14 BULLETIN 1050, U. S. DEPAETMENT OF AGRICULTURE. 



BIRCH. 



Sweet birch (Bettila lenta Linn.) ; yellow birch (Betula lutea Michx. f.). 

 BiECH Family ( Betulace^ ) . 



OTHEE NAMES. 



Sweet birch is also known as cherry birch, black birch, and ma- 

 hogany birch. 



Yellow birch is also known as gray birch, silver birch, and swamp 

 birch. 



The heartwood of both species is usually sold as " red birch " and 

 the sapwood as " yellow birch." 



Other species of birch are rarely cut into lumber. 



WHERE GROWN. 



Sweet birch grows within an area that extends from Newfoundland 

 to eastern Iowa, and south to northern Florida. It is of commer- 

 cial importance, principally in the East, from New York State south 

 along the Appalachian Mountains, although it is cut as far west as 

 Wisconsin. 



Yellow birch occurs from Newfoundland to northern Minnesota, 

 and through the northern States to eastern Tennessee, North Caro- 

 lina, and Delaware. It is most abundant and reaches its largest size 

 in northern New England and New York and in northern Michigan 

 and Wisconsin. 



PHYSICAL PROPERTIES. 



Although sweet birch averages slightly heavier and harder than 

 yellow birch, the difference is so little that usually no distinction is 

 made between the two species when, used in the form of lumber. 

 Both species are hard, heavy, and strong in bending. 



Birch has somewhat of a tendency to warp, but not so much as 

 red gum and other species with decidedly interlocked grain. 



The heartwood is reddish brown; the sapwood, which is often 

 wide, is practically white. Much sapwood is used in the manufac- 

 ture of furniture with a mahogany finish. It is difficult to hide its 

 identity since any wear or fracture is likely to disclose the white 

 wood underneath the finish. 



STRUCTURE. 



The pores in birch are of such size that they can barely be seen 

 in good light without a lens on the smoothly cut end surface. On 

 the longitudinal dressed surface they appear as very fine grooves. 

 They are almjost uniform in size throughout each annual ring, 

 although o(;casionally they are noticeably smaller toward the end of 

 each year's growth. (See fig. 9.) The annual rings are defined by 

 fine lines. 



