THE TIMBERS OF COMMERCE 



numerous, 35-50 per sq. mm. : occasional groups of 2-8 pores : 

 " in wide rings a net-work is sometimes discernible " (69). 



Rays. Need lens, fine, size 5 : nearly straight, but avoiding 

 the pores a little : long : denser than the ground-tissue : rather 

 numerous, 6-8 per mm. : rather irregularly spaced, a pore-width 

 or more apart. 



Rings. Fairly clear : boundary, a narrow brown line of 

 Autumn wood, accompanied at times by a thin pore-ring : con- 

 tour coarsely undulating. 



Soft-tissue. " Intermingled with the fibres " (69). Scattered 

 cells. 



Flakes. An important feature : yellowish-brown or brown : 

 numerous towards the centre of the tree, rarer in the older wood. 

 '' Pith. Small, about \ mm. diameter : oblong or three-cornered : 

 brownish. 



Radial Section. Pores fine, inconspicuous scratches : rays 

 need microscope : ring-boundaries rarely perceptible. Flakes 

 long, narrow brown stripes to about 1*5 mm. wide. 



Tangential Section. As the Radial, but the flakes appear as 

 much wider lines to about 3 mm. wide, and the rays are minute, 

 vertical, colourless lines needing considerable magnification. 



Type specimens from trees known before felling. •' 



No. 189. AMERICAN BIRCH. Betula lenta. Linn. 



Plate XIV. Fig. 120. 



Natural Order. Cupuliferse. 



Synonyms. B. carpinifolia, Ehrh. B. excelsa, Hook. B. 

 nigra, Duroi. 



[Note. — The B. lenta, Duroi, is the B. alba, Linn. : that of Regel 

 is B. carpinifolia, Griseb.] 



Alternative Names. Black Birch, Cherry Birch, Mountain 

 Mahogany (49). Mahogany Birch (100). Sweet Birch, Yellow 

 Birch in Prince Edward's Isle : Dwarf Birch in Nova Scotia : 

 River Birch and Mountain Birch in Canada (12). Hainbirke 

 (131). Merisier (65). 



Sources of Supply. Canada and the United States. 



Physical Characters, etc. Recorded dry- weight 37 J-48 lbs. per 

 cu. ft. Hardness Grade 5, compare English Ash, Holly, Elm. 

 Smell and taste none. Solution with water or alcohol colourless. 



Grain. Fine, close and even. Surface smooth and of spark- 

 ling lustre, which is due to the ground and to the shining linings 

 to the pores. 



Bark. " Smooth, reddish-brown when young, scaling later in 

 hard, woody scales " (49). Like that of English Birch. 



Uses, etc. Cabinet-making and for very many other purposes. 



216 



