GENUS i. 



WILLOW FAMILY. 



5. Populus acuminata Rydberg. Black 

 Cottonwood. Fig. 1444. 



P. acuminata Rydberg, Bull. Torr. Club 20: 50. 1893. 



Populns coloradeiisis Dode, Mem. Soc. Hist. Nat. Autun 

 18: [reprint 58]. 1905. 



A slender tree, with terete twigs, reaching ap- 

 proximately the dimensions of the preceding species, 

 the crown broadly pyramidal with spreading branches, 

 the foliage glabrous. Leaves rhomboid-lanceolate, 

 spreading or drooping, drying green, abruptly or 

 gradually long-acuminate at the apex,^ cuneate, 

 obtuse or rounded at the base, 2'-6' long, \'-2\' wide, 

 crenulate or the base entire; petioks slender, 1-21 

 long; staminate aments about ii' long; pistillate 

 aments slender, drooping, 3'-$' long; capsules ovoid, 

 obtuse, distinctly pedicelled. 



Borders of lakes and streams, North Dakota to As- 

 siniboia, western Nebraska, New Mexico and Nevada. 

 April-May. 



6. Populus heterophylla L. Swamp or Downy Poplar. Fig. 1445. 



Populus heterophylla L. Sp. PI. 1034. 1753. 



An irregularly branching tree, sometimes 80 high 

 and with a trunk 3 in diameter, the bark rough. 

 Young foliage densely tomentose. Leaves long- 

 petioled, broadly ovate, obtuse or subacute at the 

 apex, rounded, truncate or subcordate at the base, 

 crenulate-denticulate, s'-6' long, or those of young 

 plants much larger, glabrous or somewhat floccose 

 beneath when mature; petioles terete; bracts gla- 

 brous or nearly so ; staminate aments stout, 3'-4' 

 long, 9"-! 2" in diameter, drooping; stamens nume- 

 rous; pistillate aments raceme-like, peduncled, erect 

 or spreading, loosely flowered ; capsules ovoid, acute, 

 2-valved, 4"-6" long, shorter than or equalling their 

 pedicels. 



In swamps, Connecticut to Georgia, west to Louisiana, 

 north in the Mississippi Valley to Ohio, Indiana, Mis- 

 souri and Arkansas. Wood soft, weak, compact, brown, 

 weight per cubic foot 26 Ibs. River- or swamp-cotton- 

 wood. Balm-of-gilead. April-May. 



7. Populus grandidentata Michx. Large- 

 toothed Aspen. Fig. 1446. 

 Populus grandidentata Michx. Fl. Bor. Am. 2 : 243. 1803. 



A forest tree with smooth, greenish-gray bark, 

 maximum height about 75, and trunk diameter 2^. 

 Leaves ovate-orbicular, those of very young plants 

 densely wbite-tomentose beneath, sometimes i long, 

 with irregularly denticulate margins, those of older 

 trees tomentose when young, glabrous when mature, 

 short-acuminate, coarsely undulate-dentate, obtuse or 

 truncate at the base, 2 '-4' long; petioles slender, flat- 

 tened laterally; bracts silky, irregularly 4-7-cleft; 

 staminate aments 2'~4' long, about 5" in diameter, 

 drooping; pistillate aments somewhat pubescent, 

 dense, 3-5' long in fruit, also drooping; stigma-lobes 

 narrow ; capsule conic, acute, 2-valved, about 3" long, 

 rather less than l" in diameter, papillose. 



In rich woods, Nova Scotia to Ontario and Minnesota, 

 south to Delaware, North Carolina and Tennessee. Wood 

 soft, weak, light brown, compact; weight per cubic foot 

 29 Ibs. White poplar. April. 



