56 
The Canadian River is a southern tributary of the Arkansas, run- 
ning eastwardly very nearly under the 35th degree of latitude, and 
bounding on the north the. elevated plains known as the Llano Esta- 
cado, in the northwestern parts of Texas and the adjoining regions of 
New Mexico. 
The Upper Rio Grande runs through New Mexico from north to 
south; the capital, Santa Fé, is not far from the river, in lat. 354°; 
and the town of Albuquerque is a little below. Dofiana is a small 
place on the river, above El Paso. El Paso itself, where the Rio 
Grande breaks through the mountain ranges, changing its heretofore 
southern to a southeastern course, is the central point of our Cactus 
region, partly from its geographical position, and partly because many 
of our explorers have made it the centre of their operations. 
The present southwestern boundary of the United States runs from 
El Paso irregularly westward through the former Mexican State of 
Sonora, to the Colorado ‘of the West,” or “of California,”? which 
comes from the South Pass in the Rocky Mountains, and runs south- 
westward and southwardly. Its principal tributaries rise in the east ; 
those most important to us are the Little Colorado or Colorado Chi- 
quito, under the 35th and 36th degree of latitude; Bill Williams’s 
Fork, or Williams’s River, as it is lately styled, further south; and 
in lat. 33° the Gila River, which rises near the ‘* Coppermines,”’ north- 
west of El Paso. 
Proceeding from Santa Fé westward, we find the Indian town of 
Zuni, on the head-waters of the Little Colorado; then the San Fran- 
cisco mountains; the Cactus Pass, at the head of Williams’s River, 
and this stream itself. All this territory is at present included in the 
political organization of New Mexico, though uninhabited by whites. 
of the Colorado, in lat. 35°, is the Mojave or Mohave River, 
rising in the Sierra Nevada near the Cajon Pass; lower down, oppo- 
site the mouth of the Gila, the country is a sandy desert extending 
westward nearly to San Felipe, on the eastern slope of the California 
mountains in the same latitude. On the western sea-coast the town of 
San Diego is the only interesting point for the plants under review. 
Geographical Distribution of the Cactacee in the Territory of the 
United States. 
As to the geographical distribution of the Cactacea, our territory 
may properly be divided into eight regions, viz. : — 
