SUMMER KEY TO THE SPECIES OF PINUS 
a. Leaves 5 in a cluster; cones 4-10 inches long.........++++ 
Siaeaklath: Dea aay teee cena ee Mens oe nea P. strobus, p. 7. 
aa. Leaves 2 in a cluster; cones less than 4 inches long. 
b. Leaves 1-3 inches long. 
Cc. 
cc. 
Leaves about 1 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. 
Leaves 114-3 inches long, slightly divergent; cones stout- 
stalked, pointing away from the tip of the branch, 
maturing in second season, opening evenly............ 
Smiauaatmunace dae Cate CaveMNaed eae ta es P. sylvestris, p. 13. 
bb. Leaves 3-6 inches long. 
c 
cc. 
Bark of trunk red-brown; cones maturing in: second 
season, about 2 inches long; cone-scales thickened at the 
apex, but unarmed................0006 P. resinosa, p. 15. 
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.................5. 
saaeen ys Ube ied 5 HMSONER ER Eee P. laricio austriaca, p. 11. 
