Lloyd, The Desert ßotan. Laboratory of thc Carnegie Instit. of Washington. 795 



Chamber, cut into thc rock below the level of the floor, and spe- 

 cial laboratories. A deck for the mounting of meteorological in- 

 strumenta sunnounts the roof. The interior finishing is in Cali- 

 fornia Redwood. Fire places and Lavatory render the winde a 

 eommoöüous and well equipped building large enough for some 

 years to come. 



The surrounding country presents features of rare beauty. To 

 the northeast Stands the ränge of the Santa Catalina Mountains, 

 its rugged topography standing out in hold relief when the sun 

 lies low in the heavens. Between, lies a low, level or gently un- 

 dulating mesa for a distance of fifteen miles, covered chiefly with 

 a uniform growth of Covillea (Larrea) Mexicana. In the water 

 courses are a few cottonwoods {Populus sp.) giving way to mesquite 

 (Prosopis velutinä) on the adjacent flats and better watered rising 

 ground. Here too is found a species of Palo verde (Parkinsania 

 Torreyana) another species (P. microphylla) of which is found 

 affecting the rocky foot-hills. Interspersed with the greasewood or 

 creosote-bush (Covillea) of the mesa are several species of Opuntia, 

 among which a "Cholla" is the most conspieuous. This plant, and 

 other closely recated species were formerly used by the Apache 

 Indians as a means of torture, and it appears that they did not 

 underestimate the effectiveness of these plants for this purpose. 

 The penetration of the spines causes exquisite pain, and few bota- 

 nists escape the experience at some time or other. The mountains 

 themselves, on aecount of their elevation, offer a wider vertical 

 ränge of Vegetation, the higher ridges being the home of the pines 

 and cedars. The main ridge, of which Mount Lemmon is the 

 highest peak, is heavily forested with yellow pine (Pinus ponderosa) 

 and Douglas Spruce (Pseudotsuga). Thus we may pass in a few 

 hours journey on horseback from the Vegetation of the desert mesa 

 to the dense forest, w r here snow, on the northerly .slopes at least, 

 Stands the wdiole year round. 



To the east may be seen the Rincon Mountains, the most pro- 

 minent feature being the bold rounded height of the Tanque verde. 

 Further to the southward stand the Santa Rita Mountains, while 

 at still greater distances rise to other langes, all with great Stretches 

 of mesa lying between. 



In the more immediate vicinity of Tucson the Vegetation may 

 be divided for the purposes of this description into two forniations, 

 that of the mesa, and that of the rocky foothills. I have already 

 mentioned the leading plants of the former, The foothills bear a 

 more varied flora, and perhaps the most characteristic of the region. 

 It is here that we find the great cactus. Cereus giganteus, or saguaro. 

 The columnar stems of this great plants stand in numbers overtop- 

 ping the rest of the Vegetation. The commonest shrub, or rather 



