54 FOUNDATIONS OF BOTANY 
and truncate base, unevenly twice serrate, with rather long, slender 
petioles, which allow the leaves to quiver like those of the aspen. 
Bark scaling off in white strips and layers, but not in nearly as 
large sheets as that of the rarer canoe birch (B. papyrifera). The 
commonest birch of New England. 
4. B. alba, L. European Wuite Bircn, Cut-LEAVED BIRCH. 
A tree 50 to 60 ft. high, often with drooping branches. Leaves 
triangular-ovate, truncate, rounded or somewhat heart-shaped at 
the base, not strongly taper-pointed except in the cut-leaved form. 
Commonly cultivated from Europe. Resembles No. 3, but has 
whiter bark and (the weeping form) much more slender branches. 
Vv. ALNUS, Tourn. 
Shrubs or small trees. Leaves petioled, serrate. Flower- 
buds stalked, appearing the previous season; staminate cat- 
kins racemed, drooping, flowers 3-6 in the axil of each bract, 
subtended by 1-2 bractlets, perianth 4-parted, stamens 4, fila- 
SF” Se 
id AN 
Oy: b 
SiR 
Shu Lf 
S874) ak 
a Wyss 
we 5 
Se sa 
SUS oe s 
Wis way 
ws S me 
eae 
PAU om > 
Seg Thee 
nc 5 
Ba | yaad Cc 
(any PONS 
ft : 4 ) 
sy 
A win 
Sih 
ern 
AR 
Peay 
Ww 
Fic. 8.— Alnus glutinosa. 
A, a flowering twig; s, staminate catkins ; p, pistillate catkins; B, a group of 
staminate flowers, enlarged; C, two pistillate flowers, enlarged. 
