BETULACEA., 
SILVA OF NORTH AMERICA. 45 
BETULA. 
FLOWERS unisexual, moneecious, apetalous, the staminate in long pendulous aments ; 
calyx membranaceous, 4-lobed ; stamens 2; the pistillate in erect cylindrical aments ; 
ovary naked, 2-celled; ovule solitary in each cell, suspended. Fruit a winged nut 
covered by the enlarged scale of the ament. Leaves alternate, dentate or serrate, 
stipulate, deciduous. 
Betula, Linnzus, Gen. 285 (1737). — Adanson, Fam. PI. ii. 
375 (in part). — A. L. de Jussieu, Gen. 409 (in part). — 
Endlicher, Gen. 272 ; Suppl. iv. pt. ii. 19. — Meisner, Gen. 
351. — Baillon, Hist. Pl. vi. 254. — Bentham & Hooker, 
Gen. iii. 404. — Prantl, Engler & Prantl Pflanzenfam. 
iii. pt. i. 43. 
Betulaster, Spach, Ann. Sci. Nat. sér. 2, xv. 198 (Revisio 
Betulacearum) (1841). 
Trees or shrubs, with watery juice, furrowed scaly resinous bark smooth on young stems, marked 
with long horizontal lenticels and often separating into thin papery plates, hard close-grained wood, 
slender tough terete branches marked with pale lenticels persistent for many years, and furnished with 
short stout spur-like two-leaved lateral branchlets conspicuously roughened by the crowded leaf-scars of 
many previous years, elongated buds full grown at midsummer and in winter covered by ovate acute 
scales, those of the mner ranks accrescent and marking in falling the base of the branch with persistent 
ring-like scars,’ and fibrous roots. Leaves open and convex in the bud, becoming conduplicate or even 
revolute as it expands, obliquely plicately folded along the primary veins,’ alternate, dentate, usually 
doubly, often incisely lobed, penniveined, the veins running obliquely to the points of the teeth, 
petiolate, persistent, deciduous, leaving when they fall small semioval leaf-scars displaying the ends of 
three equidistant fibro-vascular bundles. 
the leaf in the bud, caducous. 
leaves, moneecious, sessile, in three-flowered cymes in the axils of the scales of pendulous or erect. 
Stipules ovate, acute, or oblong-obovate, scarious, inclosing 
Flowers opening in early spring, with or before the unfolding of the 
aments, the lateral flowers of the cyme subtended by bractlets adnate to the base of the scale. Stami- 
nate aments pendulous, elongated, solitary or clustered, sessile or short-pedunculate, appearing in the 
summer or autumn in the axils of the last leaves of the branch of the year, or near the ends of the short 
lateral branchlets of the year, or rarely from the axils of all but the upper leaves of the year,’ erect and 
naked during the winter ; scales broadly ovate, rounded, short-stalked, yellow or orange-color below the 
middle and dark chestnut-brown at the apex. Calyx sessile, membranaceous, irregularly four-lobed or 
usually two-lobed by suppression, the anterior lobe obovate, rounded at the apex, concave, as long as 
1 Betula does not form a terminal bud, the end of the branch of leaves for many years, and finally grow into branches which may 
dying and falling during the summer, leaving a minute circular also develop flowering branchlets from the axils of their primary 
scar close to the upper axillary bud, which prolongs the branch the leaves. 
following season. 
2 Henry, Nov. Act. Acad. Ces. Leop. xviii. 527, t. 39. 
The sterile leaf-buds, which are usually confined, except on young 
plants, to the terminal branches, are covered with two opposite pairs 
of scales, and the buds on the short lateral branchlets, which con- 
tain two leaves and the pistillate inflorescence, are inclosed by sev- 
eral loosely imbricated scales, the lowest being sterile. The short 
lateral branchlets continue to produce pistillate aments and pairs 
8 In Betula pumila and Betula nana the staminate aments are 
usually produced singly from leafless or rarely leafy buds in the 
axils of all but the three or four upper leaves of the shoot, and 
are therefore below the pistillate catkins, which are terminal on 
the leafy shoots of the year from buds in the axils of the last 
leaves of the previous year. In the other species of Betula which 
I have been able to examine, the staminate aments are higher on 
the branch than those containing the pistillate flowers. 
