LIBOCEDRUS 219 



and sparingly pitted ; the terminal walls straight or diagonal, some- 

 times curved, entire ; the lateral walls with oval or rounded pits, about 

 2-3 per tracheid in radial series. Bordered pits numerous, but becom- 

 ing 2-rowed toward the summer wood, though distinctly crowded into 

 2-3 compact rows in the earlier spring tracheids. Resin cells not 

 conspicuous. 



Tangential. Resin cells conspicuous but not numerous, about 3 times 

 longer than broad. Medullary rays rather numerous and narrow, 

 often very high, strictly i-seriate ; the cells oval, more rarely round 

 in the low rays. 



Material silicified. 



A distinctive species occurring in the Laramie (Eocene) at Cochrane, 

 Alberta. 



7. LIBOCEDRUS, ENDL. PLATES 32 AND 33 



Transverse. The thin and rather dense summer wood usually showing a 



more dense median layer. Resin passages wholly wanting. Resin 



cells numerous and conspicuously zonate. 

 Radial. Rays wholly without tracheids. The terminal walls of the ray 



cells straight or curved, entire, locally thickened or even coarsely 



pitted. Tracheids wholly without spirals. 

 Tangential. Fusiform rays wholly wanting, the rays strictly of one kind. 



1. L. decurrens, Torn 



White Cedar. Bastard Cedar. Post Cedar. Incense Cedar 



Transverse. Growth rings broad. The dense summer wood rather thin 

 and composed of 8-14 tracheids, often more or less double ; the tran- 

 sition from the spring wood gradual. Spring tracheids in regular 

 rows, uniform, squarish, large and thin-walled, the structure open. 

 Resin cells numerous, prominent, large, in a very broad band or 

 scattering through the late spring wood. Medullary rays prominent, 

 numerous, resinous, i cell wide; distant 2-8, rarely 15, rows of 

 tracheids. 



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

 equal to about 4-8 spring tracheids ; the upper and lower walls medium 

 and entire, or again distantly and often imperfectly pitted ; the ter- 

 minal walls thin, straight, or curved and locally thickened or even 

 coarsely pitted ; the lateral walls with small, narrowly bordered, oval 

 pits with a lenticular, diagonal orifice, 1-4 per tracheid. Bordered 

 pits in i row, sometimes in pairs, numerous. Pits on the tangential 

 walls of the summer tracheids numerous and large, extending almost 

 through the entire zone. Resin cells 20-30 p. wide, chiefly 175-225 p. 

 long, less commonly upwards of 475 p.. 



Tangential. Rays very variable, often 2-3 seriate at the center or near 

 one end, sparingly resinous, rather broad ; the cells round or oval, 

 uniform, the walls medium. 



