10 



big greasewood ( Sarcobatus vermiculatus ) growing under similar 

 conditions . 



The extensive primitive grassland communities of the Great 

 Plains did not support a uniform vegetation. The rainfall of the 

 eastern portion moistens the ground to a depth of several feet, 

 promoting a distinctive cover of prairie grasses 1 to 5 feet in 

 height. Characteristic of the region, as listed by Weaver (37), 

 are the bluestem grasses ( Andropogon ) which supply the bulk of 

 the wild prairie hay, the tall panic grass (Panicum virgatum ) , 

 tall marsh grass ( Spartina michauziana ) which also furnishes an 

 abundant foliage, and other plants. 



There is likewise a distinction between ground-water plants 

 that feed upon fresh water and those that are tolerant of water 

 slightly alkaline. Plants of this type are more or less salt- 

 resistant. Saltgrass ( Distichlis spicata ) is an important unit 

 in this group. It is found often in areas of shallow water table, 

 the limit of depth from which the roots may draw moisture depend- 

 ing upon soil type. Being a salt-resistant plant it is not an 

 excessive user of water, and unless the water table is within 24 

 to 30 inches of the ground surface the water transpired will prob- 

 ably be less than that required by most cultivated crops. 



In many localities succulents are identified with alkaline 

 conditions resulting from areas of high ground water. 



Riparian vegetation, as alders, sycamores, and cottonwoods, 

 growing in canyon bottoms where the roots are fed by percolation 

 from the stream bed, uses large amounts of water. Seepage from 

 irrigation canals often feeds the roots of willows, cottonwoods, 

 sweetclover (Melilotus sp . ) , and other ditchbank vegetation. 

 Such growth is sometimes troublesome in canal management. 



INDICATOR VALUE 0? GROUND-WATER PLANTS 



The value of many species of arid land vegetation as indi- 

 cators of ground water has long been recognized in the geological 

 and botanical investigations of southwestern desert areas, yet 



