94 TREE ANCESTORS 



of poplars, several of which are very close to, if not identical with, 

 still existing European forms such as the European aspen, the 

 silver poplar and its downy leafed ally. They are found during 

 this period from Asia Minor to Spain, but there are no known Ameri- 

 can records, since tliis country has unfortunately yielded scarcely 

 any Pliocene plants. 



The Pleistocene or Glacial period is always of particular interest 

 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 uniformity 

 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 2 

 of the 10 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 Denmark, 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 Tacama- 

 hac, and the large toothed aspen, have been found in the Interglacial 

 beds of the Don Valley 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 

 virile 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 Nor- 

 dic race was being evolved. Both willows and poplars must have 

 been familiar and useful plants to the Neolithic men that evolved 



