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10 UNITED STATES AND MEXICAN BOUNDARY. 



lower portion of the Rio Grande, we liave the suh-tropical character of its vegetation Indicated 

 by the presence of the arborescent palms of the ^^ tierra caliente/' we have at the same time the 

 Texas live-oat, the type of a more northern flora. This region has been more thoroughly 

 explored by A. F. Schott, esq^., whose observations upon its botany and other natural features 

 will be found in a separate memoir. 



UPPER MARITIME BELT. 



To the lower belt, which has an uniform alluvial soil, and is more or less influenced by its 

 vicinity to salt water, succeeds rolling prairies, underlaid by cretaceous rocks, which now for 



first time annear. though more 



from 



alluvial deposits. This division includes, as we have already noticed, the most habitable parts 

 of Texas, through which run the numerous rivers which empty into the Grulf of Mexico. Here 

 we find rich cotton lands, and an abundance of trees, including species of oak^ hickory, ash, 



elm 



The 



open prairies are densely covered with luxuriant grasses, and have a rich and varied flora, 

 which has been well explored by the early labors of Drummond, and later by those of Linct- 

 heimer and Wright. Upon the southern portion of the Rio Grande, where there is a higher 

 temperature, united with greater aridity of the soil, a vegetation of q^uite a different character 

 appears ; we have here the dense growth of ^' chapparral,'' which is so peculiar to this region. 



The -plants which make 



mass 



different 



species of mimosa and acacia^ with the well known mezq^uit and other forms, most of which are 



armed with hooked thorn s, and make up a jungle which is almost impenetrable. 



The botany of this region is too well known, from various published accounts, to require 

 further details in this place. 



VEGETATION OP THE CRETACEOUS FORMATION. 



As the geological formation becomes more exclusively cretaceous the vegetation assumes a 

 peculiar character, and is made up of species which are rarely found elsewhere. The shrubbery 



of this 



amonsr which are Berheris 



trifoliolafay Fihus micrqphyllaj Forliera angustifolia y Diospyros Texana^ RoeherUnia spinosa^ 

 AdolpMa infestay MicrorJiamnus ericoideSy and AcanfJioeeltis ^ a new genus of Engelmann, allied 

 to Celtis, Along the margins of the usually dry water courses the dwarf walnut {Juglans 

 rupestris) and Fallugia jparadoxa are constantly found. 



The perennial herbaceous plants of this district are numerous. The rocky ledges produce in 

 their crevices various species of LajpJiamia and the scarlet flowered Pentstemon Grahamii, Several 

 examples of the large tropical family of Malpighiacem are found here, among them GalpJiimia 



linifolia^ Aspicaiya hyssojpifoli 



A Janusia gracilis. Cacti are numerous, and include 

 mammillarias, and numerous species of cereus. The 



Lycopodium dendrolohium grows upon the perpendicular faces of the limestone rocks. This 

 plant commonly called ^^rock rose/' is remarkable \, ' *^ hygrometric qualities of its fronds, 

 which are usually rolled up so that the plant '^rms a dry ball, which expands under the 



moi 



Cheilanthes 



Ft 



/> 



'^d here. 



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