258 ANATOMY OF THE GYMNOSPERMS 



summer wood becoming very much shorter ; the upper and lower walls 

 medium, unequal, the narrow pits not very numerous, except in the 

 summer wood, often imperfectly formed ; the terminal walls closely 

 pitted, becoming more prominent in the summer wood ; the lateral 

 walls with narrowly bordered oval pits, 1-2, or in the marginal cells 

 upwards of 4, per tracheid, the orifice broadly lenticular or oval. Bor- 

 dered pits round or elliptical, numerous in i row, variable, but chiefly 

 two thirds the diameter of the tracheid, the large orifice round. Pits on 

 the tangential walls of the summer tracheids few, small, rather open. 

 Resin cells and resinous tracheids wholly wanting. 



Tangential. Rays not very numerous, medium to high, somewhat resinous, 

 strictly i -seriate ; the cells somewhat unequal and variable, chiefly 

 round or oval, sometimes oblong. 



4. * A. balsamea, Mill. 

 Balsam Fir. Balm-of-Gilead Fir. Canada Balsam Fir 



Transverse. Growth rings thick. Summer wood thin, open, passing very 

 gradually into the spring wood. Spring wood very open, the large 

 tracheids squarish-hexagonal, thin-walled, uniform in regular rows. 

 Resin cells wanting. Medullary rays not numerous or prominent, 

 i cell wide, distant 2-8, rarely 12, rows of tracheids. 



Radial. Ray tracheids few, narrow, and very unequal ; the rays barely 

 resinous. Ray cells conspicuously contracted at the ends and equal 

 to 2-6 spring tracheids ; the upper and lower walls medium, unequal, 

 somewhat distantly and finely, but often imperfectly, pitted ; the ter- 

 minal walls coarsely pitted, especially in the summer wood ; the lateral 

 walls with small, round or oval pits, 2-4, more rarely upwards of 8, per 

 tracheid. Bordered pits elliptical, large, one half the diameter of the 

 tracheid, chiefly rather scattering, in i row or often in pairs, and 

 more or less imperfectly 2-rowed. Pits on the tangential walls of the 

 summer wood not numerous, chiefly quite small. 



Tangential. Rays medium, the cells narrow, uniform, oval to oblong. 



A tree 21-27 m. high, with a trunk upwards of .60 m. in diameter. 

 Wood very light, soft, not strong, coarse grained, compact, not durable. 



Relative specific gravity 0.3819 



Percentage of ash residue 0.45 



Approximate relative fuel value 38.02 



Coefficient of elasticity in kilograms on millimeters . . 819. 



Ultimate transverse strength in kilograms 220. 



Ultimate resistance to longitudinal crushing in kilograms 5851. 



Resistance to indentation to 1.27 mm. in kilograms . . 1202. 

 (Sargent) 



Abundant in swamps throughout the eastern provinces of Canada, north- 

 ward to James Bay and westward to the Athabasca River in latitude 58 

 (Macoun) ; southward through the northern United States to Pennsyl- 

 vania, and along the Allegheny Mountains to the high peaks of Virginia ; 



