Volume 9 Number 3 



The Plant World 



SI iflaffa^inr of popular -Botanp 

 MARCH, 1906 



TWO MILES UP AND DOWN IN AN ARIZONA DESERT. 



By W'u. a. Cannon, 



Desert Botanical Laboratory. Tucson. Arizona. 



A trip across the Territor}- of Arizona from the south to the 

 north, or from the west to the east, or an ascent of any of the 

 numerous hi^h mountains, reveals several sreat floral belts, or 

 aggregations of plants, which go to make up the extremely inter- 

 esting vegetation of this portion of the arid southwest. These 

 belts, for the purposes of this paper, may be roughly classed into 

 (i) the desert belt, having the grease-wood or creosote bush 

 {CoviUca tn'dciifata) , Frauscria dnuiosa. the mesquite (Prosopis 

 vclutina) . and numerous other forms as re])resentative of the 

 vegetal covering; (2) the desert belt, at an altitude somewhat 

 higher than the last, with various yuccas, agaves and the bear 

 grass or sotol (Dasylirioii) ; (3) the higher land or mountain 

 zone with juniper and dififerent oaks; (4) the mountain zone with 

 various pines and cedars, maples, and the beech and quaking 

 aspen; and (5) the highest mountain zone which represents the 

 alpine formations. 



This vast range of plant life, continental in its scope, is made 

 possible by the varied topography of the country, which is the 

 last chapter of an interesting geological history. The northern 

 and the eastern portions of the Territor}- are plateaux and moun- 

 tains, with altitudes varying from 5,000 to over 12,000 feet above 

 the sea. The southwestern part ranges in altitude from a little 

 above sea level to about 2,500 feet except where isolated mountain 

 ranges carry the elevation 7,000 or 8,000 feet higher. 



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