3 oo ANATOMY OF THE GYMNOSPERMS 



Bordered pits in i row or 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 (i) 1-4; and 

 (2) 1-3, chiefly 2, per tracheid, the two forms of 

 cells clearly defined. 



Ray tracheids reticulated in the summer wood, 

 predominant in the low rays of which they 

 often compose the entire structure. 



36. P. muricata. 



Pits on the lateral walls of the ray cells 2-4 through- 

 out, the two forms of cells merging and not always 

 clearly defined. 



Ray tracheids strongly dentate and becoming 

 sparingly reticulated in the summer wood, 

 interspersed, often predominant. 



30. P. chihuahuana. 

 Summer wood dense. 



Bordered pits in i row or sometimes in pairs. 



Pits on the lateral walls of the ray cells 2-4 through- 

 out, the two forms of cells merging and not always 

 clearly differentiated. 



Ray tracheids strongly dentate and becoming 

 sparingly reticulated in the summer wood, 

 interspersed, often predominant. 



30. P. chihuahuana. 



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

 thin-walled and usually broken out. 



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

 nonresinous. 



Summer wood open. 



Bordered pits in I row. 



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

 2 or 3, per tracheid, but very variable. 



Ray tracheids interspersed, often predominant, 

 sparingly reticulated. 



19. P. glabra. 



Pits on the lateral walls of the ray cells (i) 1-4 ; and 

 (2) 2-4, chiefly 4, per tracheid. 



