P. albicaulis is distinguished from its allies by its entire leaves with both dorsal and ventral stomata, from P. flexilis by its indehiscent cone, and from all of these species by its seed without membranous cover or rudimentary wing. It was united with P. flexilis by Parlatore and Gordon, and, later, was referred to that species as a varietal form by Engelmann (in Brewer & Watson, Bot. Calif. ii. 124). Parrish's P. albicaulis (in Zoe, iv. 350), extending its range to the mountains of southern California, proves to be P. flexilis (Jepson, Silva Calif. 74). Plate VIII. Fig. 90, Two cones and seed. Fig. 91, Leaf-fascicle. Fig. 92, Magnified leaf-section. [Illustration: PLATE VIII. P. KORAIENSIS (85, 86), CEMBRA (87-89), ALBICAULIS (90-92)] =II. FLEXILES= Seeds wingless, the spermoderm forming a narrow border with a rudimentary prolongation. Cones dehiscent at maturity. The dehiscent cone distinguishes this group from the Cembrae. Therefore confusion of P. koraiensis with P. Armandi, or P. albicaulis with P. flexilis should be impossible. The peculiar seed is found again only in the northern variety of P. ayacahuite. Leaves usually entire, the stomata dorsal and ventral 4. flexilis. Leaves serrulate, the stomata ventral only 5. Armandi. 4. PINUS FLEXILIS 1823 P. flexilis James in Long's Exped. ii. 34. 1882 P. reflexa Engelmann in Bot. Gaz. vii. 4. 1897 P. strobiformis Sargent, Silva N. Am. xi. 33, tt. 544, 545 (not Engelmann). Spring-shoots pubescent; branchlets very tough and pliant. Leaves from 3 to 9 cm. long, entire, or serrulate in the southern variety, persistent for five or six years; stomata dorsal and ventral or, in the south, sometimes ventral only; resin-ducts external. Cones from 6 to 25 cm. long, ovate or subcylindrical, short-pedunculate; apophyses pale tawny yellow, or yellow ochre, lustrous, often prolonged and more or less reflexed, thick, the margin together with the umbo raised above the surface of the cone. This species grows on the Rocky Mountains from Alberta in the Dominion of Canada to Chihuahua in northern Mexico and ranges westward to the eastern slope of the Sierras and to the southern mountains of California. The wood, where accessible, is manufactured into lumber. It may be seen in the Arnold Arboretum and in the Royal Gardens at Kew.