Plant AssociATtoisrs at the Desert Laboratorv. 



59 



According to Bray, "its spread northward and eastward from the 

 Rio Grande country during the past 50 years has been a marked 

 phenomenon. By its invasion, mile after mile of treeless plain 

 and prairie have been won and reduced to a characteristic orch- 

 like landscape. It has traveled northward over the Staked 

 Plains, covering half their area, and has passed over Oklahoma 

 and into southwest Kansas. This encroachment of mesquite 





Fig. 



\'egetation of Tumamoc Hill; sahuaros, opuntia and palo verdo conspicuous. 



is partially accounted for by its weed-like capacity for occupy- 

 ing new ground . . . and by the influence of cattle in scat- 

 tering the beans." Such extensive and rapid invasion as are 

 here described has not been observed in Arizona, so far as the 

 writer is aware, but the same characteristics are noted here — • 

 its preference for low, fiat areas, with compact soils, but with a 

 marked capacity for extending beyond these on to higher ground, 

 its successful reproduction where it is really at home, and the 

 tenacity with which it holds its place where once established. 

 Its endurance of conditions to which various other species are 

 less fitted is w^ell seen in many places from Texas to California, 

 and particularly in the Salton Basin, where great mounds of 

 sand are blown about the mesquite, which keeps on growing, its 

 branches extending beyond the rising heap or dune, until the 



