FAMILY SALICACEÆ

Genus POPULUS

QUICK-GROWING trees with angled or round twigs, set with scaly buds, soft, light wood, and bitter bark. Leaves deciduous, simple, alternate, usually broad, on long petioles. Flowers diœcious, both kinds in crowded, pendulous catkins; each flower subtended by a bract with deeply cut, hairy margin. Fruit pendulous racemes of 2 to 4-valved pods; seeds minute, with dense, silky float attached.

KEY TO SPECIES

A. Leaf stalks flattened.

B. Buds smooth, resinous.

C. Leaves triangular, coarsely serrate.

D. Blades of leaves 3 to 5 inches long: (P. deltoidea) COTTONWOOD

DD. Blades of leaves 2 to 2 ½ inches long.

E. Twigs slender, pubescent, yellow: (P. Fremontii) COTTONWOOD

EE. Twigs stout, smooth, orange: (P. Wislizeni) COTTONWOOD

CC. Leaves roundish, finely serrate: (P. tremuloides) QUAKING ASP

BB. Buds downy; leaves ovate, coarsely toothed: (P. grandidentata) GREAT-TOOTHED ASPEN

AA. Leaf stalks round; buds resinous.

B. Foliage green on both sides.

C. Shape of leaves lanceolate: (P. angustifolia) NARROW-LEAVED COTTONWOOD

CC. Shape of leaves rhombic or deltoid, with long-pointed apex.

D. Margins finely serrate: (P. acuminata) LANCE-LEAVED COTTONWOOD

DD. Margins coarsely and crenately toothed. (P. Mexicana) MEXICAN COTTONWOOD

BB. Foliage pale, silvery or rusty below; margins finely serrate.

C. Buds thickly covered with yellow resin: (P. balsamifera) BALM OF GILEAD

CC. Buds somewhat resinous.

D. Bark pale grey: (P. trichocarpa) BLACK COTTONWOOD

DD. Bark reddish brown: (P. heterophylla) SWAMP COTTONWOOD

Trees of the genus Populus form extensive forests in low, rich land and on high slopes of mountains. They attain large size, are quick of growth, and have exceeding tenacity of life, striking roots from twigs and sending up suckers from underground. Seeds are also a reliable means of reproduction, as they are produced in great numbers, and are widely scattered by the wind. The wood is one of the best materials for pulp making, and for a multitude of cheap wares for which a wood easy to work is demanded. The trees are largely planted for shade and ornament, for windbreaks, and to hold the banks of streams.

There are twenty-five species of Populus known, eleven of which are native to America. European species are often planted in this country, where they usually thrive as if at home. Some Russian varieties are successful on the Western prairies. China and Japan each have representative poplars here.

Cottonwood (Populus deltoidea, Marsh.)—Much-branched tree, 60 to I50 feet in height; diameter 5 to 7 ½ feet. Bark deeply furrowed, grey-brown, becoming greenish; often ashen grey on old trees. Wood dark brown; sap wood white; weak, compact, light. Buds large, pointed, resinous. Leaves broadly ovate, taper pointed, 3 to 5 inches long, margin wavy and coarsely toothed, thick, shining, paler beneath, yellow in fall; petiole long, slender, flat, red or yellow. Flowers, March, in pendant catkins, 3 to 5 inches long, loosely flowered; staminate red, numerous; pistillate green, sparse on trees. Fruits, May, aments 6 to 12 inches long; capsules ovate, often curved, 2-valved; seeds in white, cottony mass. Preferred habitat, moist soil along streams. Distribution, Quebec to Northwest Territory; south to Florida; west to Colorado and New Mexico. Uses: Much planted for shade and windbreaks in the prairie states. Wood has recently come into use in making packing cases.

We all concede that the cottonwood has faults. The brittle wood cannot withstand the winds, the leaves drop untidily through the summer, the cast-off staminate catkins are a nuisance in spring, and the fluffy cottony seeds shed so deliberately in early summer by the fertile trees fill the air and the meshes of door and window screens to the exasperation of the whole neighbourhood.

But go out into one of the little breathing spaces called parks in a great city like New York in the early spring days when the children of the tenements and the stuffy flats are brought out for a first breath of the spring air. The old cottonwood has its buds all a-glisten with promise, and in a few days longer the dainty little leaves twinkle all over the treetop with the most cheerful green. In the late summer, in spite of its losses, the tree still carries a bright green crown of shade which turns yellow before it falls. With all its faults, it endures the heat of cities, and the dust and soot with commendable patience. In the protection of great buildings it does not suffer by winds as it does in exposed situations.

There are better, longer-lived trees for the open country, but in cities the cottonwood has a use and a message of cheer for rich and poor who look up and learn to know the tree. Unlike the variety next described, the cottonwood takes on dignity with added years.

The Carolina Poplar, considered a variety (Carolinensis) of the cottonwood above, is a strict pyramidal tree of vigorous and surprisingly rapid growth. In cities the varnish on the leaves evidently protects them from dust and smoke. Nurserymen have exploited this tree in America and Europe far beyond its merits, for though useful as a temporary tree, giving shade very soon, poplars should give way gradually to more permanent species planted with them. This poplar soon outgrows the beauty and luxuriance of its youth, and becomes broken and ugly. The immoderate planting of these trees gives a cheap character to many an otherwise handsome town or country place. New summer resorts and city “additions” show poplars in great numbers about their premises. The “poplar habit” is a very short-sighted one and expensive in the long run. J. Wilkinson Elliott, of Pittsburg, persuades his clients to plant Balm of Gilead, a much more satisfactory species.

The Cottonwood (P. Fremontii, Wats.) grows in western California, from Sacramento south, and eastward to Colorado and Texas. It is a favourite shade tree, and an important source of fuel. Cut back systematically, the trees produce abundant crowns of suckers in a very short time.

Frémont’s cottonwood is distinguishable from the preceding species by the smaller size of its leaves and the pubescence of its buds. Its leaves are sometimes kidney shaped. The bark of old trees is reddish brown. The trees reach 100 feet in height.

The Cottonwood (P. Wislizeni, Sarg.) of the Rio Grande Valley in Texas and New Mexico, is a large, wide-crowned tree with stout, smooth, orange-coloured twigs and leathery, yellow-green leaves. Without these distinguishing characters it might easily be confused with the two species last described. The tree is not met with outside its natural range.

Aspen, or Quaking Asp (Populus tremuloides, Michx.) Slender tree, 40 to 80 feet high, with angular, scarred twigs, and large, vigorous roots. Bark rough, dark on base of trunk, be coming pale greenish brown or nearly white, and marked with broad, dark bands below the limbs. Wood light brown, sap wood white, soft, close grained, light, weak, not durable. Buds waxy, conical, scaly, brown. Leaves alternate, simple, 1½ to 2 ½ inches long, ovate or almost round, with straight base and apex acute; margin faintly toothed; thin, shining green above, dull yellow-green beneath; autumn colour yellow; petiole flattened, flexible, slender. Flowers in April, diœcious ; catkins pendulous, 1½ to 2 ½ inches long, each flower on notched bract, fringed with hairs; stamens 6 to 12 on disc; ovary conical; stigmas 2-lobed; disc broad, persistent. Fruits, May, borne in drooping aments, 4 inches long; capsules oblong-conical, 2-valved, pale green; seeds oblong, covered with brush of long white hairs. Preferred habitat, sandy or gravelly soil, dry or moist. Distribution, Newfoundland to Hudson Bay and Alaska; south to New Jersey, Pennsylvania, Kentucky, Nebraska; also high altitudes throughout the Rocky Mountains and coast ranges. Uses: Most valuable cover for forest land devastated by fire. Comes up from seed scattered broadcast by wind, and acts as nurse to hardwoods and conifers that later succeed them. A pretty shade and ornamental tree, though short lived.

Aspen is a general term applied to trees of this genus whose leaves have flattened stems. The round-stemmed ones are poplars, proper. The Russian adage: “There is a tree that trembles without even a breath of wind,” might well fit this most apprehensive of all the aspen trees. Its dainty round leaf blades twinkle in the sun, a grove of the trees together producing at a little distance the appearance as well as the sound of rippling water. It is the gayest of trees. That was a lugubrious wight who imagined it accursed by being the tree on which Judas Iscariot hanged himself, and doomed “ever afterward to shudder and tremble on account of its connection with the tragedy of Calvary.” The same legend attaches to the pretty little redbud, the Judas tree.

“The green wood moved, and the light poplar shook
Its silver pyramid of leaves.”

We might easily adapt these graceful lines to our quaking asp, but that the word “silver” will not apply accurately. The English poet, Barry Cornwall, was describing the white poplar with white leaf linings.

There is no mystery in the trembling of these aspen leaves. Examine one. The stem is long and flexible. It is flattened in a plane at right angles with the blade of the leaf. Now, given a leaf that is dangling from its twig, and has four flat surfaces exposed, it is a cautious breeze indeed that is able to get by without disturbing the leaf’s unstable equilibrium. Given, a treetop of leaves similarly made and hung, and you have a quaking asp. It waves you an invitation to examine, and see if the explanation above is not correct.

Homer’s famous simile based on the leaves of poplar trees is not ungallant as that of Gerarde, who compares them to “women’s tongues which seldom cease wagging.”

The most delicate colouring is found in this aspen. The pale bark takes on a cool, greenish tinge in earliest spring The furry catkins flush pink with their silvery grey silk. The opening leaves unroll, soft and white, like flannel—“ju’ luk a kitten’s ear,” each one of them, to quote Uncle Eb. They pass rough various tones of rose and olive on the way to their lustrous adult stage. Every day from early March till May it is worth while to go by a copse of trembling aspen and look up to see what new phase of the trees’ life history has opened since last we passed that way.

Large-toothed Aspen (Populus grandidentata, Michx.) Narrow, round-headed tree, 50 to 75 feet high, with stout, angular branchlets, roughened by leaf scars. Bark dark brown and deeply fissured between broad ridges on old trunks; grey-green on limbs. Twigs smooth, pubescent at first. Wood soft, weak, pale brown; sap wood white. Buds ovate, pointed, scaly, waxed. Leaves ovate to roundish, heart shaped at base, acute, with sparse, irregular-rounded teeth; 3 to 4 inches long, 2 to 3 inches wide, thick,  green, with pale somewhat tomentose linings; petioles slender, laterally flattened, 2 to 3 inches long. Flowers, April, diœcious, in pendulous catkins, 2 to 3 inches long; staminate red from anthers; pistillate green from spreading stigmas; bracts deeply cleft. Fruits, hairy capsules, 2-valved, thin walled, slender, crooked, filled with minute seeds, each with white, hairy float; May. Preferred habitat, rich, sandy loam, on borders of streams. Distribution, Nova Scotia to Minnesota; south to New Jersey, and on Alleghanies to North Carolina, Tennessee and Kentucky.

The coarse, thick leaves with large, rounded teeth on the margins, distinguished this great-toothed aspen from its dainty cousin, the quaking asp, with which it is often associated in the woods. In fact, the tree is coarser throughout, the branchlets stout and the buds downy, so no one who is interested and observant will have any trouble to tell them apart.

The Narrow-leaved Cottonwood (P. angustifolia, James) has lanceolate leaves, more like a willow’s than a poplar’s. The margins are finely saw toothed, the petioles short, and the texture thin and firm. It is easy to see that the tree is a poplar, the flattened petiole alone being a sufficient clue. The tree lines the banks of mountain streams of the Rockies, 5,000 to 10,000 feet in elevation. It grows from 40 to 60 feet high, a narrow pyramid of slender limbs.

The Lance-leaved Cottonwood (P. acuminata, Rydb.), with scarcely wider leaves than the preceding species, is a compact, round-headed little tree that grows on stream borders and arid foothills of the Rocky Mountains from British Columbia to southern Nebraska and Colorado. Its distribution is not fully ascertained. It is used for fuel and planted for shade in communities within its natural range.

The Mexican Cottonwood (P. Mexicana, Wesm.) grows, a graceful, wide-spreading tree of medium size, along mountain streams near the Mexican border of Arizona and New Mexico. Its rhombic, long-pointed leaves are very coarsely toothed, and when they first unfold are dark red, soon becoming yellow-green and leathery. The bark is grey or almost white.

Balm of Gilead (Populus balsamifera, Linn.)—Large tree with stout trunk, 75 to 100 feet high. Bark grey, broken into broad ridges; branches greenish, smooth or with warty outgrowths. Wood pale, soft, compact, weak, light brown. Buds long, slender, shining with yellow wax. Leaves broadly ovate, acute, finely and bluntly toothed, thick, shining, dark green, pale often rusty beneath, 3 to 5 inches long; petioles slender; autumn colour yellow. Flowers, March, before leaves; aments drooping, hairy; stamens 18 to 30, crowded on disc; anthers pale red; pistils green with spreading stigmas; flowers scattered. Fruits, May, capsules scattered on stems 4 to 6 inches long; seed brown, buried in cottony float. Preferred habitat, moist or dry soil near water. Distribution, Newfoundland to Hudson Bay and Alaska; south to Maine, New York, Michigan, Nebraska, Idaho and British Columbia. Uses: Well worthy of planting for shade, ornament and shelter.

The fragrant wax that saturates the winter buds and coats the young leaves in spring gives this tree its name. The bees find it as soon as the sap stirs and the wax softens. Quantities of it are collected and stored in hives “against a rainy day”; for this is what bees use to seal up cracks in their hives. It is known to bee keepers as “propolis.” The service this wax renders the tree is to prevent the loss of water from the buds, and the absorption of more, after they are ready for winter. It is not “to keep the buds from freezing,” as some people fondly imagine. The buds freeze solid, but it does them no harm. They are adjusted to it. In the far North the Indian uses the balsam of Balm of Gilead trees to seal up the seams of his birch-bark canoe, and of dishes and other utensils made of the same material.

The forests of Balm of Gilead stretch away over the lake margins and bottom lands of upper Canada, the largest and most prominent feature of vegetation in the vast regions that approach the Arctic circle, and extend down into the northern tier of states, from ocean to ocean.

The chief interest that centres about the tree is its good record when planted as a shade and ornamental tree, and in shelter belts. It is a hardy tree of excellent habit, compact and erect, but not too narrow for shade. It is easily propagated and transplanted, and grows rapidly. The tree is handsome, winter and summer. It has all the good points of the Carolina poplar, and lacks its fault of becoming so soon an unsightly cripple.

The Black Cottonwood (P. trichocarpa, Hook.) is the giant of the genus, reaching 200 feet in height and 7 to 8 feet in trunk diameter. It is tall and stately, with a broad, rounded crown supported upon heavy upright limbs. One of the beautiful sights of the Yosemite Park is the autumnal gold of black cottonwood groves whose abundant foliage embowers the stream borders at the altitude of about 4,000 to 5,000 feet. The tree’s range covers the coast plain and western slopes of mountains from Alaska to southern California. The largest trees are on the lowest levels. The dark rich green of the leaves gives this tree its name. They are ovoid, 3 to 4 inches long, with the finest of saw-toothed margins. The wood has come into extensive use for the manufacture of various woodenwares and for staves of sugar barrels.

Swamp Cottonwood (Populus heterophylla, Linn.)—Round- topped tree, 50 to 90 feet high. Bark red-brown, in narrow, loose plates; twigs red or grey, containing orange pith. Wood brown, light, compact. Buds resinous, ovate, with red scales. Leaves broadly ovate, 4 to 7 inches long, serrate, dark green with pale lining, when mature, covered with white tomentum as they unfold; petioles round, slender; yellow or brown in autumn. Flowers, March or April; staminate aments crowded, erect until blossoms open; anthers deep red; pistillate aments few-flowered, drooping. Fruit, May, aments 4 to 6 inches long; capsules few, 2 to 3-valved, ½ inch long, bell shaped. Preferred habitat, wet soil. Distribution, swamps from southern Connecticut to Georgia and Louisiana; north along Mississippi to Arkansas and Indiana.

The swamp cottonwood is variable in the base, apex and margin of its leaf. It may exhibit coarse or fine saw teeth, a blunt or sharp-pointed apex, a square or heart-shaped base. The conspicuous netted veins are always present, and the leaves are always large and broadly ovate, with slim, round petioles. The orange-coloured pith of the branchlets best distinguishes the tree from other poplars. The new shoots and the unfolding leaves are coated with white down. It often takes a whole summer to get rid of it.

The Acadians (probably) are responsible for the name langues de femmes, by which the tree is known in Louisiana. The mild calumny of Gerarde is thus perpetuated and extended to a species whose leaf stems are merely flexible, not flat at all! In the lumber trade the wood is known as “black poplar.” It is dark brown in colour.

THREE EUROPEAN POPLARS IN CULTIVATION IN AMERICA

A. Leaves bright green, lined with white down, irregularly lobed and toothed: (Populus alba) ABELE or SILVER-LEAVED POPLAR

AA. Leaves dark green on both sides, smooth, broad as long, finely and regularly toothed; apex tapering.

B. Shape broadly pyramidal. (Populus nigra) BLACK POPLAR

BB. Shape narrowly pyramidal (P. migra, var. Italica) LOMBARDY POPLAR

The Abele or White Poplar (Populus alba, Linn.) is much planted about American homes, its downy-leaved and “maple- leaved” varieties having the preference. The silvery velvet of the leaf linings is in sharp contrast to the dark, shining upper surfaces of the leaves. The flexible stems give the wind much freedom in the treetops, and the sunlight is reflected from the leaves much as it is on rippling water. The pale outer bark breaks in streaks and spots, showing the dark under layers, much as the palest trunks of cottonwoods do. The tree is distinctly a poplar in flowers and fruits.

Two bad habits have these silvery poplars: (1) their roots send up suckers, to the distress of owners and neighbours; 2) their leaves accumulate and hold dust and coal soot until they are filthy before the summer is half done. Moral: Plant your silver poplar in the background, where its sprouting can be controlled without damage to the lawn and where distance lends enchantment to the view of its foliage.

The Black Poplar (P. nigra, Linn.), of Europe and Asia, Has become established in certain parts of the Eastern States, but it is now chiefly met with in its cultivated forms. Variety elegans is a dainty tree with small, bright, twinkling leaves and ruddy twigs and petioles. The following variety is much more extensively known, though it has less horticultural merit.

The Lombardy Poplar (Populus nigra, var. Italıca) is the exclamation point that marks by its soldierly rows so many familiar boundary lines of farms and village properties. It has the merit of infringing but slightly even by its shade on the rights and premises of others. Indeed, that such a tree should be planted for the shade it gives is scarcely probable. The pencil- like form and the twinkling of the green leaves are attractive. Italian villas were punctuated with them, and any piece of planting may well be diversified and accented by a group of these trees. But they need to be flanked by trees of diffuse habit—never set alone or in rows! The great fault of these poplars is the early dying of their limbs, because of much crowding. The tree retains these dead limbs, and so loses its youthful beauty and becomes scraggy topped. As the scientific name points out, these trees are an Italian variety of the black poplar.