184 BETULACEAE 
Pistillate catkins erect or spreading, scales each covering 3 flowers in 
the axis. 
Trees. 
Bark white or yellowish-white. 
Leaves deltoid. 
Green ot eu Sg sp een Te es, Sow ea ten a Bn Sento 
Bluish-green. >... <2. net Sena fol We Ws on we ete B. coerulea 
heaves” egg-shaped “<) 7 S)emmeinaem oo =) eee ‘B. papyrifera 
Bark brown or greenish-brown. 
Pistillate catkin with a stem . . Sree ce i IE er; 
Pistillate catkin stemless or nearly sO. 
Bark dark brown . . é - » « Bs dents 
Bark yellowish or greenish- brown. 
‘Twigs not! «silky va ueciee eS ae Se ees B. lutea 
Twigs (dite wm Silkyeus: cremmie) ce fo. Seneetien alleghaniensis 
Shrubs. 
Young branchlets dotted with wart-like plands - « « «© « SB. glandulosa 
Young branchlets not glandular ses © « » Bug 
1. B. populifolia, Marsh. (Fig. 2, pl. 27.) American WHITE 
Bircu. Tree, from 15 to 30 ft. high. Bark smooth and white. Twigs 
brown. Leaves triangular with the free point very slender. Smooth and 
shining both sides, tremulous. Mostly in damp places but grows in dry 
soil, most of our area. 
2. B. coerulea, Blanchard. Buiue Bircw. Larger than No. 1. 
Foliage bluish-green; young shoots warty. Leaves egg-shaped to del- 
toid on long leaf-stalks, irregularly and sharply toothed; base of leaf 
nearly straight across, apex tapering to a long narrow point, both sur- 
faces smooth. Woods, Vermont. May. 
3. B. papyrifera, Marsh. Paper or Canoe Bircnw. Tree, 50 to 65 
ft. high; bark white, splitting into layers. Leaves egg-shaped to heart- 
shaped, free point less tapering than in No. 1, pale above, somewhat 
dotted below, double serrations with petiole about 1/3 length of leaf. 
Rich woods and wet places, throughout our range. 
4., B. nigra, L. (Fig. 3, pl. 27.) River Biron. Rep Bircu. Tree, 
50 to 75 ft. high; bark greenish-brown, peeling in very thin layers. 
Leaves rhombie ovate, tapering at each end, serrations irregular, the 
larger serrations including several of the smaller, smooth and deep green 
above, light below. Banks of streams and lakes, east Mass., southward. 
5. B. lenta, L. (Fig. 1, pl. 27.) CHEerRy Biron. Sweet Brrca. 
Biack Biren. Tree 50 to 70 ft. high; bark dark brown, not separating 
into layers like No. 3. Twigs very aromatic. Leaves egg-shaped, some- 
times heart-shaped; doubly serrate, serrations generally regular, bright 
green above, veins beneath dull green. Rich woods, our range. 
6. B. lutea, Michx. YeLrow Bircu. Gray Biren. Tallest of the 
birches. Bark yellowish or gray; not always separable into layers; 
twigs less aromatic than No. 4; leaves ovate or long-ovate, generally 
with tapering points, dull green above, downy on the veins beneath. 
Rich moist woods, our range. 
7. B. alleghaniensis, Britton. SournerN YerLLow Bircn. Resem- 
bles B. lutea. Young twigs downy with long hairs. Leaves egg-shaped, 
tapering, 5 in. long, coarsely and sharply toothed, heart- shaped at base 
or rounded, dark green above, yellow-green and more or less downy be- 
neath, especially on the veins. Leaf-stalks downy 4 in. long. Stamen 
bearing catkins about 24 in. long. Mass., northward, 
