POPULUS 57 



d. Buds fusiform (widest near 

 the middle, tapering both 

 ways); native tree 4. P. deltoides 



b. Terminal buds mostly less than 

 12 mm, long 



c. Buds short and broad ;native 



swamp tree 9. P. heterophylla 



c. Buds slender, tapering; form 



of tree tall and columnar; 



introduced 5. P. nigra, var. 



italica 



1. _P. tremuloides Michx. Quaking Aspen , A slender tree 

 reaching a height of about 35 m. and a trunk diameter of 1 m. ; 

 bark smooth, light green to white; twigs slender, shiny, reddish- 

 brown; buds conical, brown to black, with 6 or 7 glabrous or cili- 

 ate, somewhat gummy scales; leaf-scars conspicuous, lunate; 

 stipule-scars linear, blackish. Dry or moist woods, Labrador to 

 Alaska, south to West Virginia, Illinois, Iowa, New Mexico, 

 Arizona, and Mexico; the most widely distributed tree in North 

 America (Fig, 29). 



2. P_. grandidentata Michx. Bigtooth Aspen. A tree 10-25 

 m. high, 3-6 dm, in diameter; bark smooth, grayish-green;twigs 

 grayish or yellowish-brown, rather thick, glabrous, dull; buds 

 gray, puberulous, with about 6 or 7 visible scales; flowers in cat- 

 kins, appearing in March, Dry woods and fields, Quebec to Min- 

 nesota, south to North Carolina and Missouri. (Fig. 30), 



3. _P. alba L, White Poplar, A large tree attaining a height 

 of 30 m, and a trunk diameter of 2 m*; bark smooth, light gray;twigs 

 and buds white-tomentose. Introduced from Europe, spreading and 

 naturalized, often too abundant (Fig, 31). 



4. JP. deltoides Marsh. Eastern Cottonwood. A large tree, 

 the greatest of the eastern poplars, sometimes 40 m. tall and with 

 a diameter of 2 m. ; bark rough on old trees, grayish-green; twigs 

 stout, angular, yellowish-brown, glabrous; lenticels large; termi- 

 nal buds glabrous, lustrous brown, resinous, with 6 or 7 visible 

 scales, the lateral buds usually smaller, divergent; leaf-scars 

 large, lunate, elevated; stipule-scars dark, conspicuous. River 

 banks and bottomlands, Quebec to Alberta, south to Florida and 

 Texas (Fig. 32). 



5. P. nigra L , var. italica Muenchh. Lombardy Poplar. 

 Tree to 30 m,high, the branches closely ascending, forming a nar- 



