97 
Perhaps the most difficult part of my task on this expedition 
was the collection and shipment of specimens of the tree cactus or 
“Saguaro” (Cereus giganteus). This interesting plant consists 
of a main trunk of a diameter of one to two feet which reaches a 
height of thirty-five to sixty feet. Ordinarily a few branches arise 
from the trunk at a distance of five to ten feet from the base, which 
are at first horizontal, but which finally curve upward like the 
branches of a candelabrum. The formation of the branches does 
not take place until the main trunk has reached a height of twelve 
Fic. 16. Cereus giganteus about twenty-five years old, 13!4 feet high, near 
‘Tucson, Arizona. This specimen is now in conservatory house No. 6. 
to twenty feet. The trunk has an internal woody cylinder about 
six to ten inches in diameter enclosing a pith saturated with a 
bitter juice, and the outer portion of the trunk embracing the 
