1888.] PROCEEDINGS OF UNITED STATES NATIONAL MUSEUM. 39 



THE PALEONTOLOGIC HISTORY OF THE GENUS PLATANUS. 



BY LESTER F. WARD. 

 (With Plates xvii-xxii.) 



The paleontologic history of the horse and that of a number of other 

 animals has been worked out to considerable satisfaction by zoologists 

 who have traced the lines of descent far back through geologic time 

 and discovered their remote ancestors and many of the intermediate 

 liuks in the phylogenetic chain. But in the vegetable kingdom few ex- 

 amples have presented themselves in which similar studies could be 

 successfully undertaken. The fossil remains are too meager and imper- 

 fect and the affinities too doubtful, as a rule, to warrant any very wide 

 generalizations relative to the genealogical history of plants. The case 

 of the ginkgo tree presents a partial exception, and I once collected 

 some of the evidence of the great antiquity of that singular and now 

 nearly extinct form of plant life.* Our great trees of the Pacific coast 

 {Sequoia) have also begun to attract attention from this point of view, 

 since it has become known that their aicestral remains are abundant 

 throughout the Tertiary and Upper Cretaceous strata of both hemis- 

 pheres. t 



With dicotyledonous plants the cases are still more rare, in conse- 

 quence of the relatively recent appearance and brief geological history 

 of this class. Baron von Ettingshausen has attempted to trace the 

 chestnut tree back to an early ancestor in the Tertiary formation, | 

 and more recently Dr. J. S. Newberry has introduced us to the ances- 

 tors of the tulip tree in.the Cretaceous clays of New Jersey. § 



Equally interesting with this latter, and, as we shall see, possibly 

 allied to it, is the plane tree, or genus Platanus, of which only seven 

 species survive in the present flora of the globe. Five of these seven 

 species are comparatively rare and little known, only two of them being 

 found within the limits of the United States in New Mexico and Cali- 

 fornia. The two well-known species are the oriental plane tree (Plata- 

 nus orientalis), and our abundant sycamore (P. occidentalis). 



Few as are the living representatives of this type of vegetation, it is 

 now known to have played a prominent part in the Tertiary history of 

 the earth, and no less than twenty fossil species have been recognized. 

 The greater part of these aie from North American or Arctic strata, but 



' See Science, Vol. V, June 19, 1883, p. 495. 



tSee Dr. Asa Gray's address as retiring president of the American Association for 

 the Advancement of Science at Dubuque, August, 1872. 

 tSitzb. d. Akad. d. Wiss., Bd. LXV, Abth. I, Wien, 1872, p. 147. 

 $ Bulletin of the Torrey Botanical Club, New York, Vol. XIV, January, 1887, p. 1. 



