Leaves in 5-leaved clusters. Cones long-stalked, elongated, cylindric bright green at maturity, becoming light yellow brown, their scales thin, with terminal unarmed umbos; seeds shorter than their wings. White Pines. Leaves without conspicuous white lines on the back. Leaves slender, flexible; cones 4′—8′ long. 1. P. Strobus (A). Leaves stout, more rigid; cones 5′—11′ long. 2. P. monticola (B, G). Leaves with conspicuous white lines on the back; cones 12′—18′ long. 3. P. Lambertiana (G). Cones short-stalked, green or purple at maturity, their scales thick. Cones cylindric or subglobose, their scales with terminal umbos; leaves 2′ long or less. Stone Pines. Cones 3′—10′ long, their scales opening at maturity; seeds with wings. 4. P. flexilis (F, H). Cones ½′—3′ long, their scales remaining closed at maturity; seeds wingless. 5. P. albicaulis (B, F, G). Cones ovoid-oblong, their scales with dorsal umbos armed with slender prickles; seeds shorter than their wings; leaves in crowded clusters, incurved, less than 2′ long. Foxtail Pines. Cones armed with minute incurved prickles. 6. P. Balfouriana (G). Cones armed with long slender prickles. 7. P. aristata (F, G). Leaves in 1—4-leaved clusters; cones globose, green at maturity, becoming light brown, their scales few, concave, much thickened, only the middle scales seed-bearing; seeds large and edible, their wings rudimentary; leaves 2′ or less, often incurved. Nut Pines. 8. P. cembroides (C, F, G, H). 1. Pinus Strobus L. White Pine. [Illustration: Fig. 1] Leaves soft bluish green, whitened on the ventral side by 3—5 bands of stomata, 3′—5′ long, mostly turning yellow and falling in September in their second season, or persistent until the following June. Flowers: male yellow; female bright pink, with purple scale margins. Fruit fully grown in July of the second season, 4′—8′ long, opening and discharging its seeds in September; seeds narrowed at the ends, ¼′ long, red-brown mottled with black, about one fourth as long as their wings.