50 GENUS PINUS 



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 dis- 

 tinctions. With the aid of wood and leaf characters, however, groups can be established which pre- 

 serve 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 impor- 

 tance. 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. 



An attempt is made here to avoid such incongruities. Groups X, XI and XII represent different 

 stages of evolution. In the Lariciones the cone is symmetrical, and dehiscent and deciduous at 

 maturity, while the spring-shoot is uninodal. In the Australes there is a similar cone, but the spring- 

 shoot gradually becomes multinodal. In the Insignes the cone is oblique, persistent and serotinous, 

 and the spring-shoot is multinodal. 



These definitions state the degree of evolution attained by each group, but not all the species of a 

 group conform exactly with its definition. In each group are species with a characteristic of another 

 group. Among the Lariciones are a few species with both symmetrical and oblique cones, and two 

 with persistent cones. Similar exceptions occur among the Australes. Among the Insignes are a few 

 species with symmetrical cones, and two with cones that are rarely, if ever, serotinous. 



There is, however, no difficulty in fixing the systematic position of these exceptional species 

 through other characters which show their true affinity. They are placed with the species which 

 they most resemble. Their exceptional characters are merely the evidence of the evolution that 

 pervades and unites the groups. Therefore the definition of a group is not necessarily the exact 

 definition of its species, and a species is placed in a group because all its characters, specific and 

 evolutional, show a closer affinity with that group than with the species of any other. 



