BETULA 71 



scales tomentose; nut broadly ovate, winged, pubescent. Bottom- 

 lands, Florida to Texas, north to New Hampshire, Michigan, 

 Minnesota, and Kansas (Fig. 55). 



4. B. populifolia Marsh. Gray Birch . Bushy tree up to 20 m. 

 high; bark close, not exfoliating, chalky -white with dark elongate 

 markings; twigs slender, glabrous, wiry, often resinous -warty; 

 buds ovoid, glabrous, about 6 mm. long; fruiting catkins 1.8 cm. 

 long. Sterile soil. Prince Edward Island to Quebec, south to Dela- 

 ware and Indiana (Fig. 56). 



5. B. papyrifera Marsh. Paper Birch . Canoe Birch . A tree 

 up to 25 m. high, with a trunk diameter of 1 m. ;bark lustrous, 

 white or bronze, peeling in thin layers; buds glabrous; fruiting 

 catkins 1. 5-4. 5 cm. long, spreading or drooping on slender ped- 

 uncles, the scales cili ate -margined. Woods, Labrador to Alaska, 

 south in the Appalachians to West Virginia and North Carolina, in 

 the western mountains to Montana and Washington (Fig. 57 ), 



ALNUS B. Ehrh. (Betulaceae) 



Deciduous shrubs with gray bark. Twigs somewhat 3-sided; 

 pith small, 3-sided, continuous. Buds sessile or stalked, rather 

 large, solitary, with 3 scales. Leaf-scars alternate, half-round, 

 raised; bundle-traces 3 or compound. Both kinds of flowers in 

 catkins, the staminate for next season usually conspicuous in win- 

 ter, along with the persistent cone-like fruiting catkins of the pre- 

 ceding season and the small undeveloped pistillate catkins of the 

 next season. 



a. Buds sessile, with 3-6 imbricated 



scales 1. A. crispa 



a. Buds stalked, with 2 or 3 scales 



b. Stems with linear transverse 



lenticels; fruiting catkins bent 



downwards 2. A. rugosa 



b. Lenticels shorter, fewer, darker; 



fruiting catkins erect 3. A. serrulata 



1. _A. crispa (Ait. ) Pursh. Green Alder . Ascending and bushy 

 shrub up to 3 m. high; young branches glabrous or sparsely pubes- 

 cent; buds sessile. Labrador to Alaska, south to North Carolina, 

 Michigan, Minnesota, and Alberta (Fig. 58). 



2. _A. rugosa (DuRoi) Spreng. Speckled Alder . Hoary Alder . 

 (A. incana of authors, not (L. ) Moench. ). A shrub or small tree 

 2-8 m. high, the twigs glabrous in winter; trunk marked with 



