Bark of the branches and upper trunk smooth. 22. P. glabra (C). Bark of the branches and upper trunk roughened. 23. P. echinata (A, C). Cones about 3′ long, armed with persistent spines. Cone-scales armed with slender or stout prickles. Cone-scales evenly developed, their prickles slender, acuminate, from a broad base; leaves 3′ long or less. Cones opening at maturity. 24. P. virginiana (A, C). Cones often remaining closed for many years. 25. P. clausa (C). Cone-scales unevenly developed and armed with stout prickles; cones 2′—3½′ long, remaining closed; leaves 4′—6′ long. 26. P. muricata. Cone-scales armed with very stout hooked spines; cones 2½′—3′ long; opening in the autumn or remaining closed for two or three years; leaves 2′ long or less. 27. P. pungens. Leaves in 5-leaved clusters; cones 4′—6′ long, unsymmetrical, their scales thick; seeds longer than their wings; leaves stout, 9′—13′ long. 28. P. Torreyana (G). 9. Pinus leiophylla Schlecht. and Cham. Yellow Pine. _Pinus chihuahuana_, Engelm. [Illustration: Fig. 12] Leaves slender, pale glaucous green, marked by 6—8 rows of conspicuous stomata on each of the 3 sides, 2½′—4′ long, irregularly deciduous from their fourth season, their sheaths deciduous. Flowers: male yellow; female yellow-green. Fruit ovoid, horizontal or slightly declining, long-stalked, 1½′—2′ long, becoming light chestnut-brown and lustrous, maturing at the end of the third season, with scales only slightly thickened, their ultimately pale umbos armed with recurved deciduous prickles; seeds oval, rounded above and pointed below, about ⅛′ long, with a thin dark brown shell, their wings ⅓′ long and broadest near the middle. A tree, rarely more than 40°—50° high, with a tall trunk sometimes 2° in diameter, stout slightly ascending branches forming a narrow open pyramidal or round-topped head of thin pale foliage, and slender bright orange-brown branchlets, soon becoming dull red-brown. Bark of old trunks ¾′—1½′ thick, dark reddish brown or sometimes nearly black, and deeply divided into broad flat ridges covered with thin closely appressed scales. Wood light, soft, not strong but durable, light orange color, with thick much lighter colored sapwood. Often forming coppice by the growth of shoots from the stump of cut trees.