PINUS $99 



Ray tracheids high, very strongly reticulated 

 throughout. 



Ray cells apparently all of one kind, but 



differentiating slightly. 

 41. P. cubensis. 



Pits on the lateral walls of the ray cells 1-6 per 

 tracheid. 



Ray tracheids strongly predominant and strongly 

 reticulated throughout. 



17. P. Banksiana. 



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

 per tracheid. 



Ray tracheids sparingly interspersed, strongly 

 reticulated throughout. 



16. P. serotina. 



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, chiefly 

 2, per tracheid. 



Ray tracheids sparingly interspersed, distinctly 

 reticulated throughout. 



1 8. P. contorta. 



Ray cells (radial) of 2 kinds: (i) thick-walled ; and (2) thin-walled. 



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

 chiefly thick-walled. 



Epithelium of the resin passages (transverse) in 1-2 or more rows, 

 nonresinous. 



Summer wood dense. 



Bordered pits in i row or sometimes in pairs. 



Pits on the lateral walls of the ray cells (i) 1-3, 

 bordered in the summer wood; and (2) 1-4, chiefly 

 2-3, per tracheid. 



Ray tracheids more or less interspersed, retic- 

 ulated throughout. 



34. P. pungens. 



Epithelium of the resin passages (transverse) in 1-2 or more rows, 

 resinous. 



Summer wood open. 



