1909] _ PHILLIPS—A STUDY OF PINON PINE 219 
shade of older trees. After the seedling stage is passed it prefers the 
open, and is one of the most intolerant of forest trees. This gives an 
orchard-like appearance to most stands of this species. Occasionally 
stands of 0.7 density were noted, although few stands have more 
than 0.6 density. 
On the best sites the trees reach a maximum height of 12 to 13.7™ 
(40 to 45 feet) and a diameter of 60 to 75°™ (2 to 2.5 feet) at breast 
height, but ordinarily the mature individuals range from 3 to 10.5™ 
(10 to 35 feet) in height and from 15 to 45°™ (0.5 to 1.5 feet) in diam- 
eter. A difference in development was apparent on different sites. On 
exposed sites the tree is globular, very scraggly when mature, and 
has little or no clear length. On favorable sites trees in the open 
have a very short clear length and a fairly regular globular or egg- 
shaped crown. If grown in stands, the trees have a greater clear 
length and a flat or vase-shaped crown. Young trees on favorable 
sites are conical or globular in shape and usually very regular in 
form. 
On the most exposed sites, shrublike trees were found which 
were fifty to eighty years old, and only 1.8 to 3™ (6 to 10 feet) in 
height, with a crown diameter reaching a maximum of two to four 
times the height of the tree. On such trees it was impossible to dis- 
tinguish the leader from the branches, and the general appearance 
of the tree was much like that of the dwarf mountain pine (Pinus 
monticola). The foliage is more densely clustered on these dwarf 
trees than it is on trees in the open, with shorter and apparently 
thicker leaves. Practically all trees, whether growing on poor or 
800d sites, are characterized by dead and half-dead branches, which 
are retained on the tree for several years. This is characteristic of 
nearly all species in the southwest and is due to the small amount of 
Stowth that is made, the necessity of retaining only a small amount 
of living tissue, and the dry nature of the climate, which allows the 
retention of dead branches for a longer period than would a moist 
Climate. In exceptional stands, such as occur to the west of Servil- 
leta, New Mexico, where a clear length of 4.5 to7.6™ (15 to 25 feet) 
'S not exceptional, the branches are shed largely because the density 
of stand prevents the formation of as large branches as are found in 
those trees which enjoy full sunlight. 
