1885.] PROCEEDINGS OF UNITED STATES NATIONAL MUSEUM. 471 



More conspicuous and interesting herbs are — 

 On the bottom : 



Collomia longiflora. 



Tribulus grandiflorus. 



Martynia althecefolia. 



Oenothera triloba and pinnatifida. 



Argemone hispida. 



Hoffmanseggia stricta. 



Sphceralcea angustifolia. 



Tetraclea Coulteri. 



Lepidium alyssoides. 



Philibertia cynanchoides and linearis. 

 On the mesas : 



Talinum aurantiacum. 



Lceselia Havardi, Gray. 



Cassia bauhinioides. 



Mentzelia multiflora. 



Talinopsis frutescens. 



Baileya multiradiata. 



Biddellia tagetina. 

 The coarse " Maton " grass (Sporobolus Wrightii), on which many of 

 the native ponies feed in winter, occupies large portions of the open bot- 

 tom. The grazing is very poor "in the valley and on the low mesas 5 it 

 is only in the foothills that we find nutritive Grasses, principally 

 Bouteloua oligostachya and polystachya, Cathestechum erectum, Aristida 

 purpurea. 



Here the Rio Grande receives its largest affluent, the Eio Conchas, 

 having its source nearly due south in the Sierra Madre of Chihuahua. 

 The valley of this fine river is very fertile, and, under irrigation, pro- 

 duces abundant cereals, vegetables, and fruits, on which subsist many 

 towns and villages from Presidio del Norte to Chihuahua. 



An excursion of about 40 miles through and beyond the Canon of the 

 Conchas did not reveal any notable change. The country, outside of 

 the river bottom, is a hopeless desert extending to the very mountains 

 surrounding the City of Chihuahua. In this desert we found a flourish- 

 ing Sotol -mescal factory, the favorite alcoholic beverage of frontier 

 Mexicans, made from the Sotol or Bear- Grass. 



On February 14, 1881, I was surprised to see the Cottonwood on the 

 Conchas already quite green, while those of the Eio del Norte, on the 

 other side of the dividing ridge were still a bare, blackish mass. I 

 subsequently ascertained that the difference in the advance of vegeta- 

 tion between the two valleys is three or four weeks, and found an easy 

 explanation for it by taking the temperature of their respective streams. 

 Thus, on February 21, between 9 and 10 o'clock a. m., the temperature 

 of the Rio del Norte, just above the junction, was 49°, while that of the 

 Conchas was 58°, and that of the conjoined rivers (now Rio Grande) 55°. 



