SPRUCE AND BALSAM FIR TREES. 29 



the bracts borne on the backs of the cone scales of both trees also 

 differ materially in form. No constant distinguishing characters 

 can be found in the seeds (PI. XI, 6, c and PL XIV, b, c). The seed- 

 leaves of cork fir are commonly four in number, and about one-half 

 an inch long. 



The wood of Abies arizonica is similar in external appearance to 

 that of alpine fir and useful for the same purposes. It is commer- 

 cially unimportant, except where the timber can be cut with alpine 

 fir, from which when sawed into lumber it can not be distinguished 

 in its general appearance. 



OCCURRENCE AND HABITS. 



Cork fir grows on disintegrated rock and in gravelly soils or on 

 thinly covered rock at elevations between about 8,000 and 10,000 

 feet, and usually on northern slopes and benches, but sometimes on 

 exposed ridges and high peaks (Map No. 7). In some instances it 

 forms nearly pure groups or stands of limited extent interspersed 

 with Engelmann spruce and alpine fir, or is scattered in dense stands 

 of the latter tree. Not infrequently very widely separated trees are 

 found in a mixed stand of Engelmann spruce and alpine fir. 



Cork fir is equally as tolerant of shade as the alpine fir, young 

 trees maintaining themselves for many years under dense shade in a 

 completely suppressed condition. But with the admission of top 

 light such growths readily recover and grow rapidly. 



Little is known at present of the seeding habits and reproductive 

 capacity of this fir. An abundance of cones are produced periodi- 

 cally — usually about every 3 years, while some trees bear a few cones 

 nearly every year. Only a small percentage of the seeds are fertile. 

 The ripe cones are " cut down " by squirrels, along with those of the 

 associated alpine fir, and a good many seeds are eaten by these 

 rodents. Small dense patches of suppressed seedlings are frequent 

 near fruiting trees, particularly in the washed soil of depressions and 

 in the soil-filled crevices of exposed rock on northern slopes. 



LONGEVITY. 



The age limit of cork fir is imperfectly known at present. Like 

 alpine fir it is probably only a moderately long-lived tree, not exceed- 

 ing 150 to 175 years. Trees from 6 to 12 inches in diameter are from 

 45 to 90 years old. 



GRAND FIR— "WHITE FIR." 



Abies grandis Linclley. 



COMMON NAME AND EARLY HISTORY. 



Lumbermen and other woodsmen know this tree commonly as 

 "white fir," because of the whitish, smooth bark of its upper stem. 



