CONIFERS 13 



Sheaths of the leaf-clusters deciduous. 



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

 long. 13. P. Chihuahuana (H). 



Sheaths of the leaf -clusters persistent. 



Leaves in 3-leaved clusters (-' and ..'-leaved in 15, 17, and 21, 5-leaved in 14)- 

 Cones subterminal. 



CotlM 2*-2f long; leaves in 5-leaved clusters. 14. P. Arizonica (H). 



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



IJuds brown ; leaves in 2 and 3-leaved clusters. 15. P. poilderosa (B, F, G, H). 

 Im.is white. !<> P. paluatris (C). 



Cones lateral. 



( \ini-s symmetrical, their outer scales not excessively developed. 



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



17. P. Caribaea (C). 



( 'ones oblong, prickles stout ; leaves G'-9' long. is. P. Taeda ( A 



Cones ovate, prickles slender. 



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



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



< 'ones 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-sc-ales stout. 22. P. atteiiuata (G). 



( 'ones G'-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. Sabiniaiia 

 ',.ues oblong-conical 24. P. Coulter! (G) 



Leaves iii 2-h-aved clusters (.' and 3-leaved in 29). 

 Cones subterminal. 



Cones symmetrical. 2'-2 1 , ' long, their scales unarmed ; leaves 5'-(i long, flexible. 



_'.">. 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. 



IJark of the branches and upper trunk smooth. 2S. P. glabra (C). 



Hark of the branches and upper trunk nm-hened. 2J>. 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, .'!' long or less. 



Conea opening at maturity. 30. P. Virginiana i 



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



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



Cones 2'-3i' long, remaining close, 1 : leaves I'-d' long. 32. P. muricata (G). 

 Cone-scales armed with very stout hooked spines. 



Cones 2|'-3' long ; leaves 2' long or Lew, 3.",. P. pungeiis (A). 



Leaves in 5-leaved clusters. 



Cones 4 -('' long, unsymmetrical, their scales thick ; seeds shorter than their wings : 

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



