253:10: 05. 05. SgNITED STATES AND MEXICAN BOUNDARY. 2222227 
— lower portion of the Rio Grande, we have the sub-tropical character of its vegetation indicated 
22222. by the presence of the arborescent palms of the ‘‘ tierra caliente," we have at the same time the 
: 5 Texas live-oak, the type of a more northern flora. This region has been more thoroughly 
х ri ‘explored by A. F. Schott, esq., whose observations upon its botany and other natural features : 
a . will be found in a separate memoir. 
UPPER MARITIME BELT. 
2 im Е То the lower belt, which has an uniform alluvial soil, and is more or less influenced by its 
Е - :Vicinity to salt water, succeeds rolling prairies, underlaid by cretaceous rocks, which now for 
©. the first time appear, though more or less hidden from view by a thick layer of erratic and 
Эр B = ‘alluvial deposits. This division includes, as we have already noticed, the most habitable parts 
Er = of Texas, through which run the numerous rivers which empty into the Gulf of Mexico. Here 
E 2 we find rich cotton lands, and an abundance of trees, including species of oak, hickory, ash, 
.. elm, walnut, cypress, &c., with an exceedingly rich undergrowth of vines and shrubbery. The 
_.. open prairies are densely covered with luxuriant grasses, and have a rich and varied flora, 
Эн which has been well explored Бу the early labors of Drummond, and later by those of Linct- 
x heimer and Wright. Upon the southern portion of the Rio Grande, where there is a higher 
si .temperature, united with greater aridity of the soil, a vegetation of quite a different character 
: ёс appears; we have here the dense growth of ** chapparral," which is so peculiar to this region. 
| 22 The plants which make up the thick шавв of shrubbery known Бу this name are different 
E E HES species of mimosa and acacia, with the well known mezquit and other forms, most of which are 
. armed with hooked thorns, and make up a jungle which is almost impenetrable. 
224 The botany of this region is too well known, from various published accounts, to require - 
- i =>. further details in this place. | 
VEGETATION ОЕ 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 | 3 
ume of this region presents a continuous succession of the same forms, among which are Berberis . 
pu. trifoliolata, Rhus microphylla, Porliera angustifolia, Diospyros Texana, Roeberlinia spinosa, 
22 Adolphia infesta, Microrhamnus ericoides, and Acanthoceltis, a new genus of Engelmann, allied 
to Celtis, Along the margins of the usually dry water courses the dwarf walnut (Juglans 
rupestris) and Fallugia paradoxa are constantly found. 
_ The perennial herbaceous plants of this district are numerous. The rocky ledges produce in 
^. their crevices various species of Laphamia and the scarlet flowered Pentstemon Grahamii, Several 
223 = examples of the large tropical family of Malpighiacee are found here, among them Galphimia 
` `- linifolia, Aspicarpa hyssopifolia, and Janusia gracilis. Cacti are numerous, and include among 
the forms here presented opuntias, mammillarias, and numerous species of cereus. The curious 
: - Lycopodium dendrolobium grows upon the perpendicular faces of the limestone rocks. This 
`. plant commonly called “rock rose,” is remarkable for the hygrometric qualities of its fronds, 
. which are usually rolled up so that the plant forms a dry ball, which expands under the 
influence of moisture, and then appears fresh and vigorous. Several new species of Cheilanthes, 
es iris i зэв her certe of ferns are в found hie: 
