EELATIONSHIPS WITH THE ELOEAS OP OTHEE EEGIONS. 223 



EELATIONSHIPS OF THE FLOEA WITH THE FLORAS OF OTHER 



REGIONS. 



Having reviewed the various elements of the vegetation of Mexico and Central 

 America and set forth its general distribution, we are now in a position to deal with 

 the particulars of its relationships to, and connections with, the vegetation of other 

 regions. Without attempting exact definitions of boundaries here, we may repeat that 

 there are three distinct floral provinces within our limits, corresponding very nearly to 

 the political boundaries which we were compelled to adopt on account of the plants of 

 many collections not being localized more precisely. Thus Nicaragua, Costa Rica, and 

 Panama, which may be collectively designated the southern area, constitute a province 

 of the American and West-Indian tropical flora ; and the northern area, comprising 

 Salvador, Honduras, Guatemala, and Mexico, constitutes the Mexican flora. This 

 naturally falls into two provinces, a northern and a southern, the latter including 

 South Mexico and the country southward to the borders of Nicaragua, and the former 

 North Mexico, Western Texas, New Mexico, and Arizona, except the alpine flora, with 

 indefinable extensions into other territories. The abrupt cessation of orchids and other 

 epiphytes, as well as some other classes of plants, coincides so nearly with our rough- 

 and-ready boundary, adopted in ignorance of these circumstances, that there can be no 

 question as to the propriety of separating North and South Mexico in a phyto- 

 geographical disquisition. 



We will first consider the American connections of the vegetation of Mexico and 

 Central America. 



Extensions into eastern and western North America. 



For the purposes of this work eastern North America is the country east of the 

 Mississippi; and Western, the country west of that river. This division was adopted 

 because it was not found practicable to separate the central region from the western. 

 As a matter of fact, the " western " extensions are mainly into the central region. The 

 result of an analytical comparison of the north-eastern and north-western extensions 

 fully bears out the theory of a North Mexican province, as roughly indicated in the 

 preceding paragraph. Thus : — 



Western extensions. Eastern extensions. 



, A ^ 



Genera. Species. 



Dicotyledones 537 990 



Monocotyledones 94 126 



Totals 631 1116 557 552 





x 



^ 



Genera. 



Species. 



449 



389 



108 



163 



