228 APPENDIX. 



It should be mentioned that the division of Sonth America into eastern and 



western regions is a very roughone, the main -^^ft ^neT/a^n 

 western and Andine elements from the eastern. Thus Venezuela is r 

 and New Granada western ; but this very arbitrary and artificial boundary does not 

 vitiate the results to the extent that might be supposed, because it is in a measure 

 counteracted by the column enumerating the species common, nominally, to both tne 

 east and the west, the essentially eastern species being thereby largely eliminated torn, 

 the Andine and truly western forms. As might be expected, the "western only are 

 considerably in excess of the " eastern only." The most striking feature in this Table 

 is the large number of species common to South America, but not known to inhabit tne 

 West Indies. 



Extensions into Countries beyond America. 

 Of the 1849 genera of vascular plants represented in Mexico and Central America, 

 787 recnr in some part or parts of the Old World or in the Pacific Islands and of these 

 no fewer than 609 range widely, many of them very widely, leaving only ^178 which are 

 restricted to one country or region outside of America. Of the 12,233 species, 45,4 

 extend beyond America; 337 of them are widely diffused, and the rest, 117 in number, 

 are of comparatively limited range. The general distribution of those of the last cate- 

 gory may be seen by a glance at the Tables, pp. 218, 219, and the special distribution 

 of some of them is of such great interest that it merits setting forth in some detail. 

 Altogether sixty genera and seventeen species are common to America and Asia only, 

 and seventy-four genera and fifty-five species to America and Africa or the African region 



(Mascarene Islands) only. 



In a series of papers on the Statistics of the Flora of the Northern United States, 

 published by Dr. Asa Gray about thirty years ago, he specially considered the relation- 

 ships existing between the vegetation of Eastern North America and Eastern Asia*, 

 and the object of the Table on p. 229 is to show how far these connections extend 



to Mexico. • t -n 



From this Table are excluded all genera which are widely diffused in Asia. It will 

 be seen that seventeen of the genera do not occur in America north of Mexico ; and of 

 the remainder only five occur in western and not in eastern North America, and these 

 chiefly in the south-western part— thus emphasizing Dr. Gray's conclusions, which 

 several botanists have sought to upset. 



* ' American Journal of Science and Arts,' 2nd series, vol. xxii. 1856, p. 217. 



