B4 ROYAL SOCIETY OF CANADA 



Tangential. Fusiform rays with linear and often prolonged terminals, 

 the cells small and thick-walled, the central tract of one small resin- 

 passage without, more rarely with, thyloses, but with thick-walled 

 epithelium. Cells of the ordinary ray oblong, more rarely oval, the 

 walls medium. 



Species. 



1. P. rubra, Link. 4. P. sitchensis, Trautv. and Mey. 



2. P. nigra, Link. 5. P. piaigens, Engelm. 



3. P. alba. Link. 6. P. Engelmanni, Engel. 



12. PiNus, Tourn. 



Transverse. Growth-rings chiefl}^ broad. Summer wood variable, but 

 usually more or less prominent. Eesin-passages prominent but scat- 

 tering, with thin-walled and variable epithelium, and with prominent 

 thyloses. Eesin-cells wholly wanting. 



Madial. Eay tracheids prominent and always limiting the ray, often 

 interspersed, sometimes prominent; the upper and lower walls often 

 dentate, the teeth sometimes united across the tracheid so as to form 

 more or less prominent reticulations. Ray-cells of one or two kinds. 

 Bordered pits on the tangential walls of the summer tracheids either 

 numerous or wholly wanting. Tracheids without spirals. 



Tangential. Eays of two kinds ; the fusiform rays chiefly large and 

 broad, the cells of the inflated portion chiefly large and mostly thin- 

 walled, the central tract of one large resin-passage with thyloses. 

 Ordinary rays almost strictly uni-seriate. 



Species. 

 1. Pits on the tangential walls of the summer wood. 



1. P.fl,exilis, .Tames. 7. P. Parryawa, Engel. 



2. P. vionticola, Dougl. 8. P. cembroides, Zucc. 



3. P. Lambertlana, Dougl. 9. P. tnonophylla, Torr. and Fren. 



4. P. albicaulis, Engel. 10. P. Balfuvriana, Murr. 



5. P. rejleaca, Engel. " " var. aristata, Engel. 



6. P. strobus, L. 11. P. edulis, Engel. 



2. Pits on the tangential walls of the summer wood wanting. 



12. P. resinosa. Ait. 24. P. contorta, Dougl. 



13. P. Murrayana, Balf. 25. P. glabra, Walt. 



14. P. arizonica, Engel. 26. P. inoj),% Ait. 



15. P. Coulteri, D. Don. 27. P. r-tsr<t7a,Mill. 



16. P. Sabiniana, Dougl. 28. P. 2}ungens, Michx, f. 



17. P. chihuuliuana, Engel. 29. P. serotina, Michx. 



18. P. Jejfreyi, Murr. 30. P. taeda, L. 



19. P. jwnderosa, Dougl. 31. P. clausa, Vasey. 

 " " var. scopulorum, Engl. 32. P. palustris, Mill. 



20. P. muricata, D. Don. 33. P. Banksiana, Lamb. 



21. P. tuberculata, Gord. 34. P. echinata. Mill. 



22. P. Torreyana, Parry. 35. P. cubensis, Griseb. 



23. P. insignis, Dougl. 



