12- 



determined in various localities and for different soils. For a 

 more complete description of these the reader is referred to the 

 various publications relating to this subject. Only a generaliz- 

 ed list is here possible as the complete range of depth to which 

 roots extend has not been sufficiently determined, the same 

 species having more extensive root systems under some soil and 

 moisture conditions than under others. The texture of soil, its 

 capacity for capillary moisture, its permeability to rainfall as 

 affected by soil type, slope, and surface conditions (12) in addi- 

 tion to the amount of precipitation, are important factors in 

 determining the limits of depth to which roots may extend. 



Studies of the relation of mesquite ( Prosopls ) to ground 

 water, by Brown (8) and others, have definitely placed it as a 

 ground-water plant that grows within a wide range of depth limits. 

 The normal habitat of mesquite growth is the lowlands of south- 

 western deserts, but it grows well also in other regions having 

 altitudes of from 2,000 to 3,500 feet. It is sometimes found in 

 upland draws at some distance from the lowland areas where the 

 water table is not too far below the surface. 



Mesquite thickets occupy the lowest valleys where ground 

 water is most readily available and such conditions may produce 

 trees from 10 to UO feet in height. As depth to water increases 

 the mesquite gradually diminishes in size until usually it ceases 

 to exist where depth to ground water exceeds 40 to 50 feet. Such 

 depths are unusual for ground-water plants. Of it, as a desert 

 plant, Spalding has written: (28) "It (the mesquite) is commonly 

 armed with spines, and its coriaceous leaves are well protected 

 against excessive transpiration. It is a plant requiring a better 

 water supply than many of its associates, yet well adapted to the 

 low relative humidity of the desert air, and its occurrence beyond 



its own special area, corresponds with this peculiarity. 



Thus it is, in a sense, a desert plant, yet one of high water re- 

 quirement -- characteristics which it shares with various other 

 species. " 



