DRY FARMING CONGRESS. 



245 



Tucson, but a little farther down other springs may again supply the chan- 

 nel with water, so that gardens and small ranches may be irrigated, as 

 will be found to be the case near the city of Tucson. A third small canal 

 system is taken out a few miles below Tucson, supplying a few ranches, 

 and then the water disappears altogether only to be discovered by the 

 digging of wells. However, the wide strip of mesquite trees persists, and 

 the experienced plainsman knows that wherever these mesquite trees are 

 found water may be had for the digging. In some of the newly eroded 

 channels near Tucson, I photographed the banks where masses of mes- 

 quite roots were hanging like ropes from trees still growing upon the top 

 of the bank, and ready to be dislodged by the next heavy flood which 

 should erode the soil from under them. The secret of their existence was 

 revealed. They have been able to send roots down through the mellow 

 soil and gravel, in some instances, 20 or 30^ feet, to the layer of perma- 

 nent water. The Santa Cruz River, then, is a real river, but running, as 

 the old plainsman declared to be the case regarding the headwaters of 

 the Saline River in western Kansas "bottom side up" — sand and gravel 

 above and water below. While these mesquite trees are true desert trees, 

 on the other hand, they are adaptiiig themselves to peculiar conditions, but 

 still securing a fairly abundant supply of moisture. They are not the true 

 drouth resistant trees. 



The True Desert Plants. 



Passing from the mesquite belt of the valley toward the high ground 

 on either side one soon comes into a zone of that much abused shrub, 

 variously known as greasewood, creosote bush, and botanically as Co- 

 vellia or Larrea. Whenever this is reached we know that the area where 

 trees may penetrate to a subterranean source of water has passed, and that 

 we are now in a community of plant life where they must subsist on the 

 moisture afforded by the local rainfall. Yet these creosote bushes will 

 be found growing in considerable luxuriance, and with them associated 

 other species, all apparently able to thrive -in their environments and 

 maintain a vigorous existence. The investigations of Dr. Cannon, of the 

 Desert Laboratory of the Carnegie Institute, at Tucson, Ariz., have shown 

 that the root systems of the creosote bush and also of the Giant Cactus, 

 which grows upon still higher ground, consist of frequent branching su- 

 perficial roots radiating at a depth of only a few inches below the surface 

 of the soil, and prepared to appropriate very quickly the rain that pene- 

 trates the soil. 



The traveler cannot avoid the thought that if species of economic 

 value for the production of fruit or other products could be found equally 

 well adapted to these conditions these vast stretches of mesa might be 

 made to yield fair revenues for the support of mankind. 



Have we any cutlivated plants of economic importance able to exist 

 under similar conditions, having a branch and leaf system able to resist 

 the burning heat and evaporation of the desert atmosphere and a root 

 system able to appropriate the scant moisture that falls upon the ground, 



