52 CONTRIBUTIONS FROM THE NATIONAL HERBARIUM. 



Sheaths of the leaves persistent. 

 Cones usually deciduous, dull or sublustrous. 

 Cones 4 to 5 cm. long. 



Leaves bright green 14. P, teocote. 



Leaves glaucous 15. P. lawsoni. 



Cones mostly 8 to 30 cm. long. 

 Leaves in fascicles of 3 or 4 ; cones 6 to 12 cm. long. 



Sheaths deciduous 12. P. chihuahuana. 



Sheaths persistent. 

 Cones deciduous, dull. 



Cones 7 cm. long or shorter 14. P. teocote. 



Cones 6 to 12 cm. long 18. P. hartwegii. 



Cones persistent, sublustrous. 



Leaves 8 to 13 cm. long; cones 4 to 8 cm. long; resin ducts 

 uniting hypoderm and endoderm of the leaves. 



23. P. oocarpa. 

 Leaves 7 to 10 cm. long ; cones 6 to 12 cm. long ; resin ducts 



medial 24. P. greggii. 



Leaves in fascicles of 5. 

 Cones 4 to 12 cm. long. 



Sheaths deciduous 11. P. leiophylla. 



Sheaths persistent. 

 Leaves 18 to 28 cm. long. Cones persistent, lustrous. 



23. P. oocarpa. 

 Leaves 7 to 18 cm. long. 



Cones deciduous, dull 18. P. hartwegii. 



Cones persistent, lustrous 20. P. arizonica. 



^ Cones 10 to 45 cm. long. 



Leaves 10 to 20 cm. long 7. P. ayacahuite. 



Leaves less than 10 cm. long. 



Leaves entire. Seed wings rudimentary 8. P. flexilis. 



Leaves serrulate. 



Prickles of the cone scales weak and deciduous. 



Bark of young trees smooth 16. P. pseudostrobus. 



Bark of young trees rough 17. P. montezumae. 



Prickles of the cone scales stout and persistent. 



19. P. ponderosa. 

 Cones persistent, very lustrous. 



Resin ducts of the leaves uniting the hypoderm and endoderm. 



23. P. oocarpa. 

 Resin ducts of the leaves internal or medial. 

 Resin ducts of the leaves internal. 



Cone scales without upcurved spines 21. P. pringlei. 



Cone scales with strongly upcurved spines 22. P. coulteri. 



Resin ducts medial 25. P. patula. 



l^eaves up to 15 cm. long, usually shorter. 

 Seeds not winged. Leaves in fascicles of 3. 



Sheaths of the leaves deciduous ; leaves entire 5. P. pinceana. 



Sheaths persistent; leaves serrulate 6, P. nelsoni. 



Seeds winged. 

 Seed wing well developed; cones 25 to 45 cm. long. 



9. P. lambertiana. 

 Seed wing rudimentary; cones 10 to 25 era. long 10. P. refiexa. 



