218 



TREES OF NORTH AMERICA 



growing sparingly near the banks of streams in forests of coniferous trees and in large 

 numbers on sunny slopes and hillsides; the common Birch-tree of the Yukon basin. 



X Betula commixta Sarg., a shrub, growing on the tundra near Dawson, Yukon Terri- 

 tory, is believed to be a hybrid between B. alaskana and B. glandulosa Michx. 



8. Betula fontinalis Sarg. Black Birch. 



Leaves ovate, acute or acuminate, sharply and often doubly serrate, except at the 

 rounded or abruptly cuneate often unequal base, and sometimes slightly laciniately 

 lobed, pale green, pilose above, and covered by conspicuous resinous glands when they 

 unfold, at maturity thin and firm, dark dull green above, pale yellow-green, rather lus- 

 trous and covered by minute glandular dots below, l'-2' long, f'-l' wide, with a slender 

 pale midrib, remote glandular veins, and rather conspicuous reticulate veinlets; turning 

 dull yellow in the autumn; petioles stout, puberulous, light yellow, glandular-dotted, 

 flattened on the upper side, often flushed with red, $'-' long; stipules broadly ovate, 

 acute or rounded at apex, slightly ciliate, bright green, soon becoming pale and scarious. 

 Flowers: staminate aments clustered, |'-f long and y 1 ^' thick during the winter, with 

 ovate acute light chestnut-brown scales pale and slightly ciliate on the margins, becoming 

 2'-2i' long, and about f thick, with apiculate scales; pistillate aments short-stalked, 

 about f long, with ovate acute green scales; styles bright red. Fruit: strobiles cylindric, 

 rather obtuse, puberulous or nearly glabrous, l'-l|' long, \' thick, erect or pendulous on 



Fig. 206 



slender glandular peduncles, J' to nearly f in length; their scales ciliate, puberulous, 

 the lateral lobes ascending, shorter than the middle lobe; nut ovoid or obovoid, puberulous 

 at apex, nearly as wide as its wing. 



A tree 20-25 high with a short trunk, rarely more than 12' or 14' in diameter, ascending 

 spreading and somewhat pendulous branches forming a broad open head, and slender 

 branchlets, when they first appear light green glabrous or puberulous and covered with 

 lustrous resinous glands persistent during their second season, and dark red-brown in their 

 first winter; more commonly shrubby, with many thin spreading stems forming open clus- 

 ters, 15-20 high; often much lower, and frequently , crowded in almost impenetrable 

 thickets. Winter-buds ovoid, acute, very resinous, chestnut-brown, \' long. Bark about 

 thick, dark bronze color, very lustrous, marked by pale brown longitudinal lenticels 

 becoming on old trunks often 6'-8' long and \' wide. Wood soft and strong, light brown, 

 with thick lighter-colored sapwood; sometimes used for fuel and fencing. 



Distribution. Moist soil near the banks of streams usually in mountain canons; gen- 



