256 ANATOMY OF THE GYMNOSPERMS 



squarish, uniform, in very regular rows. Resin cells none. Resin- 

 bearing tracheids few, rather prominent, scattering through the sum- 

 mer wood, more rarely in the spring wood. Medullary rays somewhat 

 resinous and prominent, i cell wide, distant 2-15 rows of tracheids. 



Radial. Medullary rays sparingly resinous throughout, wholly devoid of 

 tracheids. Ray cells straight, or in the summer wood contracted at 

 the ends, equal to 7-8 spring tracheids ; the upper and lower walls 

 medium, unequal, somewhat distantly and imperfectly pitted in the 

 spring wood, but strongly pitted in the summer wood ; the terminal 

 walls strongly pitted ; the lateral walls with small pits which become 

 conspicuously bordered in the summer wood where the orifice is 

 reduced to a slit and the pit is round, 1-2, chiefly 2, or in the marginal 

 cells 2-4, per tracheid. Resin-bearing tracheids not numerous, the 

 resin sometimes massive in the summer wood, but forming a periph- 

 eral layer in the spring wood. Bordered pits elliptical, in i row or 

 sometimes in pairs. Pits on the tangential walls of the summer 

 tracheids somewhat numerous but small and flat. 



Tangential. Rays small to medium, the cells narrow, rather uniform, oval 

 to oblong. 



A tree 18-24 m. high and upwards of .60 m. in diameter. 

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



Relative specific gravity 0.3565 



Percentage of ash residue 0.54 



Approximate relative fuel value 35-46 



Coefficient of elasticity in kilograms on millimeters . . . 972. 



Ultimate transverse strength in kilograms 273. 



Ultimate resistance to longitudinal crushing in kilograms . 5557. 



Resistance to indentation to 1.27 mm. in kilograms . . 1048. 

 (Sargent) 



High mountains of North Carolina and Tennessee, forming somewhat 

 extensive forests on moist slopes between 5000 and 6500 feet (Sargent). 



2. A. lasiocarpa, Nutt. 



Mountain Balsam. Balsam Fir 



Transverse. Growth rings narrow, uniform, the structure open throughout. 

 Summer wood very thin, rarely upwards of 14 tracheids, the transition 

 to the spring wood gradual. Spring wood of large, squarish tracheids 

 with rather thin walls, uniform in regular rows. Resin cells and resin- 

 ous tracheids wholly wanting. Medullary rays not prominent, barely 

 if at all resinous, i cell wide, distant 2-8, more rarely 15, tracheids. 



Radial. Rays very sparingly resinous, wholly devoid of tracheids. Ray 

 cells more or less conspicuously contracted at the ends, equal to about 

 7 spring tracheids ; the upper and lower walls thick, unequal, and 

 strongly pitted throughout ; the terminal walls thin, often devoid of 

 pits ; the lateral walls with obscurely bordered pits, the large orifice 

 lenticular, variable, 1-4, or in the marginal cells rarely 5, per tracheid, 

 and distinctly bordered, in the summer wood reduced to i per tracheid 



