308 FLORA. 



Flowers solitary in the axil of each bract. Staminate flowers consisting 

 of from one to numerous stamens inserted on the receptacle, subtended 

 by a gland-like or cup-shaped disk; anthers 2-celled, the sacs longitudi- 

 nally dehiscent. Pistillate aments sometimes raceme-like; pistillate 

 llowers of a i-celled ovary subtended by a minute disk ; placentae 2-4, 

 parietal ; ovules usually numerous, anatropous ; stigmas 2-4, simple or 2-4- 

 cleft. Seeds small or minute, provided with a dense coma of long, mostly 

 white, silky hairs. Endosperm none. Cotyledons plano-convex. Radicle 

 short. The family includes only the 2 following genera, consisting of 200 

 species or more, mostly natives of the north temperate and arctic zones. 



Bracts fimbriate or incised ; stamens numerous. 1. Populus. 



Bracts entire ; stamens 2-10. 2. Salix. 



1. POPULUS L. 



Trees with scaly resinous buds, and usually long-petioled leaves, the stipules 

 minute, fugacious. Disk cup-shaped, oblique. Staminate aments dense, pendu- 

 lous. Staminate flowers with from 4 to 60 stamens, their filaments distinct. Pistillate 

 aments sometimes raceme-like through the elongation of the pedicels. Ovary ses- 

 sile; style short; stigmas 2-4, entire or 4-lobed. Capsule 2-4-valved. Coma of 

 the seeds often very long and conspicuous. [Name ancient, used for these trees by 

 Pliny.] About 25 species, natives of the northern hemisphere. Besides the follow- 

 ing, some 3 others occur in the western part of N. Am. 



Petioles terete or chanelled, scarcely or not at all flattened laterally. 



Leaves persistently and densely white-tomentose beneath, lobed or coarsely sinuate- 

 dentate. 1. P. alba. 

 Leaves glabrous or nearly so when mature, crenate. 



Foliage densely tomentose when young; capsule slender-pedicelled. 



2. P. heterophylla. 

 Foliage not tomentose; capsule short-pedicelled. 



Leaves broadly ovate, truncate or cordate at the base; petioles and nerves 



usually puberulent. 3. P. candicans. 



Leaves ovate to lanceolate, acute or obtuse at the base; petioles glabrous. 

 Leaves ovate or broadly lanceolate; petiole fully half as long as the blade. 

 Leaves green on both sides, abruptly acuminate. 



6. P. acuminata. 

 Leaves pale beneath, acute or somewhat acuminate. 



4. P. balsami/era. 

 Leaves lanceolate; petiole about one-third the length of the blade or less. 



5. P. angustifolia. 

 Petioles strongly flattened laterally. 



Leaves broadly deltoid, abruptly acuminate. 



Young leaves pubescent; capsule nearly sessile. 7. P. nigra. 



Young leaves not pubescent; capsule slender-pedicelled. 8. P. deltoides. 

 Leaves broadly ovate or suborbicular. 



Leaves coarsely sinuate-dentate. 9. P. grandidentata. 



Leaves crenulate-denticulate. 10. P. tremu/oides. 



1. Populus alba L. Abele. White or Silver-leaf Poplar. (I. F. f. 1164.) 

 A large tree, with smooth light gray bark, attaining a maximum height of about 35 

 m. and a trunk diameter of 1.5 m. Young foliage densely white-tomentose, the 

 leaves becoming glabrate and dark green above, broadly ovate or nearly orbicular in 

 outline, apex acute, base truncate or subcordate, 3-5 -lobed or irregularly dentate, 

 6-10 cm. long; petiole shorter than the blade; staminate aments 3-5 cm. long. In 

 yards and along roadsides, springing up from suckers of older trees, N. B. to Va. 

 Native of Europe and Asia. March-May. 



2. Populus heterophylla L. Swamp or Downy Poplar. (I. F. f. 1168.) 

 An irregularly branching tree, sometimes 25 m. high and with a trunk I m. in 

 diameter, the bark rough. Leaves long-petioled, broadly ovate, obtuse or subacute 

 at the apex, rounded, truncate or subcordate at the base, crenulate-denticulate, 12- 

 15 cm. loni^. or those of young plants much larger, glabrous or somewhat floccose 

 beneath when mature; bracts glabrous or nearly so; staminate aments stout, 7-10 

 cm. long, 18-25 mm. in diameter, drooping; stamens numerous; pistillate aments 



