276 ANATOMY OF THE GYMNOSPERMS 



3. * * P. miocena, Penh. 



Transverse. Growth rings broad and prominent ; the tracheids of the spring 

 wood large and thin-walled, the structure passing gradually into the 

 thin but rather prominent summer wood composed of about 3-10 rows 

 of thick-walled tracheids. Resin cells not obvious. Resin passages 

 small, not very numerous, chiefly in the summer wood, often double, as 

 in P. Douglasii ; the epithelium cells small and thick-walled. Medul- 

 lary rays slightly resinous. The entire structure of the transverse 

 section bears a strong resemblance to the fine-grained wood of P. 

 Douglasii. 



Radial. Bordered pits in i row. Cells of the medullary rays straight, the 

 thin upper and lower walls devoid of pits. Pits on the lateral walls of 

 the ray cells about 4 per tracheid. 



Tangential. Ordinary rays i-seriate or 2-seriate in part, the cells oval or 

 round, thick-walled, about 24.5 p. broad. Fusiform rays narrow, the 

 cells thick-walled, the resin canal narrow. 



Material silicified or preserved in the natural state. 



Eocene of the Great Valley and Porcupine Creek groups, Saskatche- 

 wan ; Miocene of Cariboo, British Columbia. 



15. * LARIX, TOURN. PLATES 48 AND 49 



Transverse. Summer wood prominent, usually dense, the transition from 

 the spring wood more or less abrupt. Resin passages without thy- 

 loses but with thick-walled epithelium. Resin cells somewhat frequent, 

 but scattering on the outer face of the summer wood. 



Radial. Ray tracheids prominent, sometimes interspersed ; the terminal 

 walls of the parenchyma ray cells thick and strongly pitted. Bor- 

 dered pits in i or 2 rows. Tracheids wholly without spirals. 



Tangential. Fusiform rays prominent, usually high and narrow, the cells 

 small and thick-walled, the resin passage usually small. Cells of the 

 ordinary rays oval to oblong. 



A well-defined genus, at once distinguished by the narrow and usually high 

 fusiform rays, the resin cells scattering on the outer face of the summer 

 wood, and the absence of spiral tracheids. 



SYNOPSIS OF SPECIES 



Bordered pits in 1-2 rows. 



Pits on the tangential walls of the summer wood not confined to the 

 outermost tracheids. 



Pits on the lateral walls of the ray cells 2-6 or 8 per tracheid. 

 Ray cells (tangential) rather unequal, sometimes in pairs, 

 somewhat variable, oval or oblong, 

 i. L. occidentalis. 



