650 AV. TRELEASE FLORA OE CENTRAL AMERICA 



percentage (25) of the species of higher plants, as he understood them, 

 of Saint Thomas and the adjacent Cretaceous Virgin Islands are not 

 found in the Tertiary island Saint Croix, only some 30 miles away, and 

 that only about 11 per cent of the species of Saint Croix occur also in 

 Saint Thomas. As a general fact, it may be stated that those which 

 stop in Saint Croix are endemic or derived from or represented by species 

 of the Lesser Antilles, and of South American affinity or origin, and that 

 those which stop in Saint Thomas, if not endemic, are of North American 

 origin or affinity, with representatives in the Greater Antilles. Here 

 North America does not mean or include, so far as cases are significant, 

 the subtropical or even warm part of the United States, but it is to be 

 understood as referring to the Mexican and Yucatecan floral zones. 



It has been my privilege to become so familiar with the world repre- 

 sentation of a few groups of plants that I may venture to speak of their 

 geographic distribution with some confidence. What I know of them in 

 this tespect may be stated as follows : 



QUERCUS SUGGESTS LACK OF LaND CONNECTION WITH NORTH AMERICA 



The oaks (Querents)- constitute an ancient genus, dating from the Cre- 

 taceous, scarcely changed since the Pleistocene, and apparently going well 

 into the Pliocene essentially in their present specific forms. The genus 

 is world-wide in its distribution in the Northern Hemisphere now. In 

 America it is essentially North American. Only a few oaks now occur in 

 South America — in the Andes of Colombia. These appear to me closely 

 related to certain Costa Eican species, and thus far support the recogni- 

 tion of a subequatorial Andine province comparable with the cisequatorial 

 and Central American provinces with which the West Indies are corre- 

 lated in their flora. If their remains have been identified correctly, a 

 few oaks occurred in Pliocene time in what is now arid equatorial Brazil. 

 I have not seen specimens or illustrations of these, but should have diffi- 

 culty in comparing them, as described, ^\dth existing species or with other 

 Pliocene species of the genus. 



Only one oak, scarcely differentiable from the live-oak of our Gulf 

 States and its equivalent of the Mexican and Central American coastwise 

 region, occurs in western Cuba. This can hardly be regarded otherwise 

 than as an introduction from the north. The live-oaks of this type appear 

 to represent a rather early stock among modern oaks. In the absence of 

 paleontological evidence, it may be unsafe to attempt to say when the 

 live-oak entered Cuba, but evidence is more necessary for the support of 

 a hypothesis that this was in Tertiary times than for my personal view 



