BETULACES, SILVA OF NORTH AMERICA. (6 
ALNUS TENUIFOLIA. 
Alder. 
Leaves ovate-oblong, glabrous or puberulous on the lower surface. 
Alnus tenuifolia, Nuttall, Sylva, i. 32, t. 10 (1842). XXXViili. pt. ii. 433 (Gattungen Betula und Alnus) (1865) ; 
? Alnus incana, £, Hooker, Fl. Bor.-Am. ii. 157 (1839). De Candolle Prodr. xvi. pt. ii. 188 (in part). 
Alnus incana, a glauca, Regel, Nowy. Mém. Soc. Nat. Alnus viridis? Cooper, Am. Nat. iii. 408 (1869). 
Mosc. xii. 154 (Monographia Betulacearum) (in part) Alnus incana, var. virescens, Watson, Brewer & Watson 
(1861) ; Bull. Soc. Nat. Mosc. xxxviii. pt. ii. 433 (Gat- Bot. Cal. ii. 81 (1880).— Sargent, Forest Trees N. Am. 
tungen Betula und Alnus) (in part) ; De Candolle Prodr. 10th Census U. S. ix. 165. 
xvi. pt. ii. 189 (in part). — Watson, King’s Rep. v. 323 (not Alnus rhombifolia, Macoun, Cat. Can. Pl. 438 (not Nut- 
Aiton) ; Pl. Wheeler, 17. — Macoun, Rep. Geolog. Surv. tall) (1883). 
Can. 1875-76, 210. — Rothrock, Wheeler’s Rep. vi. 239. ?Alnus occidentalis, Dippel, Handd. Laubholzk. ii. 158, 
? Alnus serrulata, B rugosa, Regel, Bull. Soc. Nat. Mose. f. 78 (1892). — Koehne, Deutsche Dendr. 114. 
A tree, occasionally thirty feet tall, with a trunk six or eight inches in diameter, and slender 
spreading slightly pendulous branches which form a narrow round-topped head; or more often shrubby 
in habit, with several spreading stems, and at the north and at high elevations frequently not exceeding 
four or five feet in height. The bark of the trunk is not more than a quarter of an inch thick, light 
red-brown, generally smooth but broken on the surface into small closely appressed scales. The 
branchlets are slender, and when they first appear are marked with a few large orange-colored lenticels 
and coated with fine pale or rusty caducous pubescence ; during their first winter they are ight brown 
or ashy gray and more or less deeply flushed with red, and in their second season gradually grow paler 
and lose their lenticels. The winter-buds are from a quarter to a third of an inch in length, with bright 
red puberulous scales. The leaves are ovate-oblong, acute or acuminate, broad and rounded or cordate, 
or occasionally abruptly narrowed and wedge-shaped at the base, usually laciniately lobed, with acute 
lobes, and doubly serrate with nearly triangular spreading gland-tipped teeth ; when they unfold they 
are light green often tinged with red, pilose on the upper surface and coated on the lower with pale 
tomentum, and at maturity they are thin and firm, dark green and glabrous above, pale yellow-green 
and glabrous or puberulous below, from two to four inches long and from one and a half to two and a 
half inches wide, with stout orange-colored midribs impressed on the upper side, slender primary veins 
running to the points of the lobes, rather conspicuous cross veinlets, and stout slightly grooved orange- 
colored petioles from half an inch to an inch in length. The stipules are ovate, acute, thin and scarious, 
half an inch long, about an eighth of an inch wide, and coated with pale pubescence. The aments of 
staminate flowers, three or four in number, are borne in slender-stemmed racemes about three inches 
in length, and are nearly sessile, or are raised on stout peduncles often half an inch long; during the 
winter they are naked, light purple, from three quarters of an inch to almost an inch in length and 
about a quarter of an inch thick, and when they are grown to full size and the flowers open‘with the 
unfolding of the leaves they are from an inch and a half to two inches long. The pistillate aments, 
which during the winter are naked, dark red-brown, and nearly a quarter of an inch long, with acute 
apiculate loosely imbricated scales, enlarge slightly in early spring before the appearance of the styles; 
and when fully grown the strobiles are ovate-oblong and from one third to one half of an inch in 
length, with scales that are much thickened and truncate or three-lobed at the apex, and nearly circular 
or slightly obovate nuts surrounded by thin membranaceous margins. 
Alnus tenuifolia inhabits the banks of streams and mountain cafions, and is distributed from the 
