PINUS 291 



the walls rather thin, but the structure as a whole not very open. Resin 

 passages few, not very large, with thyloses ; the epithelium of small, 

 thick-walled cells, resinous. Medullary rays not very numerous, prom- 

 inent or broad, i cell wide, distant 2-9 rows of tracheids, more 

 rarely 1 1 . 



Radial. Rays somewhat resinous locally ; the ray tracheids prominent, 

 marginal, rarely interspersed. Parenchyma cells somewhat contracted 

 at the ends, equal to 6-10 spring tracheids ; the terminal walls coarsely 

 pitted ; the upper and lower walls medium or thin and entire, or in 

 the resinous cells and summer wood becoming thicker and pitted ; the 

 lateral walls with rather few and small, narrowly bordered pits with a 

 lenticular orifice, 1-3, more rarely 4, per tracheid, in the summer wood 

 reduced to 2, and finally to i. Bordered pits in i row, elliptical, large; 

 the orifice large and round or lenticular, in the summer wood becoming 

 narrow and parallel with the tracheid axis. Pits on the tangential walls 

 of the summer wood few, small, and chiefly or wholly confined to the 

 outermost tracheid wall. 



Tangential. Rays medium to high, somewhat resinous. The fusiform rays 

 narrow, the resin canal small, with small and thick-walled epithelium 

 cells. Ordinary rays rather broad, conspicuously contracted at the 

 position of the narrow and occasionally interspersed tracheids ; the 

 parenchyma cells equal but variable from round to oval or oblong. 



A large tree of great economic value, 46-61 m. high, with a trunk 2.40 



5.19 m. in diameter. 

 Wood light, soft, not strong, close and straight grained, compact, satiny. 



Relative specific gravity 0.4287 



Percentage of ash residue 0.17 



Approximate relative fuel value 42.80 



Coefficient of elasticity in kilograms on millimeters . . 99. 



Ultimate transverse strength in kilograms 277. 



Ultimate resistance to longitudinal crushing in kilograms 5653. 



Resistance to longitudinal crushing to 1.27 mm. in kilograms 1 160. 

 (Sargent) 



Chiefly confined to the coast of British Columbia, where it attains large 

 size (Macoun) ; Alaska, south to Mendocino County, California, not 

 extending more than 50 miles inland from the coast (Sargent). 



17. * PINUS, TOURN. 



Transverse. Growth rings usually broad. The more or less prominent 

 summer wood variable. Resin passages prominent, chiefly large, with 

 prominent thyloses and thin-walled, variable, several-layered epithe- 

 lium. Resin cells wholly wanting. 



Radial. Ray tracheids prominent and always limiting the ray, often inter- 

 spersed, sometimes predominant, and in rays only a few elements 

 high, commonly constituting the entire structure ; the upper and lower 

 walls often dentate (Sec. II), the teeth sometimes united across the 

 tracheid so as to form more or less prominent reticulations. Ray cells 



