BIRCH ALDER 345 



flowers in short, mostly erect catkins which become cones at maturity, 2 or 3 

 naked flowers being borne under each 3-lobed bract: fruit winged and seed- 

 like: leaves simple, toothed or serrate; bark often aromatic. 



a. Brawn-barked birches: leaves ovate. 



B. lenta, Linn. Cherry birch. Sweet birch. Tall tree, the bark tight 

 (not peeling in layers), the twigs very aromatic: leaves oblong-ovate, some- 

 what cordate at base, doubly serrate, becoming glossy above: bracts of the 

 oblong-cylindric fruiting catkins with wide-spreading lobes. Rich woods. 



B. lutea, Michx. YeUow or gray birch. Bark grayer or silvery, peel- 

 ing in layers: leaves scarcely cordate, dull, more downy: bracts of the 

 short-oblong fruiting catkins with scarcely spreading scales: tree less aro- 

 matic than the other. Same range. 



aa. White-barked birches: leaves triangular or broad-ovate. 



B. papyrifera, Marsh. Paper birch. Canoe birch. Tree of medium 

 to rather large size, with the bark peeling in very large plates or layers: 

 leaves broad-ovate and often somewhat cordate, dull green. Pennsylvania, 

 north. , 



B. populifolia, Ait. American white birch. Small and slender tree with 

 rather tight, glistening, white bark: leaves triangular-acuminate, toothed, 

 dangling, and moving incessantly in the wind. Northeastern states. 



B. alba, Linn. European white birch. A larger tree, with triangular- 

 ovate leaves which are pointed but not long-acuminate. Europe. The com- 

 mon cultivated white birch. There are weeping forms (Fig. 6). 



5. ALNUS. ALDER. 



Much like Betula, but smaller trees or bushes: flowers with a 3-5- 

 parted calyx, and the small, short, fertile catkins composed of thickened, 

 woody scales. In the following, the flowers appear before the leaves in 

 earliest spring, from catkins formed the previous year and remaining partly 

 developed during winter. Common along streams. 



A. incana, Moench. Speckled alder. Shrub or small tree, with pubescent 

 branches: leaves oval to oblong-ovate, acute, doubly serrate, glaucous and 

 downy underneath: cones about ^ in. long, mostly sessile. 



A. rugdsa, Spreng. (A. serrulata, Willd.). Smooth alder. Leaves elliptic 

 or obovate, acute or rounded at the apex, finely serrate, the under side 

 of the leaves smooth or pubescent only on the veins: cones short-stalked. 



A. vulgaris, Hill. Black alder. Leaves orbicular or very broadly obo- 

 vate, not acute, irregularly serrate, dull and nearly smooth beneath: cones 

 peduncled. Europe. Planted, some varieties with divided leaves. 



X. URTICACE^E. NETTLE FAMILY. 



Trees and herbs, with small apetalous flowers in small clusters or 

 solitary: leaves mostly straight-veined, with stipules: plants dioecious 

 or monoecious, or flowers perfect in the elms: stamens usually as many 



