THE GTMNOSPERM TREES 265 



largest measured tree of this species was about three hundred 

 eighty five feet in height and fifteen feet in diameter, which 

 would give it the record height growth for a tree in North 

 America. When both height and diameter are considered, it is 

 exceeded only by the giant Sequoias of California. Due largely 

 to the presence of this giant species in both pure and mixed 

 stands forming dense growths, the Pacific Northwest forest has 

 the distinction of being the most heavily wooded region in the 

 world. The great concentration of timber which is found in this 

 region can only be appreciated when it is realized that this forest 

 region, which represents only 1 3% of the commercial forest area 

 of the United States, contains 

 63% of the total standing saw- 

 timber of the country. About 80% 

 of the standing Douglas fir is 

 found in Oregon and Washington. 

 Though inhabiting a wide variety 

 of soils, best growth is made on 

 deep, rich soils in regions where 

 both soil and air are plentifully 

 supplied with moisture. The lar- 

 gest trees are commonly five fi^. 186.— Hemlock has soli- 

 hundred years old, but trees large tary flattened needles which are 

 enough to yield saw logs may be among the smallest of all the 

 grown in less than eighty years needle-leaved evergreens. 

 since, under favorable conditions, growth is very rapid in 

 young trees. At the present time this species is the most important 

 source of construction lumber and timbers, even exceeding south- 

 ern pine in quantities produced. 



The Douglas fir of the Rocky Mountain region is a much 

 smaller tree, rarely exceeding a height of a hundred and thirty 

 feet. It seems much more able to thrive under adverse conditions 

 than does the coast form, and is commonly associated with 

 ponderosa pine in arid parts of this region. This more resistant 

 form is often used as an ornamental tree in the east. 



The Hemlocks 



Hemlocks (Tsuga) have single, spirally arranged leaves 

 which appear as though borne in two ranks (fig. 186). They are 



