36 CONTRIBUTIONS FROM THE NATIONAL HERBARIUM. 



Making due allowance for the overlapping of the various zones, 

 the following approximations of their altitudinal limits in Washing- 

 ton may be made: 



Upper Sonoraii. Go to GOO meters (200 to l.OOO feet). 



Humid Transition, to 1.200 meters (0 to 3.800 feet). 



Arid Transiti(jn, 500 to 1,300 meters (1,G00 to 4,200 feet). 



Ciuuidlan, 400 to 1.500 meters (1,400 to 5.000 feet). 



Iludsoniau, 1,500 to 2,100 meters (5.000 to 7.000 feet). 



Arctic, 1,800 to 3,200 meters (G,000 to 10,500 feet). 



UPPER SONORAN LIFE AREA. 



This comprises the western or arid portion of the Upper Austral 

 life zone. It occupies much of the Columbia and Great basins, and 

 the lower portions of the Great Plains eastward to about the one 

 hundredth meridian. It also extends southward into Mexico at 

 increasing elevations along both sides of the Rocky Mountain system. 

 In Washington the area is confined to that portion east of the Cascade 

 Mountains below a contour line approximating 360 meters (1,200 

 feet), but on southerly slopes it may extend up to 510 meters (1,700 

 feet), or even more. 



From an agricultural standpoint this zone is that in which the 

 commercial culture of such crops as tomatoes, peaches, apricots, and 

 Avatermelons is possible. 



In Washington the most conspicuous plant of this zone is the 

 sagebrush {Artemisia tr id entata) (PL VI). It marks quite sharply 

 the limits of the Upper Sonoran zone, seldom extending into the zone 

 above, as it commonly does farther southward. Other characteristic, 

 if less abundant, shrubs are rabbit brush {Ghrysothamnus nauseosu-s 

 and C. viscidiflorus) , hop sage {Grayia spinosa), antelope brush 

 {Kunzia tridentata, locally known as black sage), and, in alkaline 

 situations, greasewood {Sarcohatus verTuicidafus) . In a few locali- 

 ties the sagebrush is absent, but in such cases one or more of the other 

 characteristic shrubs is sure to be present. 



Excepting such species as are confined to the moist gi'ound along 

 perennial streams, the great majority of the Upper Sonoran plants 

 are either shrubs or thick-rooted perennial herbs or short-lived 

 annuals. 



There are in Washington about 500 species of plants which occur 

 in this life zone. Of this number 243 species occur in no other life 

 zone— that is, are distinctive. Furthermore, of this last element 31) 

 species are confined in their distribution to the Columbian Basin of 

 Washington, Oregon, and Idaho, several of them being quite rare 

 and local. 



