PINUS 293 



and equal tracheids ; the cells very equal, chiefly very 

 uniform, narrowly oval or oblong, rarely broader. 



2. P. cembroides. 



Pits on the lateral walls of the ray cells 1-5 throughout, or finally 

 12, per tracheid in the summer wood. 



Ordinary rays rather broad and nonresinous (tangential), 

 somewhat contracted by the narrower and smaller, occasion- 

 ally interspersed tracheids ; the cells very equal and uniform, 

 narrowly oval to oblong. 



4. P. Balfouriana. 



Ray cells (radial) of 2 kinds: (i) thick-walled and strongly pitted; 

 (2) thin-walled, devoid of pits, conterminous, and interspersed. 



Pits on the lateral walls of the ray cells 3-6, soon 4, or in the outer 

 summer wood 2, per tracheid. 



Ordinary rays (tangential) nonresinous, numerous, the cells equal, 

 uniform, oval, or oblong. 



Fusiform rays (tangential) few, narrow. 



5. P. aristata. 



Pits on the lateral walls of the ray cells 1-4 throughout, or in the 

 marginal cells upwards of 5 or 6, per tracheid. 



Ordinary rays (tangential) numerous, broad, the cells chiefly equal, 

 uniform, oval, and narrow. 



Fusiform rays (tangential) rather numerous, small, and narrow. 



6. P. edulis. 



B. Lateral walls of the ray cells (radial) with large, open, and 

 simple, oval, or lenticular pits, 1-2 per tracheid; the upper 

 and lower walls thin and distantly or even obscurely pitted; 

 the terminal walls thin and entire or locally thickened ; the 

 thin side walls (tangential) either inflated or incurved. 

 Ray cells (transverse or tangential) with their very thin side walls strongly 

 inflated and projecting into the cavities of the adjacent tracheids. 



Pits on the lateral walls of the ray cells oval or squarish, or finally 

 lenticular, 1-2, chiefly i, per tracheid throughout. 



Resin passages numerous and large, chiefly in or near the summer 

 wood ; when in the former situation, central to a large tract of 



thin-walled tracheids. 



10. P. reflexa. 



Ray cells (transverse or tangential) with their thin side walls not strongly 

 inflated, but commonly incurved or sometimes convex. 



Pits on the lateral walls of the ray cells chiefly 1-2 per tracheid. 

 Resinous tracheids (radial) not present. 



Rays (tangential) strongly resinous, the cells oval, unequal, 

 variable. 



