304 ANATOMY OF THE GYMNOSPERMS 



Ray tracheids strongly predominant, strongly 

 dentate, and somewhat reticulated in the 

 summer wood. 



26. P. arizonica. 



Pits on the lateral walls of the ray cells (i) 1-6, 

 chiefly 4 ; and (2) 1-4, chiefly 4, per tracheid. 

 Ray tracheids predominant, very strongly retic- 

 ulated throughout. 



35. P. inops. 

 Bordered pits in I row. 



Pits on the lateral walls of the ray cells 1-6, chiefly 

 2 or 3, per tracheid, but very variable. 



Ray tracheids often predominant, interspersed, 

 sparingly reticulated. 

 19. P. glabra. 



B. **PITYOXYLON (Pinoxylon) 



Extinct Species 

 Ray tracheids present. 



Upper and lower walls of the ray tracheids dentate. 

 Bordered pits in 2 rows. 



Resin passages numerous, large, scattering. 



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



42. ** P. (Pinoxylon) dacotense. 

 Upper and lower walls of the ray tracheids not dentate. 



Bordered pits in i row. 



Transition from the spring to the summer wood gradual. 

 Ordinary rays (tangential) 1-2 seriate in part. 

 Resin passages (transverse) very large. 



Medullary rays (transverse) distant 3-8, more 

 rarely 8, rows of tracheids. 



43. ** P. Aldersoni. 

 Ordinary rays (tangential) strictly i-seriate. 



Resin passages (transverse) very large. 



Medullary rays (transverse) distant upwards of 

 25 rows of tracheids. 



44. * * P. amethystinum. 



Resin passages (transverse) rather large, the epi- 

 thelial cells resinous. 



Medullary rays (transverse) distant upwards of 

 9, or rarely 15, rows of tracheids. 



45. ** P. (Pinus) columbiana. 



