282 THE CULTIVATED EVERGREENS 



scaly; branchlets glabrous, grayish- or pale-brown; winter-buds ovoid, obtuse, 

 with glabrous, usually loosely imbricated scales, rounded and bifid at the 

 apex: leaves quadrangular, acute or acutish, slightly curved, }/i-'^i inch 

 long, more or less bluish-green, of strong disagreeable odor when bruised: 

 cones cylindric-oblong, 13^-2 inches long, pale brown and lustrous, green 

 before maturity; scales suborbicular, with rounded entire margin. Labrador 

 to Alaska, south to Montana, Minnesota, and New York. — Introduced 

 about 1700 to Europe. Hardy as far north as Labrador and Saskatchewan. 

 An ornamental species of dense habit when young and with rather light 

 bluish-green foliage; it endures heat and drought much better than the two 

 preceding species. 



Var. caerulea, Rehd. (P. canadensis coerulea, Schneid. P. alba coerulea, 

 Carr. P. alba argentea and var. glauca, Hort. Abies rubra violacea. Loud.). 

 Silver White S. Of dense habit, with light bluish-green or almost silvery- 

 white leaves. Var. aurea, Rehd. (P. alba aurea, Beiss.). Golden White S. 

 With golden-yellow foliage. 



An important geographical variety is var. albertiana, Sarg. (P. canadensis 

 var. albertiana, Rehd. P. albertiana, S. Br. P. alba albertiana, Beiss.). 

 Alberta S. Tree to 100 or occasionally 150 feet, of narrow-pyramidal habit; 

 branchlets sometimes minutely pubescent; winter-buds slightly resinous, 

 with entire scales, the basal ones acuminate: leaves more crowded; leaf- 

 cushions longer: cones shorter, with more rigid, rounded, slightly denticulate 

 scales. British Columbia to Wyoming and Montana.— Introduced in 1906 

 by J. M. Macoun. The "Black Hills" spruce belongs here; it is said to be a 

 very compact pyramidal tree of slow growth. Var. conica, Rehd. (P. alberti- 

 ana, Hort., not S. Br.). A dwarf form of the preceding variety of dense, narrow- 

 conical habit, with radially spreading, thin, slender leaves M-H "ich long. 

 Introduced in 1904 to the Arnold Arboretum by J. G. Jack. 



Section II. Casicta, Mayr. 



Leaves quadrangular or compressed and with few rows of stomata on the 

 lower side or none: cone-scales loosely appressed before maturity, at maturity 

 thin and flexible, usually rhombic, with erose and more or less wavy margin. 



20. P. Engelmanni, Engelm. (P. columbiana, Lemmon. P. pseudopungens, 

 Dieck. Abies covimidata, Murr.). Engelmann S. Fig. 74 and Plate 

 XXXVII. Tree to 150 feet tall, with slender spreading branches in closely 

 arranged whorls, forming a dense and narrow pyramid in young trees; winter- 

 buds with brownish-yellow, usually appressed or little spreading scales; 

 branchlets pale brownish-yellow, pubescent: leaves more or less directed 

 forward, slender, straight or slightly incurved, acute, bluish-green to steel- 

 blue, J^-1 inch long, without resin- canals, of a strong aromatic odor when 



