DISTRIBUTION OF VEGETATION IN UNITED STATES. 91 



22. Paired Species of Eastern and Western Ranges, Respectively. 



(Plate 33.) 



Floerkea occidentalis Rydb. 



Floerkea proserpinacoides Willd. 



Trautvetteria grandis Nutt. 



Trautvetteria carolinensis (Walt.) Vail ( = T. palmata Fisch. and Mey.). 



Cebatha diversifolia (DC) Kze. ( = Cocculus diversifolius DC). 



Cebatha Carolina (L.) Britton ( = CoccuIus carolinus (L.) DC)- 



There are a few cases in the flora of the United States in which a 

 genus has two species, one of which is eastern and the other western 

 in range. We have selected the paired species of each of the three 

 genera, Floerkea, Trautvetteria, and Cebatha, with a view to investigating 

 the climatic conditions characteristic of the present separated ranges 

 of these pairs of closely related plants. There is some doubt in the 

 case of the two species of Flcerkia as to their specific distinctness. The 

 two species of Cebatha apparently overlap in central Texas, whereas 

 the other two species are widely separated. 



