DESERTS AND DESERT FLORA OF THE WEST 

 phylla). Above the pinon are forests of yellow 

 pine (Pinus ponderosa scopulorum). This tree is 

 characteristic of the Transition zone. Associated 

 with it is the white fir (Abies concolor). In the 

 Boreal zone between the yellow pine and tim- 

 ber-line, are forests of the bristle-cone pine (Pinus 

 aristata) and the limber pine (Pinus flexilis). 

 Above timber-line are typical Arctic-Alpine species. 



On the desert slopes of the San Bernardino 

 Mountains in southern California similar conditions 

 exist. The pifion forms an interrupted belt below 

 the typical Sierran forests, ranging in altitude from 

 3500 to 6000 feet. The juniper, here another 

 species (Juniperus calif ornicus), is abundant and 

 ranges from 2700 to 3800 feet. Excellent groves of 

 this arborescent shrub may be seen along the Santa 

 Fe route at the desert base of El Cajon Pass. 



DESERTS OF SOUTHWESTERN ARIZONA. Botanic- 

 ally the deserts of southwestern Arizona are the 

 most interesting of all the arid West. They belong 

 phytogeographically to the Sonoran region, which 

 embraces the Mexican states, Sonora, Sinaloa and 

 Baja (Lower) California. The Mexican floral ele- 

 ment is more in evidence here than it is in the Great 

 Basin or the Mohaye Desert; its yuccas, dasylirions, 

 nolinas, parkinsonias and fouquierias are common 

 and conspicuous components of the flora. The 

 giant cactus, or saguaro (Cereus gigantens), is 

 unique, the most striking feature of the landscape. 

 Its columnar trunks, ribbed and spined, stand 

 thirty to forty or even fifty feet high, giving off a 

 few erect lateral branches of almost equal diameter. 



The Desert Laboratory. When the Carnegie In- 

 stitution of Washington was organized, Mr. Fred- 

 erick V. Coville presented plans for a desert labora- 

 tory, where the complex biological problems of the 

 deserts might be studied under natural conditions. 

 His own excellent work in connection with the 

 Death Valley Expedition had pointed out the pos- 

 sibilities of intensive investigations, and the govern- 

 ing board promptly approved his plans. The result 

 was the establishment, some twelve years ago, of 

 the Desert Laboratory at Tucson. Alreadv this 

 unique laboratory, under the able directorship of 

 Dr. D. T. MacDougal, has brought forth valuable 

 contributions to the knowledge of the deserts, their 

 soils, climates and vegetation. It has become a 

 mecca for scientific investigators, and one of the 

 principal centers of botanical research in America. 



THE COLORADO DESERT OF SOUTHERN CALIFORNIA. 

 The Colorado Desert is a low depression lying 

 south of the Chuckawalla Mountains between the 



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