BOTANICAL LABORATORY IN THE DESERT. 339 



View on the Laboratory Hill, Giant Cacti. 



ary leaves develop. The bark of the ocotillo is waxy and burns like 

 a candle. 



But whatever of unusual beauty or peculiarity the palo verde or 

 ocotillo possess, the plant which of all claims and holds the attention 

 the most constantly is the great sentinel-like saguaro or giant cactus 

 (Cereus gigantens) . Until middle age it is a single green fluted 

 column, with a nature-wrought entasis, a form of severe simplicity 

 scarcely less emphasized when, in its later growth, a few arms grow out. 

 These are usually found at some distance below the middle point of the 

 main shaft, and, though for the most part erect, sometimes, partly by 

 accident, take most grotesque positions. The woody skeleton is not 

 extensive, consisting of slender ribs which occasionally anastomose. 

 These are used by the Papagos for palings and to form the frame of 

 their burden frame or quijo. 



The saguaro flowers in June, producing at the top of the stem 

 a large cluster of tubular white petaled flowers in which are found hun- 

 dreds of small beetles and wasps, apparently the chief agents of pollina- 

 tion. While the fruit is developing, the shriveled flowers, which re- 



Saguaro Flower and Fruit cut Longitudinally. 



