PINUS 307 



reduced to 2, and finally to I, per tracheid, when they take the form of 

 very narrow and much prolonged slits. Bordered pits in i row, 

 numerous. Pits on the tangential walls of the summer wood small 

 and numerous, extending far into the summer wood. Resinous tra- 

 cheids wanting. 



Tangential. Fusiform rays numerous, very narrow, usually high, the cells 

 'of the inflated portion very thin-walled and chiefly wanting, except 

 the persistent, thicker-walled central tract, which includes a small 

 resin canal. Ordinary rays numerous, medium, somewhat resinous, 

 rather broad, not perceptibly contracted by the occasionally inter- 

 spersed, equal, but higher and oblong tracheids ; the cells thick-walled, 

 very equal, chiefly very uniform, and narrowly oval or oblong, rarely 

 broader. Resinous tracheids wanting. 



A small tree 6-7 m. high, with a trunk rarely exceeding .30 m. in diameter. 

 Wood light, soft, very close grained, and compact. 



Specific gravity 0.6512 



Percentage of ash residue 0.90 



(Sargent) 



Dry ridges and slopes at 3300 feet elevation. Santa Catalina Mountains of 

 Arizona and through northern Mexico (Sargent). 



3. P. monophylla, Torr. 



Pinon. Nut Pine 



Transverse. Growth rings thin, unequal, often double. Summer wood thin, 

 of 3-5 tracheids and open, the tracheids in more or less irregular rows, 

 unequal. Spring tracheids squarish-hexagonal, rather variable, not 

 large, the walls rather thin and commonly showing the secondary wall 

 infolded. Medullary rays not very prominent, numerous, broad, i cell 

 wide, distant 1-6, or more rarely 10, rows of tracheids. Resin passages 

 very large and numerous, the several-layered epithelium composed of 

 large and variable cells, both thick- and thin-walled. 



Aadial. Rays nonresinous ; the tracheids numerous, marginal, often inter- 

 spersed. Parenchyma ray cells short, strongly contracted at the ends ; 

 the terminal walls commonly thick and coarsely pitted ; the upper and 

 lower walls thick and strongly pitted ; the lateral walls with more or 

 less obviously-bordered pits, with a prolonged, slit-like orifice which 

 becomes lenticular in the earlier spring wood, 1-4, chiefly 4, per tra- 

 cheid, finally reduced to 2 in the outer summer wood. Bordered pits 

 numerous, in i row, elliptical. Pits on the tangential walls of the sum- 

 mer wood numerous, medium to large, conspicuously lenticular. Res- 

 inous tracheids wanting. 



Tangential. Fusiform rays rather numerous and narrow, the cells of the 

 'inflated portion large and very thin-walled, often much broken out, the 

 persistent central tract containing a resin canal of medium size. Ordi- 

 nary rays numerous, broad, very sparingly resinous, not contracted by 

 interspersed tracheids ; the cells conspicuously unequal and variable, 



