Spring-shoots slender, pruinose. Leaves in fascicles of three, the sheath revolute at the base, then deciduous; stomata ventral, or ventral and dorsal; resin-ducts external. Scales of the conelet minutely mucronate. Cones from 6 to 9 cm. long, cylindrical, pendent on long peduncles; apophyses lustrous ochre-yellow, elevated in the centre, the umbo usually retaining the small prickle; seed large, bearing on its dorsal surface remnants of the spermoderm. A small bushy tree with long slender branchlets, clear gray cortex, persistently smooth except on the lower part of the trunk, and glaucous-green foliage. It grows along water-courses, dry in autumn and winter, from southern Coahuila to central Hidalgo, and is associated with P. cembroides, from which it may be distinguished by its longer leaves and much longer cylindrical cone. Plate XIII. Fig. 127, Cone, cone-scale and seed. Fig. 128, Branchlet with leaves. Fig. 129, Magnified leaf-section. 15. PINUS NELSONII 1904 P. Nelsonii Shaw in Gard. Chron. ser. 3, xxxvi. 122, f. 49. Spring-shoots slender, pruinose; branchlets very pliant and tough, summer-shoots abundant. Leaves with a persistent sheath, from 6 to 9 cm. long, united in threes along a portion of their ventral surface into pseudomonophyllous fascicles, serrulate on the two margins of the dorsal surface, entire on the ventral margin; stomata dorsal and with one row along the free portion of each ventral face. Conelets usually, if not always, pseudolateral by reason of the summer growth of the branchlets, and attaining in their first season an unusually large size. Cones from 6 to 12 cm. long, on very long stout and curved peduncles, cylindrical, deciduous by an articulation between the cone and its peduncle, leaving the latter for several years on the tree; apophyses dark lustrous orange-red, rugose, elevated along a sharp transverse keel, the umbo obscurely defined, the mucro usually broken away; nuts large, flaxen yellow, the spermoderm adnate to the cone-scale. A small bushy tree with long pliant branches, clear gray cortex all over the limbs and trunk, and sparse gray-green foliage. It grows, together with P. cembroides, on the lower slopes of the northeastern Sierras of Mexico, near the boundary between the states of Tamaulipas and Nuevo Leon. It is apparently confined to a small area near the latitude of the city of Victoria, the capital of Tamaulipas, where its nuts are often exposed for sale. In many characters this species is unique. It can be recognized at once by the connate leaves that form the fascicle or by the remarkable stout curved peduncle of its cone. Such seeds as I have seen differ from those of P. cembroides by a reddish area at one end, but this can be seen with fresh seeds only. Plate XIII. Fig. 124, Cone, cone scale and seed. Fig. 125, Branchlet with leaves. Fig. 126, Magnified section of a leaf-fascicle.