PART II 



CLASSIFICATION OF THE SPECIES 



The following classification is based on the gradual evolution of the fruit from a cone symmetrical 

 in form, parenchymatous in tissue, indehiscent and deciduous at maturity, releasing its wingless seed 

 by disintegration — to a cone oblique in form, very strong and durable in tissue, persistent on the 

 tree, intermittently dehiscent, releasing its winged seeds partly at maturity, partly at indefinite inter- 

 vals during several years. This evolution embraces two extreme forms of fruit, one the most primi- 

 tive, the other the most elaborate, among Conifers. 



Two sections of the genus, Soft and Hard Pines, are distinguished by several correlated characters, 

 and moreover are distinct by obvious differences in the tissues of their cones as well as in the quality 

 and appearance of their wood. 



With the Soft Pines the species group naturally under two subsections on the position of the umbo, 

 the anatomy of the wood and the armature of the conelet. In one subsection (Cembra) are found 

 three species, P. cembra and its allies, with the cone-tissues so completely parenchymatous that the 

 cones cannot release the seeds except by disintegration. In both subsections there is a gradual evo- 

 lution from a wingless nut to one with an effective wing, adnate in one subsection, adnate and 

 articulate in the other. The different stages of this evolution are so distinct that the Soft Pines 

 are easily separated into definite groups. 



Among the Hard Pines a few species show characters that are peculiar to the Soft Pines. These 

 exceptional species form a subsection (Parapinaster) by themselves. 



With the remaining species, the majority of the Pines, the distinctions that obtain among Soft 

 Pines have disappeared. The dorsal umbo, the articulate seed-wing, the persistent fascicle-sheath, 

 the dorsal and ventral stomata of the leaf and its serrate margins, the dentate walls of the ray- 

 tracheids have become fixed and constant. But a new form of seed-wing appears, with a thickened 

 blade, assuming such proportions in P. Sabiniana and its two allies that these three constitute a 

 distinct group, remarkable also for the size of its cones. 



Here also appear a new form of fruit, the oblique cone, and a new method of dissemination, the 

 serotinous cone. Associated with the latter are the persistent cone and the multinodal spring-shoot. 

 These characters do not develop in such perfect sequence and regularity that they can be em- 

 ployed for grouping the species without forcing some of them into unnatural association. The 

 oblique cone first appears sporadically here and there and without obvious reason. The persistent 

 cone, the first stage of the serotinous cone, is equally sporadic in the earlier stages of evolution. The 

 same may be said of the multinodal shoot. 



Nevertheless these characters show an obvious progression toward a definite goal, where they are 

 all united in a small group of species remarkable for the form and texture of their cones, for a peculiar 

 seed-release and for the vigor and rapidity of their growth. It is possible, with the assistance of other 

 characters, to segregate these species in three groups in which the affinities are respected and the 

 general trend of their evolution is preserved. 



The first group, the Lariciones, contains species with large ray-pits, cones dehiscent at maturity, 

 and uninodal spring-shoots. They are, with two exceptions, P. resinosa and P. tropicalis, Old World 

 species. 



