BETULACEJE 



209 



CONSPECTUS OF THE NORTH AMERICAN ARBORESCENT SPECIES. 



Flowers opening- in spring- with or after the leaves ; stamens 4 ; pistillate aments inclosed 

 during- the winter ; nut furnished with a broad wing. 



Leaves ovate, sinuately lobed, lustrous on the lower surface. 



1. A. Sitchensis (B, F, G). 

 Flowers opening- in winter or early spring before the unfolding of the leaves ; pistillate 

 aments usually naked during the winter. 

 Wing of the nut broad. 



Leaves ovate or elliptical, rusty-pubescent on the lower surface ; pistillate aments 

 often inclosed during the winter ; stamens 4. 2. A. Oregoua (B, G). 



Wing of the nut reduced to a narrow border. 



Leaves oblong-ovate, glabrous or puberulous on the lower surface ; stamens 4. 



3. A. tenuifolia (B, F, G). 

 Stamens usually 2 or 3. 

 Leaves ovate or oval, pale and slightly puberulous on the lower surface. 



4. A. rhombifolia (B, F, G). 

 Leaves oblong-lanceolate, acute, pale and sometimes puberulous on the lower sur- 

 face. 5. A. oblongifolia (H). 

 Flowers opening in autumn from aments of the year ; stamens 4 ; wing of the nut reduced 

 to a narrow border. 



Leaves oblong-ovate or obovate, dark green and lustrous above, pale yellow-green 

 below. 6. A. maritima (A). 



1. Flowers opening in spring with or after the leaves : pistillate aments inclosed during 

 the winter. 



1. Alnus Sitchensis, Sarg. Alder. 



Leaves ovate, acute, full and rounded and often unsymmetrical and somewhat 

 oblique, or abruptly narrowed and cuneate at the base, divided into numerous short 

 acute lateral lobes, sharply and doubly serrate, with straight glandular teeth, glandu- 



lar-viscid as they unfold, at maturity membranaceous, yellow-green on the upper 

 surface, pale and very lustrous on the lower surface, glabrous, or villous along the 

 under side of the stout midribs, with short brown hairs also forming tufts in the axils 

 of the numerous slender primary veins, 3'-6' long, l^'-4' wide ; their petioles stout, 



