LIST OF ILLUSTRATIONS xiii 



Fig. Pace. 



113. A. Forest of giant Cacti (Cereus giganteus) near Tucson, in 



Arizona. Opuntia in the foreground. Ocotillo, tree- 

 cactus, and Palo Verde in the middle .... 349 



114. The desert botanical laboratory at Tucson, Arizona, with 



two shrubs of Ocotillo {Fouquieria spletidens), giant cacti, 

 Opuntia, tree-cactus, and other shrubs . . -351 



