Mature trees of P. strobus tower above the evergreens associated with it. It is also recognized by the color and horizontal massing of its foliage. The cone, when closed, is very narrow; its thin flat scales distinguish it from the cone of P. peuce, and its phyllotaxis from the cone of P. monticola. To illustrate the possibilities of variation in the size of Pine cones, I once collected several in Tamworth, N. H., on the estate of Mr. Augustus Hemenway, on the same slope and within an area of one square kilometre. These cones varied in length from 6 to 24 cm., with all intermediate sizes. Also on each tree were cones of various lengths, but the longest were confined to two or three trees among the several hundred examined. Dimensions of leaves also varied with individual trees; not infrequently the leaves of a tree were twice the length of those of an adjacent tree. Such variations appear in many species and in many localities. Plate XII. Fig. 119, Two cones. Fig. 120, Leaf-fascicle. Fig. 121, Magnified leaf-section. Fig. 122, Conelets. Fig. 123, A cultivated tree in Massachusetts. [Illustration: PLATE XII. P. MONTICOLA (117, 118), STROBUS (119-123)] =Paracembra= Umbo of the cone-scale dorsal. Scales of the conelet mucronate or aristate. Epiderm and hypoderm of the leaf similar, appearing as a single tissue; resin-ducts external. Pits of the ray-cells small. The wood of this subsection differs from that of other species, except that of P. pinea, in the Picea-like characters of the medullary rays--tracheids with smooth walls combined with the thick walls and small pits of the ray-cells. On the character of the seeds the species may be divided into three groups. Seeds wingless IV. Cembroides. Seeds with a short, ineffective, articulate wing V. Gerardianae. Seeds with a long and effective wing VI. Balfourianae. =IV. CEMBROIDES= Seeds wingless, the nut large, wholly or partly bare of membranous cover. Cones varying from yellow-ochre to deep red-orange in color. These are the Nut Pines, growing on the arid slopes and table-lands above the great plateau of northern Mexico and its extension into the southwestern United States. There are three distinct species. Leaves entire, the sheath deciduous. Cones subglobose, subsessile 13. cembroides. Cones cylindrical, pedunculate 14. Pinceana. Leaves serrulate, the sheath persistent 15. Nelsonii. 13. PINUS CEMBROIDES