41 



*^ 



Cones oval or elongated ; scales armed ; seeds much 

 shorter than the wing. — Balfoiiriana. 



19. P. Balfouriana, (20. artistata.) 



4. Sylvestres. — Leaves serrulate, their sheaths persistent. —Europe- 



and Asia, one species in America. 



^* Leaves in threes. — Fudicae. ■ 



21. P, Khasia, 22. insularis, 23. longifolia. 



^'^ Leaves in twos. Cones and seeds small ; wings large. 

 Eusylvestres. 



I 



24. P. sylvestris, 25 montana, 26. resinosa, 27. densiflora, 

 28. Massoniana, 29. ? Merkusii. 



^■^'^ Leaves in twos. Cones and seeds large; wings rudi- 

 mentary. A single Mediterranean species. 



30. P. Pinea. 



b. Cones lateral. • 



5. Halepenses.— Old World. 



* Leaves in threes ; sheaths deciduous ; umbo very promi- 

 nent ; wings shorter than the large seeds. Gerardianae, — Asia. 



3r. P. Gerardiana, 32. Bungeana. 



■^^ Leaves in twos; sheaths persistent ; cones smoothish ; 

 wings much longer than seeds. Euhalcpenses. — Mediterranean 

 regions. 



3, P. Halepensis, 34. Pyrenaica. 



B. Ducts parenchymatous, a. Cones subterminal. 

 6, Ponderosae. — Mostly American with three Old World species. 



* Leaves in fives ; ducts usually free of strengthening cells; 

 Psetidostrobi, — Central America and Mexico to Arizona and 

 California. 



35. P. leiophylla, -xfi. tenuifolia, 37. filifolia, 38. Pseudo- 

 Strobus, 39. Montezumae, (40. Hartwegii), 41. Torreyana, 

 42. Arizonica. 



** Leaves in threes, sometimes in fours or fives ; sheaths 

 persistent; strengthening cells under the epidermis, around 

 ducts. Euponderosae, — Northwestern America, Mexico and 

 Canary Islands. 



43. P. Engelmanni, 44. ponderosa, (45. Jeffreyi), 46. Cana- 



riensis. 



*** Leaves in threes ; slieaths deciduous. — Mexico and 

 Arizona. 



