SALICACE^ 153 



globose or ovate-oblong, cylindrical or slightly lobed, with 2 or 3 or rarely 4 placentas ; 

 styles usually short; stigmas as many as the placentas, divided into liliform lobes 

 or broad, dilated, 2-parted or lobed. Fruit ripening before the full growth of the 

 leaves, greenish, reddish brown, or buff color, oblong-conical, subglobose or ovate- 

 oblong, separating at maturity into 2-4 recurved valves. Seeds broadly obovate or 

 ovate, rounded or acute at the apex, light chestnut-brown; cotyledons elliptical. 



Populus in the extreme north often forms great forests, and is common on the 

 alluvial bottom-lands of streams and on high mountain slopes, ranging from the 

 Arctic Circle to northern Mexico and Lower California and from the Atlantic to 

 the Pacific in the New World, and to northern Africa, the southern slopes of the 

 Himalayas, central China, and Japan in the Old World. Of the twenty-five species 

 now generally recognized eleven are found in North America. The wood of many 

 of the American species is employed in large quantities for paper-making, and 

 several species furnish wood used in construction and in the manufacture of small 

 articles of woodenware. The bark contains tannic acid and is used in tanning 

 leather and occasionally as a tonic, and the fragrant balsam contained in the buds 

 of some species is occasionally used in medicine. The rapidity of their growth, their 

 hardiness and ease with which they can be propagated by cuttings, make many of 

 the species useful as ornamental trees or in wind-breaks, although planted trees 

 often suffer severely from the attacks of insects boring into the trunks and branches. 

 Of the exotic species, the Abele, or White Poplar, Populus alba, L., of Europe and 

 western Asia, and its fastigiate form, and the so-called Lorabardy Poplar, a tree of 

 pyramidal habit and a form of the European and Asiatic Populus nigra, L., have 

 been largely planted in the United States. 



Populus, of obscure derivation, is the classical name of the Poplar. 



CONSPECTUS OF THE NORTH AMERICAN SPECIES. 



Stigmas 2, 2-lobed, their lobes filiform ; capsule oblong'-conical, thin-walled, 2-valved ; 

 leaf-stalks elongated, compressed laterally ; buds slightly resinous. 



Leaves ovate or semiorbicular, short-pointed, slightly cordate or truncate at the base, 

 finely serrate ; buds usually glabrous. 1, P. tremuloides (AB, F, G). 



Leaves broadly ovate, coarsely crenate ; buds tomentose. 



2. P. grandidentata (A). 

 Stigmas 2-4, 2-lobed and dilated, the lobes variously divided ; capsule subglobose to ovate- 

 oblong, usually thick- walled, 2-4-valved ; buds resinous. 

 Leaf-stalks round. 



Leaves broadly ovate, acute, short-pointed or rounded at the apex, erenately serrate. 



3. P. heterophylla (A, C). 

 Leaves ovate-lanceolate, acute or acuminate, dark green and lustrous on the iipper 

 surface, pale and often rusty on the lower. 



4. P. balsamifera (AB, F, G). 



Leaves ovate or lanceolate, green on both surfaces. 5. P. angustifolia (F). 



Leaves rhomboid-lanceolate, long-pointed, green on both surfaces. 



6. P. acuminata (F). 



Leaves usually broadly ovate, acuminate, rounded or cordate at the broad base, dark 



green on the upper surface, pale, rusty, or silvery on the lower ; ovary tomentose. 



7. P. trichocarpa (B, G). 

 Leaves rhombic to broadly deltoid, elongated, acute or acuminate, green on both 

 surfaces. 8. P. Mexicana (H). 



Leaf-stalks compressed laterally. 

 Pistillate flowers on short pedicels. 



