480 PROCEEDINGS OF UNITED STATES NATIONAL MUSEUM. [1885. 



traversed them without enduring special hardships or privations. They 

 have but few sand belts and grass seldom fails ; the only apprehension 

 in dry seasons is about potable water. 



The Southern Plains are much more barren ; they include the noto- 

 rious Saud Hills and large arenaceous sterile areas entirely destitute of 

 surface water. No one can venture over them without running serious 

 risk from scarcity of water, or sand-storms. 



Big Spring is on the southeastern edge of the plains. This very re- 

 markable spring, by far the most important between the Colorado and 

 the Pecos, issues from under a cliff at the head of a ravine. In this 

 as in the many other ravines running into the dry arroyo called Giraud's 

 Creek, there is more or less arborescent vegetation. Hackberry and 

 Willow predominate ; Red Cedar and Gray Oak are common on the hills 

 but neither of useful size. Conspicuous on the slopes are the tall Eri- 

 ogonum alatum, the humbler E. Jamesii, the bushy Hymenatherum acero- 

 sum, and on the plains below the showy Aplopappus ciliatus and Eryngium 

 Leavenworthii. One or two species of Aristida, Bouteloua, Sporobolus, 

 and Triodia are the ordinary grasses. 



For several miles west of Big Spring there is a thick growth of shrubby 

 Mezquit; it becomes gradually thinner and disappears about 18 miles 

 out. The flat, barren plains show large bald areas ; patches of Panicum 

 obtusum and Brizopyrum spicatum here and there cover the alkaline soil. 



Mustang Spring lies in one of the drains of the Concho, where crossed 

 by the Texas Pacific Eailroad. Here brackish water gravitates into a 

 small basin and is obtained at a depth of a few feet. This basin is 

 covered with Selianthus lenticularis, Aplopappus rubiginosus, Flaveria 



, Bigelovia Wrightii, and Sporobolus airoides. On surrounding 



mesas is a fair amount of Common Grama. 



Following the railroad (past Midway Station) over the level prairie, 

 burned in places by locomotive sparks, I noted the trailing Tribulus 

 maximus, the common weeds Namahispidum and Coldenia hispidissima, 

 the pretty and ephemeral Portulaca pilosa and a homely form of Oeno- 

 thera Greggii with blotched ovate leaves. 



Odessa Station stands in the midst of a prairie district, and as the 

 vegetation hereabout is more or less typical of that of the better parts 

 of the Staked Plains I shall briefly describe it. Bushes are scant and 

 dwarfed ; they consist of Mezquit only 1 or 2 feet high, a very slender 

 form of Yucca angustifolia, the Creosote-bush (Larrea Mexicana), the Lote- 

 bush (Zizyphus obtmifolius), Canatilla (Ephedra trifurca). The most 

 common non-ligneous plants are : 



Verbena canescens and bracteosa. 



Nyctaginia capitata. 



Allionia incarnata. 



Solanum elwagnifolium. 



Physalis hederwfolia, and mollis, var. cinerascens. 



Croton corymbulosus and Texensis. 



