PINUS 333 



which form an irregular tract and outwardly pass into occasional 

 thick-walled cells. Medullary rays broad, i cell wide, not very prom- 

 inent, distant 2-10 rows of tracheids. 



Radial. Rays sparingly resinous, the resin confined to the thin walls ; the 

 tracheids about equal to, or in the low rays exceeding, the parenchyma 

 cells ; rarely interspersed, strongly reticulated throughout. Ray cells 

 of two kinds: (i) cells rather abundant, chiefly straight; the terminal 

 walls thin and entire ; the upper and lower walls thick, coarsely and 

 imperfectly pitted ; the lateral walls with very prominent and round, 

 elliptical or oblong pits which sometimes become distinctly bordered 

 in the summer wood, 2-4, chiefly 4, per tracheid ; and (2) cells broad, 

 fusiform, and variable ; the terminal, upper, and lower walls very thin 

 and much broken down ; the lateral walls with oval or lenticular vari- 

 able pits which become very narrow and often much elongated in the 

 summer wood, 2-3 per tracheid. Bordered pits in i row, sometimes 

 in pairs, elliptical, in the summer wood quickly reduced to 12-14 /A, 

 and finally to 7.2 p.. Pits on the tangential walls of the summer wood 

 wholly wanting. 



Tangential. Fusiform rays rather numerous, small to medium, the terminals 

 acute, rarely somewhat prolonged, usually inflated for the whole 

 height ; the cells of the terminals composed of thick-walled paren- 

 chyma and small tracheids, those of the inflated portion very thin- 

 walled and generally broken out. Ordinary rays low to medium, 

 somewhat numerous, broad, very rarely contracted by the small and 

 much narrower, interspersed tracheids of the highest rays ; thick- 

 walled parenchyma cells few ; thin-walled parenchyma cells predom- 

 inant, resinous, much broken out. 



A low, short-lived, gnarled, and crooked tree 6-8 in. high, with a trunk 



upwards of .33 m. in diameter. 

 Wood light, soft, not strong, brittle, rather close grained, and compact. 



Specific gravity 04879 



Percentage of ash residue . 0.35 



Approximate relative fuel value 50.62 



Coefficient of elasticity in kilograms on millimeters . . 542. 



Ultimate transverse strength in kilograms 323. 



Ultimate resistance to longitudinal crushing in kilograms 4548. 



Resistance to indentation to 1.27 mm. in kilograms . . 2309. 

 (Sargent) 



A very local tree in San Diego County, California, and possibly Lower 

 California and the islands off Santa Barbara (Sargent). 



30. P. chihuahuana, Engelm. 

 Yellow Pine 



Transverse. Growth rings thin, variable. Summer wood thin, variable, 

 the thicker zones dense, the thin zones open ; the transition from the 

 spring wood rather abrupt ; the tracheids in regular rows, variable. 

 Spring tracheids squarish-hexagonal, very unequal in regular rows, 



