218 ANATOMY OF THE GYMNOSPERMS 



wood somewhat gradual. Spring wood very open ; the tracheids 

 very large, thin-walled, hexagonal, rather uniform. Resin cells numer- 

 ous, large, not strongly resinous, distinctly zonate or sometimes scat- 

 tering throughout the growth ring. Medullary rays prominent but 

 sparingly resinous, distant 2-8 or more rarely 13 rows of tracheids, 

 I cell wide. 



Radial. Ray cells sparingly resinous, usually more or less contracted at 

 the ends, equal to 3-5 spring tracheids ; the upper and lower walls 

 thickish, rather unequal and entire or distantly and often imperfectly 

 pitted ; the terminal walls thin, sometimes obscure, often curved, not 

 pitted or locally thickened ; the lateral walls with prominent and con- 

 spicuously bordered pits, round, 1-4, or more rarely 7, per tracheid, 

 the very narrow, lenticular orifice often as long as the outer limits 

 of the pit. Bordered pits chiefly elliptical, numerous, variable, often 

 paired and in the earlier spring wood becoming imperfectly 2-seriate. 

 Pits on the tangential walls of the summer tracheids very numerous, 

 not very large. Resin cells sparingly resinous, 25 p, wide, chiefly 

 140 n. long, but ranging upwards of 310 /x. 



Tangential. Rays numerous, medium to high, very sparingly resinous ; the 

 round or oval cells rather broad and thick-walled, rarely in pairs. 



Wood very durable in the soil and of great economic value. 



Relative specific gravity -4543 



Approximate fuel value 45- 2 4 



Coefficient of elasticity in kilograms on millimeters . . . 1032. 



Ultimate transverse strength in kilograms 291. 



Ultimate resistance to longitudinal crushing in kilograms . 6771. 



Resistance to indentation to 1.27 mm. in kilograms . . 1166. 

 (Sargent) 



Material silicified. 



Delaware to Florida and westward through the Gulf States to Texas; north- 

 ward through Tennessee, Kentucky, and southern Missouri to southern 

 Illinois and Indiana (Sargent). 



This well-known Tertiary plant, chiefly represented by its foliage and fruit, 

 is known through its woody structure in only one instance, occurring in 

 the Eocene of the Porcupine Creek and Great Valley groups. 



2. * * T. laramianum, Penh. 



Transverse. Growth rings prominent, rather broad. Summer wood promi- 

 nent, upwards of 17 tracheids thick and passing somewhat gradually 

 into the broad spring wood. Spring tracheids large, squarish-hex- 

 agonal, thin-walled, uniform in regular rows. Resin cells obscure and 

 forming an open zone on the inner face of the summer wood. Resin 

 passages wholly wanting. Medullary rays numerous, narrow, distant 

 about 2-8 rows of tracheids. 



Radial. Medullary rays wholly devoid of tracheids. Ray cells straight, 

 equal to about 3 tracheids ; the upper and lower walls rather thick 



