296 ANATOMY OF THE GYMNOSPERMS 



Ray tracheids strongly predominant and 

 strongly reticulated throughout. 



i 7. P. Banksiana. 



Fusiform rays (tangential) with the cells of the inflated portion all or 

 chiefly thin-walled, all broken out. 



Epithelium of the resin passages (transverse) chiefly or wholly in 

 i row, nonresinous (rarely resinous in P. taeda and P. rigida). 

 Summer wood open. 



Bordered pits in i row, sometimes in pairs. 



Pits on the lateral walls of the ray cells 1-5, chiefly 

 2, per tracheid, becoming bordered in the summer 

 wood. 



Ray tracheids sparingly interspersed, strongly 

 reticulated throughout. 



15. P. rigida. 



Pits on the lateral walls of the ray cells 1-4, rarely 5, 

 per tracheid. 



Ray tracheids more or less reticulated in the 

 summer wood, often interspersed. 



25. P. Murrayana. 

 Bordered pits in 1-2 rows. 



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

 2-4, per tracheid. 



Ray tracheids sparingly (very rarely strongly) 

 reticulated throughout. 

 39. P. taeda, Linn. 



Pits on the lateral walls of the ray cells i -5 per tracheid. 

 Ray tracheids when interspersed very low, 

 strongly reticulated throughout. 



14. P. clausa. 

 Summer wood dense. 



Bordered pits in 1-2 rows. 



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

 2-4, per tracheid. 



Ray tracheids sparingly (rarely strongly) retic- 

 ulated throughout. 



39. P. taeda. 



Ray tracheids high, very strongly reticulated 

 throughout. 



The ray cells apparently all of i kind, but 

 differentiating slightly. 

 41. P. cubensis. 



