NO. 6 PAST CLIMATE OF NORTH POLAR REGION BERRY 21 



France. The oreater limits of cultivated forms is usually not a result 

 of cultivation so much as it is of selecting the species that will grow 

 in a particular environment. In nature the proper species is subject 

 to the historical factor of there having been ancestors in the region 

 or in a region offering access to the particular region. For example our 

 native Calif ornian palm (Neowashingtonia) is a plant of sandy alka- 

 line soils whose range seems to be conditioned by the geologically late 

 submergence of the Colorado Desert area, and to bear no relationship 

 to latitude. In the present tropics certain palms range upward to 

 nearly 10,000 feet, as in the wet parts of the northern Andes 

 (Ceroxylon, Geonoma, etc.). 



The genus Ficus, to which the cultivated fig l)elongs, is one with 

 upwards of 600 existing species of a great variety of habitats, and 

 with probably as many fossil species, extending back to the dawn of 

 the Upper Cretaceous. Various members range well into the temper- 

 ate zone, both geographical and altitudinal. The cultivated fig gener- 

 ally ripens its fruits in Baltimore. I have seen it in the temperate 

 altitudinal zone in Bolivia, and Weberbauer' records an altitudinal 

 range for it through 8,255 feet in Peru. 



Cinnamomum is the genus to certain members of which the names 

 cinnamon and camphor trees are applied. The genus is large and 

 ranges from the Upper Cretaceous to the present. Although the ma- 

 jority of existing species are confined to the tropics some extend for 

 considerable distances into the Temperate Zone, in fact the com- 

 mercial supply of camphor comes in large part from Formosa and 

 Japan, and the tree is hardy in the southern parts of the latter country. 

 Introduced into Florida it has been widely seeded l)y birds and is 

 perfectly hardy throughout that state. 



Zizyphus is a large genus also going back to the Upper Cretaceous, 

 whose present center of population is southern Asia and the Sunda 

 Islands. The new world species are practically confined to^ the tropics, 

 but in the old world there are distinctly temperate species in southern 

 Europe and eastern Asia. It has run wild in Louisiana, and charac- 

 teristic fruits occur in the Pleistocene of the Atlantic coastal plain as 

 far north as Long Branch, New Jersey. Obviously as a fossil. 

 Zizyphus entirely lacks a tropical significance. 



A third source of error is the common assumption that because a 

 particular type of plant has its home in the equatorial zone it is neces- 

 sarily a tropical plant. The type most frequently alluded to in fossil 

 Arctic floras as indicative of a once tropical climate is the tree ferns. 

 the term embracing a variety of species in several genera. 



* Weberbauer, A., Archiv. Asoc. Peruiana Progreso Cicncia, tomo 2, p. 60, 1922. 



