PERIODICAL LITERATURE 



BOTANY AND ZOOLOGY 



Trelease has recently published two important 

 American papers on American oaks ; one on the ancient oaks 



Oaks of America and the other on the naming of Amer- 



ican hybrid oaks. The purpose in the first of 

 these papers is to bring together the scattered facts relating to fossil 

 American oaks. 



The many species of oak which are now a most striking component 

 of forest vegetation in America and of large economic value are worthy 

 of much attention on the part of silviculturists and dendrologists. A 

 thorough knowledge of living species demands some knowledge of those 

 that existed before our own day. Although a large number of fossil 

 oaks have been described, they have, for the most part, been identified 

 from the impressions of leaf fragments. Only two fossil species appear 

 to be known in fruit. Due to the fragmentary character of fossil ma- 

 terial and the absence of twigs and fruits, many fossils appear to have 

 been called oaks rather because they could be called nothing else than 

 for any other positive reason. 



Early identifications often placed European and American forms to- 

 gether, but at present very few American fossil oaks are considered 

 identical with European species. The earliest appearance of Qnercus 

 is in the Cretaceous, for which 48 species are recognized in the United 

 States and Canada. None of these survive the Cretaceous and none 

 closely resembles existing oaks. Fifty-six species are reported from 

 the Eocene, distributed from Alaska to Mexico. Like those from the 

 Cretaceous, none closely resembles living species. The species for the 

 Miocene, numbering 42, are widely distributed over the United States. 

 These oaks are more closely related to existing species, as shown in the 

 fact that a Miocene oak of California has been considered a variety of 

 an existing species. Otherwise none of the species of Miocene oaks are 

 thought to exist today. The Pleistocene oaks, which occur in glacial 

 and later deposits, are strikingly like existing species and manv are 

 considered identical, while others are believed to be ancestral forms 

 of present species. 



The author has arranged the principal leaf types of American fossil 



185 



