134 TREE ANCESTORS 



their oaks and there are several species in tropical Asia and the 

 East Indies as far as New Guinea. 



Although so abundant at the present time the oaks represent a 

 very old type of tree, this would be inferred from their present 

 distribution even though nothing were known of their geological 

 history. Considerable of this ancestral history is known, however, 

 but not in enough detail to do more than sketch its more general 

 outlines. Nor is the information about the existing oaks complete 

 enough to aid greatly in an attempt to outhne the past migrations 

 and evolution of the various forms. DeCandolle's monograph of 

 the existing oaks published in 1864 enumerated 281 species. Since 

 that date much has been learned about oaks in general and much 

 more about the maze of species inhabiting the uplands of Mexico 

 and Central America. In a recent publication Trelease recognizes 

 354 species in America alone so that there must be about 500 

 existing species in the present floras of the world. 



Both Saporta and Ettingshausen have sought to untangle the 

 web of distribution and the geological history of the oaks, but it 

 must be confessed with rather indifferent success. Explanation 

 must still wait upon lagging information, and the present attempt 

 must be considered one of generalities rather than of details. A 

 great many fossil leaves have been described as oaks, but a large 

 number of these have no claim to such a relationship. The problem 

 of identification of oak-like leaves, particularly in the mixed floras 

 of the Upper Cretaceous and Eocene periods is most difficult of 

 solution. When the botanist compares these fossil leaves with 

 only those of the familiar temperate trees he is frequently misled. 

 For example, supposed oaks in the lower Eocene floras of our 

 southern states have been found to represent an entirely different 

 family of plants, the Dilleniaceae, at present not found in the United 

 States. Similarly several oaks were described from PHocene 

 deposits in the state of Bahia, Brazil, which if authentic would 

 represent a remarkable extension of their known range. I have not 

 seen the actual specimens upon which Baron Ettingshausen based 

 these determinations, but I have examined large collections from the 

 same outcrop from which his specimens came, and these represent 



