102 American Midland Naturalist Monograph No. 2 



5. Leaves ovate-lanceolate, glabrous; river banks and wet ground, n.e. III. 



[P. balsamifera sensu auth., non L.] Balsam Poplar 



P. tacamahaca Mill. 



5. Leaves ovate, cordate; petioles, and veins on the lower surface of the 

 blades puberulent or pubescent; planted and sometimes persisting; 

 origin unknown. Athens, Menard Co., E. Hall in 1861; Waukegan, 

 Gates 2780; Pecria, Brendel. Balm of Gilead P. candicans Ait. 



1 . Petioles strongly flattened laterally, at least near the blade. 

 6. Buds pubescent or glabrous, not glutinous; catkin-scales with silky hairs; 

 stigmas linear; leaves dull or gray-green. 



7. Leaves coarsely dentate, the blades 6-10 cm. long, white-tomentose be- 

 neath when young, glabrate in age, broadly ovate, the base truncate 

 to broadly cuneate; bud-scales finely appressed-pubescent, glabrate; 



river banks. Apr.-May. Large-toothed Aspen 



P. grandidentata Michx. 



7. Leaves finely crenate, glabrous from the beginning, ovate to orbicular, 



the blades 3-6 cm. long; buds glabrous (or merely ciliolate), glossy; 

 thickets and margins of woods in the centr. and n. parts of the state. 

 Apr. Quaking Aspen P. tremii'oidcs Michx. 



6. Buds viscid, glossy, glabrous; catkin-scales glabrous; stigmas broad; leaves 

 bright or yellow green. 



8. Leaves rhombic-ovate, cuneate at base, crenate-serrate; petioles gland- 



less; branches closely ascending or nearly erct, forming a narrow 

 tree; native of Eur.; cult, and sometimes found wild. Lombardy 

 Poplar P. italica Moench 



8. Leaves broadly deltoid, mostly truncate at base, coarsely dentate with 

 incurved teeth; petioles usually with a pair of glands at the base of 

 the blade; branches widely spreading, forming a broad-crowned tree; 

 along streams and in low ground, common. Mar. -Apr. [P. balsami- 

 fera L.; P. vtrginiana Foug.; P. mondijera Ait.} Cottonwood 



P. dcltoides Marsh. 



2. Salix L.— Willow 



1. Scales of the catkins pale or yellowish, caducous; catkins on short leafy 

 lateral branchlets. 

 2. Style not more than 0.5 mm. long. 



3. Ovaries and capsules distinctly pedicelled. 



4. Ovaries and capsules glabrous; leaves lanceolate, petioled, finely 

 serrate; stamens 3-9. 

 5. Capsules 3-6 mm. long at maturity; trees 10-20 m. tall. 



6. Capsules 3 mm. long; leaves linear-lanceolate, green on both 

 sides, the petioles 3-6 mm. long; common along streams. May. 

 Black Willow S. nigra Marsh. 



6. Capsules 4-5 mm. long; leaves lanceolate, glaucous beneath, the 

 petioles usually 5-15 mm. long; along streams. Apr.-May. 

 Peach-leaved Willow S. amygdaloidcs Anders. 



