LIST OF ILLUSTRATIONS xiii 



FIG. PAGE. 



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 splendens), giant cacti, 

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



