Part 4

_a_ Leaves entire, sometimes 3 or 4-lobed. (_aa_, see p. xxiii). _b_ Stipules present. Juice milky. Maclura (p. 331). Juice watery. Stipules connate, enveloping the young leaves, their scars encircling the branchlet. Leaves acute or acuminate, entire; winter-buds pointed, nearly terete. Magnolia (p. 342). Leaves truncate, sinuately 4-lobed; winter-buds obtuse, compressed. Liriodendron (p. 351). Stipules distinct. Branches spinescent; leaves glandular, caducous (_crenately serrate on vigorous shoots_). Dalea (p. 621). Branches not spinescent; leaves without glands. Winter-buds with a single pair of connate scales. Salix (p. 138). Winter-buds with several pairs of imbricate scales. Branchlets without a terminal bud; leaves 3-nerved. Celtis (p. 318). Branchlets with a terminal bud, leaves penniveined. Quercus sp. 17—20 (p. 262). _bb_ Stipules wanting. _c_ Branchlets bright green and lustrous for the first 2 or 3 years; leaves sometimes 3-lobed, aromatic. Sassafras (p. 362). _cc_ Branchlets brown or gray. _d_ Leaves acute or acuminate. Leaves 10′—12′ long, obovate-oblong, acuminate, glabrous, emitting a disagreeable odor. Asimina (p. 353). Leaves smaller. Petioles very slender, 1′—2′ long; leaves elliptic, acuminate. Cornus alternifolia (p. 789). Petioles short. Branchlets with a terminal bud. Leaf-scars about as long as broad; branchlets without lenticels, light reddish brown. Elliottia (p. 791). Leaf-scars crescent-shaped, broader than long, with 3 distinct bundle-traces. Leaves pubescent on both sides, rugulose above; petioles 1′—2′ long, like the young branchlet densely pubescent. Leitneria (p. 167). Leaves glabrous and smooth above, glabrous or pubescent below; petioles and branchlets usually glabrous or nearly so at maturity. Nyssa (p. 779). Branchlets without a terminal bud. Pubescence consisting of simple hairs or wanting. Leaves 4′—6′ long, pubescent beneath while young; branchlet light brown or gray. Diospyros virginiana (p. 821). Leaves 1½′—3′ long, glabrous; branches light yellowish gray. Schœpfia (p. 336). Pubescence stellate; leaves obovate or elliptic, 2½′—5′ long, pubescent below. Styrax (p. 829). _dd_ Leaves obtuse or acute. Branchlets not spinescent. Leaves glabrous at maturity, their petioles slender. Cotinus (p. 657). Leaves pubescent below at maturity; their petioles short and thick. Diospyros texana (p. 823). Branchlets spinescent; leaves often fascicled on lateral branchlets. Bumelia (p. 812). _aa_ Leaves serrate or pinnately lobed. _b_ Stipules present. (_bb_, see p. xxvi.) _c_ Winter-buds naked. Leaves oblique at base, the upper side rounded or subcordate, obovate, coarsely toothed. Hamamelis (p. 368). Leaves equal at base, cuneate, finely serrate or crenate. Rhamnus sp. 2, 3 (p. 724, 725). _cc_ Winter-buds with a single pair of connate scales. Primary veins arching and uniting within the margins; leaves simply serrate or crenate, sometimes entire. Salix (p. 138). Primary veins extending to the teeth, leaves doubly serrate, often slightly lobed. Alnus (p. 220). _ccc_ Winter-buds with several pairs of imbricate scales. _d_ Terminal buds wanting; branchlets prolonged by an upper axillary bud. Juice milky; leaves usually ovate, often lobed. Morus (p. 328). Juice watery; leaves not lobed. Leaves distinctly oblique at base. Leaves with numerous prominent lateral veins. Leaves generally broad-ovate, simply serrate, stellate-pubescent at least while young, rarely glabrous. Tilia (p. 732). Leaves never broad-ovate, usually doubly serrate, more or less pubescent with simple hairs, at least while young. Winter-buds ovoid, usually acute, ⅓ to nearly as long as petioles; leaves 1′—7′ long, doubly serrate. Ulmus (p. 309). Winter-buds subglobose, minute; leaves 2′—2½′ long, crenate-serrate. Planera (p. 316). Leaves 3 or 4-nerved from the base. Celtis (p. 318). Leaves slightly or not at all oblique at base. Leaves 3-nerved from the base, glandular-crenate or glandular-serrate. Ceanothus (p. 726). Leaves not or obscurely 3-nerved at base, usually doubly serrate. Leaves blue-green; petioles ¼′—½′ long; bark smooth, gray-brown. Carpinus (p. 201). Leaves yellow-green. Bark rough, furrowed; petioles ⅛′—¼′ long; leaves not resinous-glandular. Ostrya (p. 202). Bark flaky or cherry-tree like; petioles ¼′—1′ long; leaves often resinous-glandular while young. Betula (p. 205). _dd_ Terminal buds present. Primary veins arching and uniting within the margin (_extending to the margin in the lobed leaves of Malus_). Winter-buds resinous; leaves crenate, usually truncate at base; petioles slender. Populus (p. 119). Winter-buds not resinous. Leaf-scars with 3 bundle-traces. Leaves involute in bud, often lobed on vigorous shoots; winter-buds obtuse, short, pubescent. Malus (p. 379). Leaves conduplicate (_or in some species of Prunus convolute_), never lobed; winter-buds acute. Winter-buds elongated; branches never spinescent. Amelanchier (p. 393). Winter-buds not elongated, ovoid; branches sometimes spinescent. Prunus (p. 555). Leaf-scars with 1 bundle-trace; leaves simply serrate. Ilex sp. 5—6 (p. 673).

Primary veins extending to the teeth or to the lobes. Leaves lobed. Quercus sp. 1—16, 35—50 (p. 241, 283). Leaves serrate-toothed. Winter-buds with numerous scales. Leaves lustrous beneath, remotely serrate or denticulate; winter-buds elongated, acuminate. Fagus (p. 228). Leaves pale beneath, coarsely dentate or serrate; winter-buds acute. Chestnut Oaks. Quercus sp. 51—54 (p. 303). Winter-buds with 2 pairs of scales. Castanea (p. 230). Leaves doubly or simply serrate, or lobed, with serrate lobes; branches often furnished with spines. Leaves involute in the bud; branchlets often ending in blunt spines. Malus (p. 379). Leaves conduplicate in the bud; branches usually armed with sharp-pointed single or branched axillary spines. Cratægus (p. 397). _bb_ Stipules wanting. _c_ Leaves not lobed. Leaves subcoriaceous, oblong, sometimes nearly entire, glabrous. Symplocos (p. 831). Leaves thin. Leaves oblong-obovate, acute, pubescent beneath. Gordonia alatamaha (p. 752). Leaves oblong or lanceolate, acuminate, glabrous or puberulous while young, turning scarlet in the autumn. Oxydendrum (p. 796). Leaves ovate to elliptic, stellate-pubescent or glabrous, turning yellow in the autumn. Halesia (p. 824). _cc_ Leaves palmately lobed. Stipules large, foliaceous, united; branchlets without a terminal bud. Platanus (p. 371). Stipules small, free, caducous; branchlets with a terminal bud. Liquidambar (p. 367).

†† Leaves inconspicuous or wanting; branches spiny or prickly.

Branches or stems succulent, armed with numerous prickles. Branches and stems columnar, ribbed, continuous; leaves 0. Cereus (p. 757). Branches jointed, tuberculate; leaves scale-like. Opuntia (p. 759). Branches rigid, spinescent. Leaves minute, narrow-obovate. Branchlets bright green. Kœberlinia (p. 754). Branchlets red-brown. Dalea (p. 621). Leaves scale-like, caducous. Canotia (p. 677).

2. Leaves compound.

* Leaves 3-foliolate, without stipules.

Leaves persistent; leaflets obovate, entire, sessile. Hypelate (p. 716). Leaves deciduous. Leaflets deltoid to hastate, entire, rounded at apex; branches prickly. Erythrina (p. 627). Leaflets ovate to oblong, acuminate, strongly scented and bitter; branches unarmed. Ptelea (p. 639).

** Leaves twice pinnate; stipules present.

_a_ Leaves unequally twice pinnate, 2°—4° long, deciduous; leaflets serrate, 2′—3′ in length; branches and stem armed with scattered prickles. Aralia (p. 778). _aa_ Leaves equally twice pinnate, usually smaller; branches unarmed or armed with stipular or axillary spines (in _Parkinsonia_ often apparently simply pinnate). _b_ Leaflets crenate; leaves simply or twice-pinnate on the same plant, deciduous, usually armed with simple or branched axillary spines. Gleditsia (p. 607). _bb_ Leaflets entire. Leaflets 2—2½′ long; leaves deciduous; branchlets stout, unarmed. Gymnocladus (p. 605). Leaflets smaller; leaves usually persistent; branchlets slender. Branches armed with prickles or spines. Leaves with 2 or rarely 4 pinnæ. Branches armed with axillary spines or spiny rachises. Pinnæ with 4—8 leaflets; branches with short axillary spines. Cercidium (p. 613). Pinnæ with 8—60 leaflets; branches armed with spiny rachises or rigid branchlets terminating in stout spines. Parkinsonia (p. 611). Branches armed with stipular prickles; leaves persistent. Pinnæ with many oblong to linear leaflets. Prosopis (p. 599). Pinnæ with 1 pair of orbicular to broad-oblong leaflets. Pithecolobium unguis-cati (p. 586). Leaves with 6, or more, rarely 4, pinnæ. Prickles usually spreading, often recurved. Acacia (p. 591). Prickles usually more or less ascending, straight. Pithecolobium (p. 586). Branches unarmed. Branchlets and petioles glabrous; leaves with 2—5 pair of pinnæ, each with 40—80 leaflets. Lysiloma (p. 589). Branchlets and petioles pubescent while young; leaves with 5—17 pair of many-foliolate pinnæ, or pinnæ 2—4 and each with 8—16 leaflets. Leucæna (p. 596).

*** Leaves simply pinnate.

_a_ Leaves equally pinnate. Stipules wanting. Leaflets 2—4, generally oblong-obovate. Exothea (p. 714). Leaflets 6—12. Leaflets obtuse, usually oblong-obovate. Leaflets 8—12, 2′—3′ long, pale below; leaves occasionally opposite. Simarouba (p. 642). Leaflets 6—8, 1′—1½′ long, green below. Xanthoxylum coriaceum (p. 637). Leaflets 6—8, acuminate. Swietenia (p. 648). Stipules present. Branches armed with infra-stipular spines in pairs; leaflets 10—15, usually oblong-obovate, ½′—¾′ long, persistent. Olneya (p. 626). Branches unarmed; leaflets 20—46, ovals ½′—⅔′ long. Eysenhardtia (p. 620). _aa_ Leaves unequally pinnate. _b_ Stipules present. Leaflets sharply serrate; leaves deciduous; winter-buds resinous. Sorbus (p. 390). Leaflets entire or crenately serrate. Leaves deciduous. Leaflets 7—11, 3′—4½′ long; branches unarmed. Leaflets usually alternate, thin and glabrous at maturity. Cladrastis (p. 618). Leaflets opposite, coriaceous, pubescent beneath at least along the veins. Ichthyomethia (p. 628). Leaflets 9—21, 1—2 cm. long. Branches usually with stipular prickles, sometimes viscid. Robinia (p. 622). Branches unarmed, not viscid; leaflets 13—19, elliptic. Sophora affinis (p. 617). Leaves persistent. Leaflets 7—9, oblong-elliptic, 1′—2½′ long; branches unarmed. Sophora secundiflora (p. 616). Leaflets 10—15; branches prickly. Olneya (p. 626). _bb_ Stipules wanting. _d_ Leaves persistent. Leaflets long-stalked (_sometimes nearly sessile in Xanthoxylum flavum_). Leaflets oblong-ovate, cuneate at base. Leaflets acuminate, glabrous. Picramnia (p. 643). Leaflets obtuse, tomentose when unfolding. Xanthoxylum flavum (p. 636). Leaflets broad-ovate, usually rounded or subcordate at base. Metopium (p. 658). Leaflets sessile or nearly so. Petiole and rachis winged. Leaflets crenate, obovate, about ½′ long; branches prickly. Xanthoxylum Fagara (p. 634). Leaflets entire. Leaflets oblong, usually acute, 3′—4′ long. Sapindus saponaria (p. 712). Leaflets spathulate, rounded at apex, not more than ¾′ long. Pistacia (p. 656). Petiole and rachis not winged. Leaflets 7—19, acuminate, 2′—5′ long. Sapindus marginatus (p. 713). Leaflets 21—41, obtuse, ½′—¾′ long. Alvaradoa (p. 644). _dd_ Leaves deciduous. Leaflets long-stalked, 3—7, entire, acute. Bursera (p. 645). Leaflets sessile or nearly so. Branches prickly; leaflets crenate. Xanthoxylum clava-Herculis (p. 635). Branches unarmed. Juice milky or viscid; leaflets serrate or entire; rachis sometimes winged. Rhus species 1—3 (p. 660). Juice watery. Rachis without wings. Leaflets entire, acuminate, 7—9. Sapindus Drummondii (p. 714). Leaflets serrate or crenate. Winter-buds large; leaflets 5—23, aromatic. Winter-buds naked. Juglans (p. 169). Winter-buds covered with scales. Carya (p. 176). Winter-buds minute, globose, scaly; leaflets 5—7, ovate, not aromatic. Ungnadia (p. 717). Rachis winged; leaflets 10—20, entire, rounded at apex, not more than ¼′ long. Bursera microphylla (p. 647).

TREES OF NORTH AMERICA (Exclusive of Mexico)

Class 1. GYMNOSPERMÆ.

Ovules and seeds borne on the face of a scale, not inclosed in an ovary; resinous trees, with stems increasing in diameter by the annual addition of a layer of wood inside the bark.

I. PINACEÆ.

Trees, with narrow or scale-like generally persistent clustered or alternate leaves and usually scaly buds. Flowers appearing in early spring, mostly surrounded at the base by an involucre of the more or less enlarged scales of the buds, unisexual, monœcious (_diœcious in Juniperus_), the male consisting of numerous 2-celled anthers, the female of scales bearing on their inner face 2 or several ovules, and becoming at maturity a woody cone or rarely a berry. Seeds with or without wings; seed-coat of 2 layers; embryo axile in copious albumen; cotyledons 2 or several. Of the twenty-nine genera scattered over the surface of the globe, but most abundant in northern temperate regions, thirteen occur in North America.

CONSPECTUS OF THE NORTH AMERICAN GENERA.