THE ELOEA OF NOETH MEXICO. 139 



Noeth Mexico. 



It is difficult to determine, even approximately, the area of Mexico ; but for the 

 purposes of geographical, botany this is of comparatively little importance, for it is 

 notorious how large a proportion of the whole flora of a country is contained within a 

 small space of it. North Mexico, however, is the largest of our seven divisions, having, 

 as here limited, its southern boundary conterminous with the southern boundaries of 

 Sinaloa, Durango, Zacatecas, and San Luis Potosi, extending altogether through about 

 eleven degrees of latitude. Mazatlan, on the western coast, is counted to North Mexico ; 

 and Tampico, on the eastern coast, to South Mexico. This arbitrary boundary, as the 

 sequel will demonstrate, coincides, as nearly as any that could be proposed from the 

 available data, with a decided change in the vegetation, the most marked feature of 

 which is the abrupt northern limit of epiphytal phanerogamic vegetation. Indeed, 

 excepting the littoral belt, one might say that purely tropical types do not extend into 

 North Mexico, although a considerable portion of it is situated within the tropics ; and 

 this is not wholly due to elevation, but rather to climatal conditions. Much of the 

 country is high tableland, yet there are no lofty peaks such as characterize South 

 Mexico. Tula is at 4000 feet, the town of San Luis Potosi at 6170, Zacatecas at 8000, 

 Durango at 6700, and La Cumbre, in the State of Durango, rises to a height of 10,500 

 feet, the highest point, we believe, in North Mexico. Every one of the States of North 

 Mexico has been, more or less, botanically explored, and, although much remains to 

 be done, the general character of the flora is very well known. What this is may be 

 gathered from that which immediately follows, the geographical tables, and the para- 

 graphs on the general distribution of the prominent and peculiar natural orders, the 

 essence of which will be summed up and commented upon at the end of this essay. 

 The eastern States have been more thoroughly investigated than the western, yet there 

 is nothing published on the aspects and composition of the vegetation which merits 

 reproducing here. Parry and Palmer and Pringle's recent explorations have added 

 very largely to the number of species, both new ones and others previously known only 

 from north of the Rio Grande ; but remarkably few new generic types were discovered. 

 Unfortunately, these gentlemen have hitherto published nothing on the aspects and 

 composition of the vegetation. There is, however, Dr. Parry's sketch of the more 

 striking features of the vegetation of the country on the boundary-line between the 

 United States and Mexico*, from which we glean the following particulars. Inci- 

 dentally he remarks :— " The observer, a little perplexed by a great variety or gradual 

 blending of forms, involuntarily associates particular localities with the predominating 

 and characteristic vegetable productions. Thus one who has ever traversed the desert 

 tablelands of the Upper Rio Grande will not fail to unite in his recollection of these 



* Introduction to Torre/a Botany of the Survey, forming part of Major Emory's Eeport. 



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