Fig. 166, Fruit of three seasons. Fig. 167, Cone-scales and seed. Fig. 168, Magnified leaf-section. Fig. 169, Habit of the tree. [Illustration: PLATE XVIII. PINUS PINEA] =Pinaster= Bases of the bracts subtending leaf-fascicles decurrent. Seeds with an effective articulate wing. Umbo of the cone-scales dorsal. Leaves serrulate, stomatiferous on all faces, the sheath persistent. Walls of the tracheids of the medullary rays dentate. Forty-two of the sixty-six species of Pinus are included in this subsection. As a group they are clearly circumscribed by several correlated characters and are more closely interrelated than the twenty-four species previously described. The distinctions of umbo and seed have disappeared. The umbo here is invariably dorsal, the seed-wing invariably articulate. New forms, however, are gradually evolved--the seed with a thick wing-blade, the indurated oblique cone, the serotinous cone with its intermittent seed-release, and the multinodal spring-shoot. There are, moreover, new forms of leaf-hypoderm and a new position of the resin-duct. Of these new characters, the thick wing-blade attains such proportions in the three species of the Macrocarpae that they can be grouped apart. But the characters that finally culminate in a lateral oblique serotinous cone are so gradually and irregularly developed that they offer no divisional distinctions. With the aid of wood and leaf characters, however, groups can be established which preserve the evolutionary sequence and, at the same time, the obvious affinity of the species. Wing-blade thin or slightly thickened at the base. Cones dehiscent at maturity. Pits of the ray-cells large X. Lariciones Pits of the ray-cells small XI. Australes Cones serotinous, pits of the ray-cells small XII. Insignes Wing-blade very thick XIII. Macrocarpae The species of this subsection are very difficult, if not impossible, to classify by the usual method, which groups all species under a few characters assumed to be invariable and of fundamental importance. Such a method can be successfully applied to the Soft Pines and to some of the Hard Pines, but cannot be applied to all the Hard Pines without forcing some of them into unnatural associations. To take an example, the group Pseudostrobus, characterized by pentamerous leaf-fascicles, appears in many systems. In this group are placed P. Torreyana and P. leiophylla. Another group, with trimerous fascicles, contains P. Sabiniana and P. taeda. Now there are no two species more obviously related by important peculiarities than P. Torreyana and P. Sabiniana; nevertheless they are, by this method, kept apart and associated with species which they resemble in no important particular.