168 



TREES OF THE NORTHERN UNITED STATES 



C. Leaves roundish heart-shaped ; bark on trunk greenish- 

 white 2. 



C. Leaves large, ovate, with large, irregular, sinuate 

 teeth 3. 



B. Buds covered with aromatic, glutinous resin. (D.) 



D. Tree tall, spire-shaped 5. 



D. Not very spire-shaped ; young twigs sharply angled or 



winged, leaves 6 to 10 in. long, broadly deltoid, serrate 



with incurved teeth 6. 



D. Not spire-shaped ; young twigs not angular 7. 



A. Leafstalk not decidedly flattened; leaf-margin crenate. (E.) 

 E. Buds not glutinous ; leaves white-woolly beneath when 



young 4. 



E. Buds very glutinous ; leaves large, shining green on both 

 sides ...8. 



1. P6pulus &lba, L. (WHITE POPLAR OK 

 ABELE TREE.) Leaves roundish, slightly 

 heart-shaped, wavy toothed or lobed, soon 

 green above, very white-cottony beneath 

 even when old ; buds without the sticky 

 coating common in the genus. Branches 

 very white with down when young. Boot 

 creeping and producing numerous suckers. 

 A large tree, 50 to 80 ft. high, of rapid growth, 

 often cultivated ; from Europe. Leaves and 

 branches very variable, forming several 

 named varieties in the catalogues of the nurseries. 



2. P6pulustremuloldes,Michx. (QUAK- 

 ING-ASP. AMERICAN ASPEN.) Leaves round- 

 ish heart-shaped, with a short sharp point, 

 and small, quite regular teeth ; downy when 

 young, but soon smooth qn both sides; 

 margins downy. Leafstalk long, slender, 

 compressed, causing the leaves to tremble continually in the slight- 

 est breeze. Leaf with 2 glands at the base on the upper surface ; buds 

 varnished. A medium-sized tree, 30 to GO ft. high; bark greenish- 

 white outside, yellow within, quite brittle. Common both in forests 

 and in cultivation. 



P. tremuloldes. 



3. Pdpulus grandidentata, Michx. (LARGE-TOOTHED ASPEN.) 

 Leaves large, 3 to 5 in. long, roundish-ovate, with large, irregular, sinu- 



