Spring-shoots glabrous or temporarily pubescent. Leaves from 2 to 4 cm. long, persistent for many years; stomata ventral only; resin-ducts external. Scales of the conelet prolonged into long slender bristles. Cones from 4 to 9 cm. long, subcylindrical or tapering to a rounded apex, short-pedunculate; apophyses terracotta or purple-brown, tumid, the long bristles of the umbo often partly or wholly broken away; seeds with a long articulate wing. A bushy tree, similar in foliage to the preceding species, growing at the timber-limit from Colorado through Utah, central and southern Nevada and northern Arizona into southeastern California, but separated from the nearest station of P. Balfouriana by an arid treeless desert. Engelmann (in Brewer and Watson, Bot. Calif. ii. 125) considered it to be a variety of P. Balfouriana. Plate XV. Fig. 143, Cone. Fig. 144, Seed and enlarged cone-scale. Fig. 145, Leaf-fascicle and magnified leaf-section. Fig. 146, Conelet. [Illustration: PLATE XV. P. ARISTATA (143-146), BALFOURIANA (147-150)] DIPLOXYLON Bases of the bracts subtending leaf-fascicles decurrent. Leaves serrulate; fibro-vascular bundle double; stomata dorsal and ventral. Cones with a dorsal umbo, the phyllotaxis complex. Wood hard, with dark resinous bands, the annual rings clearly defined. In this section there are a few species combining the essential characters of Diploxylon with important characters of Haploxylon. A subsection, Parapinaster, is established for these exceptional species. c. Parapinaster Species with the fascicle-sheath or seed-wing of Haploxylon. d. Pinaster Sheath persistent, seed-wing articulate, effective. =Parapinaster= Sheath of the leaf-fascicle deciduous VII. Leiophyllae. Sheath of the leaf-fascicle persistent. Seed-wing of the Strobi VIII. Longifoliae. Seed-wing of the Gerardianae IX. Pineae. =VII. LEIOPHYLLAE= Sheath of the leaf-fascicles deciduous. Leaves short, erect, the fructification triennial 20. leiophylla. Leaves long, pendent, the fructification biennial 21. Lumholtzii. 20. PINUS LEIOPHYLLA 1831 P. leiophylla Schlechtendal and Chamisso in Linnaea, vi. 354. 1848 P. chihuahuana Engelmann in Wislizenus, Tour. Mex. 103. Spring-shoots uninodal. Leaves in fascicles of 3, 4 or 5, the sheath deciduous, from 8 to 14 cm. long; resin-ducts medial with an occasional internal duct. Conelets single or verticillate, their scales mucronate; conelets of the second year only slightly enlarged. Cones maturing the third year, not exceeding 7 cm. in length, ovate or ovate-conic, subsymmetrical, more or less reflexed, persistent for several years on some trees, sometimes serotinous; apophyses lighter or darker brown, often with an olive or fuscous shade, thin or tumid, the umbo double, the mucro more persistent near the apex of the cone.