250 ANATOMY OF THE (rVMNOSPERMS 



the lateral walls with 1-4 pits per tracheid. Bordered pits numerous, 

 in I row, round or vertically compressed in compact rows, the len- 

 ticular orifice large. Pits on the tangential walls of the summer 

 tracheids numerous and prominent. Resin cells not very numerous, 

 15-20 p. wide and 150-275 //, long. 



Tangential. Rays usually very low, the cells oval to oblong, not broad, 

 chiefly oval, barely resinous. 



A tree 11-15 m. in height, with a trunk upwards of .30 m. in diameter. 

 Wood light, hard, not strong, very close grained, compact, very durable 

 in contact with the soil. 



Relative specific gravity 0.6907 



Percentage of ash residue 0.47 



Approximate relative fuel value 68.75 



Coefficient of elasticity in kilograms on millimeters . . 734. 



Ultimate transverse strength in kilograms 200. 



Ultimate resistance to longitudinal crushing in kilograms 8505. 



Resistance to indentation to 1.27 mm. in kilograms . . 4464. 

 (Sargent) 



Valley of the Colorado River, western Texas (Sargent). 



7. J. communis, Linn. 

 Juniper. Ground Cedar 



Transverse. Growth rings medium, very variable. The chiefly thin and 

 dense summer wood often double, sometimes equal to the spring 

 wood, into which it passes very gradually, the line of demarcation 

 obscure. Tracheids of the usually broad spring wood small. Resin 

 cells rather numerous, usually not very prominent, in 1-3 very narrow 

 zones in each growth ring, the contiguous tracheids rarely becom- 

 ing resinous so as to form a strongly resinous zone. Medullary 

 rays numerous, i cell wide, distant 2-8, or more rarely 10, rows of 

 tracheids. 



Radial. Rays uniformly resinous throughout, tracheids occasionally pres- 

 ent and marginal. Ray cells somewhat contracted at the ends, equal 

 to 5-6 spring tracheids ; the upper and lower walls thick, unequal, 

 rather frequently pitted ; the terminal walls thin, entire, locally thick- 

 ened or sometimes coarsely pitted ; the lateral walls with unequally 

 bordered, oval pits having a large, lenticular orifice, 1-2 per tracheid. 

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

 not very large or prominent. Resin cells 12.5-15 /j. wide, 125-200/11 

 long. Bordered pits round, equal to the tracheid, in i row, rather 

 distant, or when more crowded becoming elliptical. 



Tangential. Rays numerous, low, narrow, resinous ; the oblong cells thick- 

 walled. 



A prostrate shrub with ascending branches, forming dense mats upwards 

 of 5-7 m. in diameter and 1-1.30 m. high. 



