SPRUCE AND BALSAM FIB TREES. 15 



Dl.STIiNCiUlSHINti CHAKACTK1UST1CS. 



The popularity of this spruce for ornamental planting is due to 

 the exceptionally bright silvery-blue foliage 3 of some young trees. 

 The brilliant color of young trees is, however, gradually lost as they 

 grow older, the foliage of trees even 25 to 35 years old sometimes 

 being decidedly greenish and lacking in beauty. With age also the 

 early distinctly pyramidal crown, with branches down to the ground, 

 becomes thin and irregular in outline, due to the uneven growth of 

 the branches, and later the lower limbs disappear, leaving from one- 

 fourth to one-half of the trunk clear. The thick, strong branches 

 grow in rather distant circles or whorls about the trunk, and with 

 their many much-branched, stiff, upturned side branches form pecu- 

 liarly wide, flat sprays, especially in the lower and middle parts of 

 the crown. The trunk is strongly conical. Full-grown trees, which 

 sometimes form, as do some other spruces, two or more separate 

 trunks, are from TO to 90 feet, or, in specially favorable situations, 

 from 110 to about 130 feet in height. The diameter varies from about 

 16 to 48 inches, but is commonly from 16 to 24 inches. 



The bark of mature trunks is from one-half inch to 1^ inches 

 thick, rather deeply furrowed, and composed of small, thin, elon- 

 gated scales which are externally weathered to a light ash-color, 

 sometimes with a brownish tint, and a bright red-brown beneath. 

 The similarly colored bark of young trees is much thinner, irregu- 

 larly broken and roughened by thin scales. The smooth 1-year-old 

 twigs are clear reddish yellow, later becoming grayish, while the 

 large buds, about one-half inch long, are light chocolate brown. 



The quadrangular dull gray-green, blue-green, or silvery-white 

 leaves (Pis. V, b, and VI, b) are stiff and very keenly pointed. As 

 a rule, the latter characters at once distinguish this tree from the 

 frequently associated Engelmann spruce, the leaves of which are 

 bluish, but rarely as stiff and as keenly pointed as those of the blue 

 spruce. The leaves bristle from all sides of the twigs, and are from 

 seven-eighths inch to 1^ inches long on lower branches, particularly 

 of young trees (PL V, &), and one-half to three- fourths of an inch 

 long on upper cone-bearing branches (Pis. V and VI). A cross 

 section of the leaf shows one resin duct in an angle of the leaf. The 

 leaves of each year's growth remain on the branches for from 8 to 

 9 years. 



The cones, which are produced mainly on the upper fourth or 

 third of the crown, mature in one season, and are from 2|- to ty 



1 Seedlings show great variation in the intensity of the blue color of their foliage, and 

 ornamental tree growers have developed, mainly by selection, at least half a dozen named 

 horticultural " varieties " of this tree, each of which is distinguished chiefly by differences 

 in the color of the foliage, which varies from green to bluish and silvery white. These 

 forms are, however, not fixed in nature and have no stable botanical standing. One of 

 the most brightly colored of these garden forms is the so-called " Koster blue spruce " 

 {" Picea pungens var. glauca Kosteri") propagated extensively in Europe. 



10529°— Bull. 327—16 2 



