MAMMALS OF THE MEXICAN BOUNDARY. 127 



a laguna of the Colorado Eiver, at the east edge of the bottom land. 

 Willow, Cottonwood, and mesquite are the prevailing trees, and 

 arrowwood, hemp, and amaranth the characteristic undergrowth. 

 Mr. Holzner occupied this station from March 13 to "31, 1894, and 

 the writer from March 13 to 23 and 30 to 31, 1894. Collecting was 

 extended across the western half of the Yuma Desert and across the 

 bottom land to the edge-ef the Colorado Eiver. Nowhere were larger 

 collections made in the same length of time. 



Flora of lower Colorado River. — The vegetation from the mouth 

 of the Gila to the Gulf of California is disappointing to a stranger 

 expecting to view tropical scenery. Beyond the broad river bottom, 

 which is subject to regular seasonal overflowing, the Colorado is lat- 

 erally bounded by broad and barren deserts, the Yuma Desert on the 

 east and the Colorado Desert on the west. The river channel is 

 marked by a line of unusually tall cottonwoods and a lesser fringe 

 of willows {Salix fluviatilis). The adjacent bottom lands are cov- 

 ered more or less with mesquite and tornillo {Prosofis glandulosa 

 and P.odorata). The common shrubbery is a dense and monotonous 

 growth of arrowwood {Pluchea sericea) and, in places, of Baccharis. 

 There are but few cacti, and these only in the hilly granite country 

 in the vicinity of Yuma. No species of cactus, Yucca, Agave, Nolina, 

 or Dasylirion was seen on the flat country between Yuma and the 

 Gulf nor on the bordering deserts. Gourds and spiny asters cover 

 the ground not otherwise occupied for several miles below Yuma. 

 Then, about 26 kilometers (16 miles) below Yuma begins a rank 

 growth of wild hemp' that extends to the Gulf of California. This 

 plant is 2 to 6 meters high, varying according to soil and moisture, 

 and commonly grows with a coarse species of amaranth, which at- 

 tains about the same height. Elder (Sambucus glauca) grows spar- 

 ingly along the Colorado banks and is commonly cultivated in the 

 settlements. About Yuma, most mesquite trees are small and heavily 

 laden with globular masses of mistletoe, Farther south the parasite 

 is less abundant and the trees larger, though inclined to a prostrate, 

 straggling growth, many trunks arising from a single bole, the 

 branches radiating and drooping, so that the terminal twigs sweep 

 the ground or are buried in the soil. Some of these trees are very 

 large, covering an area of 50 meters or more in diameter. The bark 

 is much gnawed off by an arboreal species of the wood rat {Neotoma 

 cumulafor), whose bulky nest of sticks, coyote melons, and rubbish 

 is built up into the dependent branches. A coarse Ephedra has a 

 predilection for the slopes between the edge of the desert mesa and the 

 river bottom. Wild tobacco {Nicotiana glauca) grows along the 

 Colorado and its acequias, having probably escaped from cultiva- 

 tion. A small native species is also common. The indigo thorn. 



