POPULUS 



55 



POPULUS L. 



Deciduous trees. Bark at first smooth, green, whitish, or 

 orange, becoming gray and fissured on older stems. Twigs 

 moderate, terete or somewhat angled; pith small, 6-angled, con- 

 tinuous or nearly so, brown. Buds moderate, ovoid or elongated, 

 sessile, solitary, with several exposed scales, the lowest placed 

 centrally over the leaf-scar. Leaf-scars alternate, broadly cres- 

 cent-shaped to triangular, somewhat 3-lobed, large; bundle -traces 

 3, or sometimes compound. 



a. Lateral buds with more than 4 ex- 

 posed scales 



b. Twigs and buds shiny or varnished, 



mostly glabrous 

 b. Twigs and buds gray, dull, buds 



silky or tomentose 



c. Twigs glabrous 



c. Twigs hairy or tomentose 



a. Lateral buds with about 4 exposed 

 scales 



b. Terminal buds mostly 12 mm. 

 or more long. 



c. Twigs reddish-brown ;buds 

 quite resinous, very fragrant 

 when crushed 



d. Native tree of Canada and 

 northern United States 



d. Cultivated tree of horticul- 

 tural origin 



c. Twigs yellow to yellowish 

 brown;buds slightly resinous 



1. p. tremuloides 



2. p. grandidentata 



3. P. alba 



6. P. balsamifera 



7. P, gileadensis 



d. Buds widest at the base 

 tapering toward the apex; 

 planted tree 



8. P. eugenei 



