46 SILVA OF NORTH AMERICA. BETULACE. 
the stamens, much longer than the minute posterior lobe. Stamens two, anterior and posterior, inserted 
on the base of the calyx; filaments abbreviated, divided near the apex into two branches, each division 
bearing an erect subsessile half-anther, its cell opening longitudinally. Pistillate aments oblong or 
cylindrical, pedunculate or subsessile, solitary, terminal on the short two-leaved lateral spur-like branch- 
lets of the year, or rarely racemose, their peduncles bibracteolate ; scales closely imbricated, oblong-ovate, 
three-lobed, rounded or acute at the apex, light yellow-green often tinged with red above the middle, 
accrescent, becoming brown and woody at maturity and forming a sessile or pedunculate, erect or 
pendulous, short or elongated, ovoid or cylindrical strobile, usually deciduous with the nuts from the 
slender rachis. Ovary sessile, naked, compressed, two-celled, crowned with two slender spreading 
filiform anterior and posterior styles stigmatic at the apex; ovule solitary, suspended from the interior 
angle of the cell, anatropous, the micropyle superior. Nut minute, light chestnut-brown, compressed, 
oval or obovate, crowned by the persistent stigmas, marked at the base with a small pale umbilicus ; 
pericarp of two coats, the outer thin and membranaceous, produced into a narrow or broad marginal 
wing interrupted at the apex, the inner crustaceous or slightly indurate. 
Seed solitary by abortion, 
filling the cavity of the nut, exalbuminous; testa membranaceous, light brown; cotyledons fleshy, flat, 
much longer than the short superior radicle turned toward the minute apical hilum.’ 
Betula is widely distributed through North America, Europe, and central and northern Asia, its 
species sometimes forming vast boreal forests or in stunted forms covering high mountain slopes and 
inhabiting polar regions to the limits of perpetual snow. 
Nine occur in North America; of these six are trees, and three, Betula pumila? Betula 
guished.” 
1 By Regel (De Candolle Prodr. xvi. pt. ii. 162) the species of 
Betula are grouped in the following sections : — 
Evuseruta. Strobiles solitary, their bracts longer than the fruit. 
BETULASTER. Strobiles racemose, their bracts shorter than the 
fruit. 
To the second section belong only the type of Spach’s genus 
Betulaster, the Himalayan Betula alnoides, D. Don (Prodr. Fl. Ne- 
pal. 58 [1825]. — Hooker f. Fi. Brit. Ind. v.599. Betula acuminata, 
Wallich, Pl. As. Rar. ii. 7, t. 109 [1831].— Brandis, Forest Fi. 
Brit. Ind. 458, t. 56. Betula cylindrostachys, Wallich [1. c.]), and 
the Japanese Betula Maximowicziana, Regel. 
? Spach, Ann. Scr. Nat. sér. 2, xv. 184 (Revisio Betulacearum).— 
Regel, Nouv. Mém. Soc. Nat. Mosc. xiii. 67 (Monographia Betulace- 
arum) ; Bull. Soc. Nat. Mosc. xxxviii. pt. ii. 395 (Gattungen Betula 
und Alnus) ; De Candolle Prodr. l. c. 161. 
It is probable that the species of Betula intercross, like those of 
Quercus and Salix, and that natural hybrids between them are 
common, althongh comparatively few have yet been described. 
The best known is believed by European botanists to be a hybrid 
between Betula alba and Betula nana. This is — 
Betula intermedia, Koch, Syn. Fl. Germ. et Helv. ed. 2, ii. 761 
(1844). — Reichenbach, Icon. Fl. German. xii. 2, t. 624. — Regel, 
Bull. Soc. Nat. Mosc. 1. c. 406; De Candolle Prodr. 1. c. 170. ~— 
K. Koch, Dendr. ii. pt. i. 657. — Dippel, Handb. Laubholzk. ii. 170, 
f. 82. 
Betula hybrida, Regel, Nouv. Mém. Soc. Nat. Mosc. l. c. 94, t. 8, 
f. 1-12 (1860). 
Betula nana x pubescens, Koehne, Deutsche Dendr. 112 (1893). 
Betula intermedia is an erect much-branched shrub with rhombic- 
ovate or ovate-subrotund acute glabrous leaves and cylindrical 
strobiles. It has been found on the Swiss Jura, in Sweden, in the 
neighborhood of St. Petersburg, and on the Altai Mountains in 
Siberia. It often seems intermediate between the two supposed 
parents, some individuals most strongly resembling the one and 
About twenty-four species may be distin- 
some the other, but their hybrid character usually disappears in 
succeeding generations. 
In the Arnold Arboretum several plants appeared in 1888 among 
seedlings of Betula pumila which are supposed to be hybrids be- 
tween that species and Betula lenta (Betula pumila x lenta, J. G. 
Jack, Garden and Forest, viii. 243, f. 36 [1895]), as they are inter- 
mediate between these species in the size and color of the leaves, 
in the position and size of the staminate aments, and in the size 
and shape of the strobiles of fruit and their bracts. Some of these 
hybrid plants possess the aromatic flavor and perfume of Betula 
lenta, while others have no trace of it. Some produce terminal 
staminate aments like Betula lenta, and on others the staminate 
aments are axillary and lower than the fertile aments, as upon 
Betula pumila. In their small size and shrubby habit, in the color 
of their branches, and in their usually obovate bluntly toothed 
leaves pale on the lower surface, the hybrids approach Betula 
pumila, while they differ from it in their greater vigor and larger 
size and in their larger fruit and leaves. In different places in 
northern and eastern New England individual trees which are 
almost exactly intermediate between Betula papyrifera and Betula 
populifolia are known and are perhaps natural hybrids between 
these species (Sargent, Garden and Forest, viii. 355, f. 50). 
8 Linneus, Mant. 124 (1767).— Du Roi, Harbk. Baumz. i. 95, 
t. 3.— Jacquin, Hort. Vind. ii. 56, t. 122. — Wangenheim, Nordam. 
Holz. 86, t. 29, £. 61. — Willdenow, Spec. iv. pt. i. 467. — Tucker- 
man, Am. Jour. Sci. xlv. 29. — Macoun, Cat. Can. Pl. 437. — Wat- 
son & Coulter, Gray’s Man. ed. 6, 472. 
Betula Grayi, Regel, Bull. Soc. Nat. Mosc. 1. c. 406, t. 6, £. 9-13 
(1865) ; De Candolle Prodr, 1. c. 171. 
Betula pumila is a glandless shrub with slender erect stems from 
two to eight feet tall, small coriaceous obovate or orbicular leaves 
pale and coated below, like the young branchlets, with soft pubes- 
cence, staminate aments in the axils of lower leaves and below the 
pistillate aments, and oblong glabrous erect strobiles. An inhabit- 
ant of bogs, it is distributed from western Connecticut, New Jersey, 
