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198 



TUE GEOLOGICAL HISTORY OF PLANTS. 



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(birch) is representor! by a few species, and specimens of 

 its peculiar bark are also common. Alnus (alder) ap- 

 pears in one species at least. The genus Platanus (Fig. 

 71), that of the plane-trees, represented at present by one 



Fio. 71. — Platanus nobilis. Newberry, variety baailobata. Laramie. 



Much reduced. 



European and one American species, has several species 

 in the Cretaceous, though the plane-trees seem to culmi- 

 nate in the early part of the succeeding Eocene, where 

 there are several species with immense leaves. The large 



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