302 ANATOMY OF THE GYMNOSPERMS 



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. 

 Bordered pits in 1-2 rows. 



Pits on the lateral walls of the ray cells 2-5, chiefly 

 4, per tracheid. 



Ray tracheids commonly predominant and inter- 

 spersed, very strongly reticulated throughout. 



40. P. palustris. 



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

 2-4, per tracheid. 



Ray tracheids high, very strongly reticulated 

 throughout. 



41. P. cubensis. 



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

 rows, resinous. 



Summer wood dense. 



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 interspersed, often predominant, 

 sparingly reticulated. 



19. P. glabra. 



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

 tracheid, rarely 5. 



Ray tracheids strongly reticulated, often pre- 

 dominant. 



32. P. ponderosa. 

 Bordered pits in i row, sometimes in pairs. 



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. 



Pits on the lateral walls of the ray cells (i) 2-6, 

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

 Ray tracheids predominant, very strongly retic- 

 ulated throughout. 

 35. P. inops. 



