SHREVE: ACROSS THE SONORAN DESERT 291 
Whereas the hills are the optimum habitat for arborescent cacti 
in the interior, at this locality they are bare of all but a few small 
individuals. 
On approaching Punto Kino the eye is arrested by what 
appears to be a forest of small trees denuded of their branches 
and leaves, extending along the base of the hills. This proves 
to be the cirio, Idria columnaris, of the family Fouguieraceae, 
previously known only on the peninsula of Lower California. 
The trunk of this singular tree is from 12 to 18 in. in thickness 
at the base but tapers very rapidly to a slender top and rarely 
Idria columnaris, on tocky etic near Punto Kino, Sonora. 
Fic. 3. 
The trees in the center are Elaphrium Macdougali 
exceeds 20 ft.in height. The trunk itself occasionally forks into 
two or three branches, all of which continue to grow in a vertical 
position. From base to top the trunk is beset with short slender 
lateral branches, growing in a horizontal position and bearing 
thorns and seasonal leaves after the manner of Fouquiera. The 
large racemose inflorescences are borne only at the upper end 
of the trunk or its branches. The trunk is smooth, of a pale 
salmon color, and the cortex is so soft that it can be cut with 
greatease. There is ligneous tissue throughout the cross section 
of the trunk, but the trunk also serves as a reservoir for a con- 
siderable quantity of water. The very young individuals of 
