CONIFERS 13 



Sheaths of the leaf -clusters deciduous. 



Cones i'-2' long, maturing' in the third year, leaves in 3-leaved clusters, slender, 

 2i'-4' long. 13. P. Chihuahuana (H). 



Sheaths of the leaf-clusters persistent. 



Leaves in o-leaved clusters {S and 2-leaved in 15, 17, and 21, 5-leaved in 14)- 

 Cones subterminal. 



Cones 2'-2i' long ; leaves in 5-leaved clusters. 14. P. Arizonica (H). 



Cones usually deciduous above the basal scales persistent on the branch. 



Buds brown ; leaves in 2 and o-leaved clusters. 15. P. ponderosa (B, F, G, H). 

 Buds white. 16. P. palustris (C). 



Cones lateral. 



Cones symmetrical, their outer scales not excessively developed. 



Young cones reflexed ; leaves in 2 and 3-leaved clusters, 8'-12' long. 



17. P. Caribsea (C). 



Cones oblong, prickles stout ; leaves 6'-9' long. 18. P. Taeda (A, C)- 



Cones ovate, prickles slender. 



Leaves 3'-5' long. 19. P. rigida (A). 



Leaves 6'-8' long. 20. P. serotina (C). 



Cones unsymmetrical by the excessive development of the scales on the outer side. 



Prickles of the cone-scales minute. 21. P. radiata (G). 



Prickles of the cone-scales stout. 22. P. attenuata (G). 



Cones 6'-14' long, their scales prolonged into stout straight or curved spines ; 



leaves long and stout. 



Cones broad-ovate ; seeds longer than their wings. 23. P. Sabiiiiana (G). 

 Cones oblong-conical. . . 24. P. Coulteri (G) 



Leaves in 2-leaved clusters (3 and 3-leaved in 29). 

 Cones subterminal. 



Cones symmetrical, 2'-2| ' long, their scales unarmed ; leaves 5'-6' long, flexible. 



25. P. resinosa (A). 

 Cones unsymmetrical by the greater development of the scales on the outer 

 side, armed with slender prickles; leaves l'-4' long. 



26. P. contorta (B, F, G). 

 Cones lateral. 



Cones about 2' long, mostly unarmed and incurved, their scales very unevenly 

 developed ; leaves less than 2' long. 27. P. divaricata (A). 



Cones about 2' long, their scales evenly developed, armed with weak or decidu- 

 ous prickles ; leaves 4' long or less. 



Bark of the branches and upper trunk smooth. 28. P. glabra (C). 



Bark of the branches and upper trunk roughened. 29. P. echinata (A, C). 

 Cones about 3' long, armed with persistent spines. 



Cone-scales evenly developed, their prickles slender, acuminate, from a broad 

 base ; leaves soft, 3' long or less. 



Cones opening at maturity. 30. P. Virginiana (A, C) 



Cones often remaining closed for many years. 31. P. clausa (C). 



Outer cone-scales excessively developed and armed with stout prickles. 



Cones 2'-3|' long, remaining closed ; leaves 4'-6' long. 32. P. muricata (G). 

 Cone-scales armed with very stout hooked spines. 



Cones 2i'-3' long; leaves 2' long or less. 33. P. pungens (A). 



Leaves in 5-leaved clusters. 



Cones 4-6 long, unsymmetrical, their scales thick ; seeds shorter than their wings ; 

 leaves stout, 9'-13' long. 34. P. Torreyana (G). 



