140 APPENDIX. 



tracts the dull foliage of the creosote-bush (Larrea mexicana), the long thorny wands 

 of the Fouquieria, the palm-like Yucca, and the crimson-flowered and spine-armed 

 Cereus." 



The flora of the lower maritime districts of the Rio Grande presents no feature of 

 special interest beyond the fact that it is a mixture of tropical and subtropical forms. 

 This is succeeded by rolling prairies underlaid by cretaceous rocks, abounding in trees, 

 including species of oak, hickory, ash, elm, walnut, cypress, &c, with an exceedingly 

 rich undergrowth of vines and other shrubs. The open prairies are densely covered 

 with luxuriant grasses and a rich and varied herbaceous flora. On the southern portion 

 of the Rio Grande, where there is a higher temperature, united with great aridity of 

 soil, a vegetation of quite a different character appears, chiefly the dense " chaparral," 

 consisting of various species of mimosa, acacia, the mesquit (Prosopis), and other 

 shrubs, mostly armed with hooked thorns and forming an almost impenetrable jungle. 

 Higher up, where the cretaceous rocks come more to the surface, new forms appear, 

 peculiar to this extensive region. The shrubbery is a continuous succession of the 

 same species, prominent among them Berheris trifoliata, Rhus microphylla, Porliera 

 angustifolia, Diospyros texana, Koeberlinia spinosa, Adolphia infesta, Microrhamnus 

 tiricoides, and Celtis pallida*. Along the margins of the usually dry watercourses the 

 dwarf Juglans rupestris and Fallugia paradoxa are constantly found. The crevices of 

 the rocky ledges produce various species of Laphamia and the scarlet-flowered Pent- 

 stemon grahami. Several members of the chiefly tropical Malpighiacese are character- 

 istic of this region, among them Galphimia linifolia, Aspicarpa hyssopifolia, and Janusia 

 gracilis. Cactacese are numerous, especially of the genera Opuntia, Mamillaria, and 

 Cereus, and the curious hygrometric species of Selaginella grow on the perpendicular 

 faces of the limestone rocks, together with ferns of the genera Cheilanthes, Pellcea, 

 and Notholcena. A small species of Agave with prickly leaves is very abundant and 

 troublesome to the traveller. The tablelands and valleys are usually covered with 

 4t grama grass " (Bouteloua), with frequent clumps of Dasylirion. Various interesting 

 Nyctaginese, of the genera Acleisanthes and Selinocarpus &c, are noteworthy; and 

 conspicuous among annuals are several species of Mentzelia, Pedis, Hymenatherum, 

 the pretty Eucnide lobata, &c. ; but there are so many equally abundant that it is 

 difficult to designate any as characteristic of the cretaceous district. The higher 

 alluvial tracts, forming the basin plains, produce species of more northern types, 

 such as (Enothera, Gaura, Biddellia, and Polygala, associated with Zinnia, Peganum 

 mexicanum, and Peteria scoparia. A coarse grass, which presents a uniform dead 

 brown colour throughout the greater part of the year, clothes the depressions in this 

 alluvial region ; and the deep recesses and shaded valleys shelter Quercus emoryi and 



* Here, as in a few other instances, the name employed by Dr. Parry has not been published, and we have 

 substituted what we believe to be the correct one. 



