SUMMER KEY TO THE SPECIES OF PINUS 



a. Leaves 5 in a cluster; cones 4-10 inches long 



P. strobus, p. 7. 



aa. Leaves 2 in a cluster; cones less than 4 inches long, 

 b. Leaves 1-3 inches long. 



c. Leaves about I inch long, divergent; cones sessile, point- 

 ing forward towards the tip of the branch, persistent 

 10-15 years, opening very unevenly. . .P. banksiana, p. 9. 

 cc. Leaves 1/^-3 inches long, slightly divergent; cones stout- 

 stalked, pointing away from the tip of the branch, 



maturing in second season, opening evenly 



P. sylvestris, p. 13. 



bb. Leaves 3-6 inches long. 



c. Bark of trunk red-brown ; cones maturing in second 

 season, about 2 inches long; cone-scales thickened at the 



apex, but unarmed P. resinosa, p. 15. 



cc. Bark of trunk gray to nearly black; cones maturing in 

 first season, 2-3 inches long; cone-scales thickened at the 



apex and topped with a short spine. 



P. laricio austriaca, p. 1 1. 



