The Pines are confined to the northern hemisphere, but grow in all climates and under all conditions of soil, temperature and humidity where trees can grow. Some of the species are of very restricted range, but others are adaptable and can cover wide areas. The sixty-six species are distributed as follows-- Eastern Hemisphere, 23. 1 exclusively African (Canary Islands). 2 exclusively European. 3 about the Mediterranean Basin. 2 common to Europe and northern Asia. 14 exclusively Asiatic. Western Hemisphere, 43. 28 in western North America, of which 12 are confined to Mexico and Central America. 15 in eastern North America, of which 2 are exclusively West Indian. The two sections of the genus correspond with those of Koehne (Deutsch. Dendrol. 28 [1893]) and his two names, Haploxylon and Diploxylon, are adopted here, together with his two subsections of Haploxylon, Cembra and Paracembra. Of the two subsections of Diploxylon, Pinaster has been employed by Endlicher (Syn. Conif. 166 [1847]) and later authors for smaller or larger groups of Hard Pines. The subsection Parapinaster is now proposed. The names of groups, Cembrae, Strobi, Cembroides, Gerardianae, Balfourianae, Pineae, Lariciones and Australes, are taken from Engelmann's Revision of the Genus Pinus (Trans. Acad. Sci. St. Louis, iv. 175-178 [1880]). The remainder, Flexiles, Leiophyllae, Longifoliae, Insignes and Macrocarpae, are here proposed. In order to bring the illustrations within the limits of the page the dimensions of cone and leaf, as shown on the plates, are a little smaller than life. In plates X and XXV the reproductions of the cones are reduced to 2/5 life-size. SECTIONS, SUBSECTIONS, AND GROUPS Bases of the fascicle-bracts non-decurrent A--HAPLOXYLON Umbo of the cone-scale terminal a--Cembra Seeds wingless. Cones indehiscent I. Cembrae Cones dehiscent II. Flexiles Seed with an adnate wing III. Strobi Umbo of the cone-scale dorsal b--Paracembra Seeds wingless IV. Cembroides Seed-wing short, ineffective V. Gerardianae Seed-wing long, effective VI. Balfourianae Bases of the fascicle-bracts decurrent B--DIPLOXYLON Fascicle-sheath or seed of Haploxylon c--Parapinaster Fascicle-sheath deciduous VII. Leiophyllae Fascicle-sheath persistent. Seed-wing of the Strobi VIII. Longifoliae Seed-wing of the Gerardianae IX. Pineae Fascicle-sheath persistent, seed-wing articulate, effective d--Pinaster