330 ANNUAL EEPORT SMITHSONIAN INSTITUTION, 1913. 



THE GENUS PTEROCARYA. 



The genus Pterocarya Avas described by Kimth in 1824. It is made 

 up of three or four species with very circumscribed ranges. The 

 type Pterocar-ya caucaslca A. Meyer {P. fraxinifolia Spach.) at 

 present is confined to a limited area in trans-Caucasus, while another 

 species occurs in northern China and one or two in Japan, as shown 

 in a greatly exaggerated way in the solid black areas on figure 4. 



The determination of the fossil species from their leaves is beset 

 with difficulties, but the fruits are perfectly characteristic and have 

 been found in a number of instances. 



The oldest known fossil species is recorded from the Tertiary of 

 Colorado, and while the American material that can be referred to 

 this genus is not abundant at any period the genus undoubtedly 

 occurred on this continent during the later Tertiary. One record is 

 from deposits as late as the early Pleistocene, but this is not based 

 upon positively identified material. 



In Europe the records of Pterocarya commence with the Oli- 

 gocene. The Tertiary species are numerous and widespread, the 

 abundant Pterocarya denticulata Heer being found from Bohemia 

 and Transylvania through Germany, Switzerland, and England 

 northward to western Greenland. This widespread species which 

 continues unabated throughout the Pliocene period is thought to be 

 the direct ancestor of the existing Pterocarya caucaslca. There are 

 at least five additional Miocene species. 



The Pliocene species are numerous and abundant, and are found 

 all over southern Europe, being especially common along the elevated 

 shores of the extended Mediterranean Sea, in the plateau region of 

 central France, and in the Apennines of Italy. The still existing 

 Pterocarya caucaslca makes its appearance in the plateau region of 

 central France at this time vv^here it is represented by both leaves and 

 the characteristic fruits. It still grew in Netherlands in the early 

 Pleistocene, according to Dubois, but was apparently exterminated 

 during the glacial period. It is also known from the Altai Mountains 

 of Central Asia in deposits of this age. In figure 4 the known range 

 of the fossil species is shown by vertical lining. It seems obvious 

 from the distribution of the ancestral forms and the very circum- 

 scribed range of the few living descendants that the genus is ap- 

 proaching extinction. 



THE GENUS PL.\TYCARYA. 



The genus Platycarya was characterized by Siebold and Zuccarini, 

 who have described so many oriental plants. It is a monotypic genus ; 

 that is to say, it contains a single existing species, which was the 

 basis of the genus Fortunaea of Lindley. This single species is a 



