30 BULLETIJSr 12, U. S. DEPAKTMENT OF AGEICULTUEE. 



MOUNTAIN BIRCH. 



(Betula fontinaUs.) 



Mountain birch is small, and no use other than local has been 

 reported for it, nor dees it promise to become important in the future. 

 It is a mountain species, as its name implies. It is found in locali- 

 ties from British Columbia to Colorado, and thence westward to the 

 Sierra Nevada Mountains of central California. 



RIVER BIRCH. 



{Betula nigra.) 



PHYSICAL PROPERTIES. 



Weight of dry irood. — .35.91 poiuids per cubic foot (Sargent). 



Specific gra vitij. — 0.5762 ( Sargent ) . 



Ash. — 0.35 per cent weight of dry wood (Sargent). 



Fuel "value. — 76 per cent tliat of white oak (Sargent). 



Breaking strength (modulus of rupture). — 13.622 pounds per square inch, or 

 109 per cent that of white oak (Sargent). 



Factor of stiffness (modulus of elasticity). — 1.560.000 pounds ]^er square inch, 

 or 118 per cent that of white oak (Sargent). 



Wood light, rather hard, strong, compact ; medullary rays numerous, obscure ; 

 color brown, the sapwood much lighter. 



Height, 50 to 80 feet : diameter. 18 to 30 inches. The species reaches its 

 largest size in the far South, particularly in western Florida, Louisiana, and 

 Texas. 



SUPPLY. 



No estimate of the quantity of river birch has been made. The 

 species nowhere forms forests, but is found scattered along banks 

 of rivers, margins of ponds, and in swamps where the land is above 

 water most of the year. The tree will, however, do well on ground 

 subject to rather long periods of overflow. Its range extends from 

 Massachusetts to Florida, and Avestwarcl to Texas, eastern Kansas, 

 Iowa, and Minnesota. This area exceeds a million square miles, but 

 the actual quantity of the timber can not be judged by the extreme 

 outposts of its range, because over large districts it is not found 

 and in others it is very limited. Among the names by which it is 

 known in different regions are reel birch, water birch, blue birch, and 

 black birch. 



Eiver birch is one of the few American trees which ripen their 

 seeds in the spring or early summer. The habit of this tree in grow- 

 ing along watercourses and passing uninjured through long periods 

 of inundation suggests that water has much to do in the dispersal of 

 the seeds. The tree, nevertheless, often grows entirely above the 

 highest flood line. It is like the sycamore, in that the situation in 

 Avhich it thrives best is seldom suited to agriculture, because too wet 

 or too liable to frequent overfloAv. It is, therefore, a waste-land tree, 



