472 PROCEEDINGS OF UNITED STATES NATIONAL MUSEUM. [1885. 



These observations testify to the remarkable influence of a few degrees 

 of heat in the moisture of the subsoil upon early vernal vegetation. 



From Presidio one sees a lofty mountain to the southeast, Siena 

 Eica, 9,000 feet or more in altitude, probably the highest in the State 

 of Chihuahua. Its summit is covered with Nut Pine of large size (or 

 its Mexican kin, Pinus cembroides), and its slopes with Quercus grisea 

 (Gray Oak) and Arbutus Xalapensis. 



Below Presidio the river enters a series of deep canons not yet 

 thoroughly explored. Vegetation within them is scant, sometimes 

 entirely absent. Two rare and pretty shrubs, Coicania ericccfolia (redis- 

 covered by me on Tornillo Creek) and Emory a suaveolens, were fouud 

 hereabout by the botanist of the Boundary Survey. Below the Bofecillos 

 Mountains, on gravelly mesas, the Eriogonum Havardi, Watson, is con- 

 spicuous with its semi-globular masses of leaves from which spring many 

 slender, diverging stems. With it, but much rarer, was found a new 

 species, E. suffruticosum, Watson. In the canon leading to the San Carlos 

 Crossing I rediscovered the Acacia Schottii, apparently at the identical 

 place where first seen by Dr. Parry. In the same canon were collected 

 a new species of Boerhaavia {B. bracteosa, Watson), the pretty Boachea 

 liaifolia, the rare Mimosa fragrans, and, nearer the river, a giant form of 

 Acacia Jilicina, 6 to 8 feet high, forming a dense thicket. 



Opposite the mouth of the Tarlinga,the Eio Grande issues from the 

 Great Canon through a narrow chasm into which one may advance, 

 creeping under the overhanging walls, nearly half a mile. Here Salvia 

 Menryi and Kama undulatum are common. 



Near the mouth of the Tarlinga, on low sand ba Vi was fouud, with 

 ripe and excellent fruit, the Watermelon (CitruUus vulgaris), which has 

 become extensively naturalized in Western Texas. 



Growing on the immediate shore, and first observed as a native plant 

 north of the Kio Grande, is the beautiful Tobacco-Shrub (Xicotiana 

 glauca), and on neighboring gypseous hills that rare and curious shrub 

 Salazaria Mexicana. Farther down, in foot-hills nearly opposite San 

 Vicente, was collected a new species of a Mexican genus, Brongniartia 

 minutifolia, Watson. 



Del Rio is a promising agricultural village, where, among other fruits, 

 delicious peaches are raised. From this point almost down to Eagle 

 Pass the fertile and wide valley seems well adapted to farming. Settle- 

 ments occupy the several creeks watering it. 



At Eagle Pass, distant 495 miles from the mouth of the river, altitude 

 1,460 feet, the general aspect of the vegetation remains the same but 

 a close examination reveals changes. The Bear Grass has disappeared, 

 and the giant Yucca baccata is dwarfed to a mere tuft of leaves. Acacia 

 Greggii and constricta of the gravelly mesas of Presidio are here replaced 

 by Acacia amentacea, Berlandieri, Coulter i, and Wrightii. The Mezquit 

 is as common as ever, shading the parade ground of old Fort Duncan, 

 ts gnarled branches often loaded with thrifty bunches of Mistletoe 



