26 BULLETIN 460, U. S. DEPARTMENT OF AGRICULTURE. 
LONGEVITY. 
Little is known of the extreme age attained by this species. It is 
believed, however, to be moderately long-lived. Trees from 16 to 20 
inches in diameter are from 200 to 250 years old. 
YELLOW PINES. 
Trees with rather hard, heavy wood in which the early- and late-formed portions 
of the annual layers are sharply defined. 
ARIZONA PIN#. 
Pinus arizonica Engelmann. 
COMMON NAME AND EARLY HISTORY. 
Arizona pine is little, if at all, known to laymen, who usually mis- 
take it for the western yellow pine (Pinus ponderosa). This 1s prob- 
ably because of its close general resemblance to the latter tree, with 
which it is more or less associated but from which it is roughly dis- 
tinguished by the greater number of leaves it bears in each cluster or 
fascicle. 
The specific technical name of this pine, arizonica, suggested be- 
cause the tree was discovered in Arizona, is unfortunate, for the 
greater part of the range lies in Mexico. Similarly, the common 
name “Arizona pine,” derived from the technical name, is inappro- 
priate, but itis the only distinctive one available. 
Dr. John T. Rothrock, prominent in recent years in Pennsylvania 
forest work, discovered this tree in 1874 on the Santa Rita Mountains, 
southeastern Arizona. Dr. Rothrock was then serving as botanist 
and surgeon to an expedition under Lieut. Wheeler, who was making 
a geographic survey of our Southwest. The tree was technically 
described and given its present name, Pinus arizonica, in 1878. 
Since then no other technical names have been applied to it, and its 
claim as a distinct species was not questioned until 1909, when Dr. 
G. W. Shaw,? believing it to be a variety of Pinus ponderosa, gave it 
the technical name of P. ponderosa var. arizonica. The fairly con- 
stant occurrence, however, of 5 leaves in a bundle and appreciably 
distinct characteristics of the cones appear to be good reasons for still 
maintaining Arizona pine as a species. 
DISTINGUISHING CHARACTERISTICS. 
Arizona pine attains a height of from 75 to 90 feet, or occasionally 
100 feet, with a diameter of from 30 to 50 inches. The trunks are 
Pines of Mexico, 24, 1909. 
