A SOUTHWESTERN PLANT GROUP. 787 



extensive and vitally important place in the economy of Nature. 

 Of these last few one instance rises up most prominently of all, 

 certainly without a full parallel elsewhere in the field of botanical 

 science and do we realize that it stands almost at our doors ? It 

 is the great three-typed plant group that forms the major part of 



FIG. 2. CEREUS TRIANGTJLARIS. 



the flora of the far Southwest, on the arid plateaus and plains and 

 rocky mountain heights of Arizona and New Mexico, western 

 Texas and southernmost California, and over the boundary line 

 far into northern Mexico. Here is the fatherland and here the 

 supreme province of those three marvels of plant life the cacti, 

 with their strangely specialized vegetative body ; the agaves, to 

 which popular tradition has attached an epithet of fitting dignity 

 in the name of " century plants " ; and, thirdly, the yuccas, which 

 claim, in addition to their floral splendor, the distinction of mani- 

 festing the interdependence of the flower and insect worlds with 



