PINUS 295 



A. Pits on the lateral walls of the ray cells large and open, 

 chiefly i, and not exceeding 2, per tracheid. 



Ray cells of i kind only. 



Pits on the lateral walls of the ray cells simple throughout. 

 Epithelium of the resin passages resinous. 



Bordered pits in i row, sometimes in pairs. 



Ray tracheids simply dentate, rarely interspersed. 



Pits on the lateral walls of the ray cells 1-2, chiefly 

 i, per tracheid. 



21. P. resinosa. 



Ray tracheids simply dentate, but numerous and inter- 

 spersed and often predominant. 



Pits on the lateral walls of the ray cells large, oval, 

 oblong, or lenticular, 1-2, chiefly i, per tracheid. 



22. P. tropicalis. 



Pits on the lateral walls of the ray cells large and conspicuously bor- 

 dered in the summer wood. 



Epithelium of the resin passages nonresinous. 



Resin passages (transverse) large, numerous, scattering. 

 Bordered pits in i row. 



Ray tracheids (radial or tangential) simply dentate, 

 not interspersed. 



Pits on the lateral walls of the ray cells i, 

 rarely 2, per tracheid. 



23. P. Thunbergii. 



Ray tracheids (radial or tangential) somewhat inter- 

 spersed, sparingly reticulated in the summer wood. 

 Pits on the lateral walls of the ray cells strictly 

 i per tracheid. 



24. P. densiflora. 



B. Pits on the lateral walls of the ray cells generally rather 

 small and upwards of 6 per tracheid, at least 2 or more per 

 tracheid. 



Ray cells (radial) of I kind only and thin-walled. 



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

 chiefly rather thick-walled. 



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

 resinous. 



Summer wood dense. 



Bordered pits in i row, or sometimes in pairs. 



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

 cheid. 



