheets and the complex physical conditions 

 which their presence brought about played havoc with the uni- 

 formity of development and distribution of the noble races of 

 both animals and plants that had been flourishing for so many 

 thousands of years throughout the Northern Hemisphere. 



Poplars are represented in the Pleistocene deposits of Europe 

 and America by wood, leaves, bud-scales and catkins. Only 

 two of the ten species recorded from these deposits are extinct 

 and these are both from the earlier Pleistocene of Maryland 

 and are very similar to existing forms. In Europe the black 

 poplar is recorded from Italy; the downy white poplar has been 

 found in both England and France; and the European quaking 

 aspen occurs in peat deposits at a number of localities in Den- 

 mark, Germany, northern Italy, etc. In America the so-called 

 necklace poplar (Populus deltoides) has been found in river 

 terrace deposits in Alabama and western Kentucky, and the 

 balsam poplar or Tacamahac, and the large toothed aspen, have 

 been found in the Interglacial beds of the Don vaUey in Ontario 

 and the former has also been found in the blue clays of Maine. 



Thus we see that while the life span of both willows and poplars 

 is much shorter than that of most of our forest trees, the stock 

 is a ^drile one and the race an ancient one. While neither have 

 been objects of veneration or worship like the oaks or ginkgoes, 

 or of surpassing utility like so many of our forest trees, both were 

 the associates of our remote ancestors of the Old Stone Age 

 when the last ice sheets were retreating from northern Europe 

 and the Nordic race was being evolved. Both willows and 

 poplars must have been famiUar and useful plants to the Neolithic 

 men that evolved the so-caUed Robenhausian culture of the 

 Swiss lake dwellers (7000-5000 B.C.), the remains of whose 

 d"v^'elhngs, built on piles and found so abundantly throughout 



