28 CONTRIBUTIONS TO PAL^ONTOLOGY 



relationships have been estabhshed between fossil forms and hving genera and 

 species, it is often difficult to determine from either Uterature or herbarium speci- 

 mens the precise distribution and climatic requirements of the hving relatives. 

 This appUes particularly to subtropical and tropical forms. 



To anyone familiar with temperate forests of either hemisphere, it is apparent 

 that the lower Medicine Bow flora is distinctly not a cool temperate assemblage. 

 The absence of t^qDicaUy cool temperate genera is striking. Rather than rely on 

 such negative evidence, I would emphasize that the majority of the lower Medicine 

 Bow species which are comparable to hving forms show close resemblances to 

 genera now hving in warm temperate and subtropical forests, as shown in table 3. 

 Fossil species which have not been found comparable to anj^ modern leaves have 

 been omitted from this hst. 



The distribution of modern correlatives and alternatives shown in table 3 

 indicates that only a small number of genera are found in cool temperate assem- 

 blages. With no exceptions, moreover, these few genera are of non-restricted 

 distribution, extending in all cases into warm temperate or subtropical associations. 

 Some of them, such as Nyssa, Magnolia, Drimys, and Viburnum are in fact more 

 numerous and widespread in warmer forests, and extend into the cool temperate 

 regions only in a Umited number or a Umited area. The large number of generic 

 correlatives of warm temperate and subtropical forests clearly substantiates the 

 inferences based upon the characters of leaves of the Medicine Bow species. The 

 relatively large number of tropical genera represented does not imply close relation- 

 ship to lowland tropical forests, since none of these genera is restricted to such 

 habitats; aU of them are equaUy weU developed in subtropical associations, and 

 may range into the warm temperate. 



A consideration of several individual famUies whose presence is weU estab- 

 Ushed in the Medicine Bow flora adds weight to the cUmatic inferences based upon 

 leaf characters and the aspect of the flora as a whole. Most convincing, perhaps, 

 is the famUy Palmse, represented by Sabalites eocenica and S. montana. Although 

 the actual genus to which these species belong may be in doubt, their reference to 

 the palm famUy cannot be questioned. In the Uving flora, pahns are typicaUy 

 tropical and subtropical in distribution. Their most northerly representatives 

 range only into the warm temperate lowlands of the Atlantic Coast {Sabal pabnetto 

 and Serenoa serrulata), CaUfornia {Washingtonia filamentosa), southern Europe 

 (Chamcerops humilis), and southern Asia (Chamcerops spp. and Rhapis spp.). 

 The Pandanacese, represented by the fossU species Pandanites corsoni, the Myrta- 

 cese (Myrica torreyi), the DiUeniacese (Rhamnus cleburni), and the Lauraceae 

 {Laurophyllum meeki, Ficus tesselata, Rhamnus salicifolius) are hkewise typicaUy 

 tropical and subtropical famiUes whose modern distribution in temperate forests is 

 restricted to the warm lowlands bordering the subtropics. 



The combined evidence presented from the study of the leaf characters of the 

 Medicine Bow species, the distribution of closely related genera of the flora as a 

 whole, and the climatic requirements of modern famUies which are represented in 

 the fossU flora is consistent throughout in indicating warm temperate to subtropical 



