366 



FOEEST TREES OF THE PACIFIC SLOPE. 



when they are wounded. This hardens with exposure, and has the mucilagi- 

 nous qualities of gum arabic, as a substitute for which it is sometimes used. 



Longevity. The life limits of mesquite, below and above ground, have 



not been worked out fully, but the tree is unquestionably long-lived, though of 



Fig. 171. — Prosopis juliflora planrfulosa. 



exceedingly slow growth. Trunks from 10 to 12 inches in diameter are from 

 100 to 125 years old, while the larger trunks occasionally found are likely to be 

 very much older. 



